By the Certified Technicians at THE Water Heater Company Noritz Authorized Service Providers | Three Locations Serving Ventura County, Los Angeles County, Orange County & Santa Barbara Since 2018 Last Updated: May 2026
As a proud owner of a Noritz tankless water heater, you can enjoy endless hot water on demand, energy savings, and a compact design that takes up less space than traditional tank water heaters. However, like any other appliance, your tankless water heater may experience occasional malfunctions or error codes that require troubleshooting and repair. Knowing what these error codes mean and how to fix them can help you avoid costly repairs and extend the life of your water heater. In this article, we’ll cover the most common Noritz tankless water heater error codes and their meanings.
Your Noritz Is Talking to You. Here’s How to Understand What It’s Saying.
You walked over to your Noritz tankless water heater and saw a code flashing on the display. Maybe you have no hot water. Maybe the unit is beeping. Either way, you want to know: What does this mean? Is it serious? And what do I do next?
You are in the right place.
This is the most complete guide to Noritz tankless water heater error codes available anywhere. We are THE Water Heater Company — a Noritz Authorized Service Provider with three locations across Southern California, serving Ventura County, Los Angeles County, Orange County, and the City of Santa Barbara. Our certified technicians work on Noritz units every single day from Camarillo to Van Nuys to Santa Ana. We wrote this guide using Noritz’s own official documentation, our factory training, and years of real-world field experience.
We will explain every error code in plain English — what it means, what is causing it, and what needs to happen next.
But before we get to the codes, there is something important you need to understand first.
⚠️ A Critical Safety Warning Before You Read Any Further
Noritz tankless water heaters are not simple appliances. They are sophisticated systems that sit at the intersection of four potentially dangerous forces inside your home:
- Natural Gas or Propane — A gas leak or improper gas pressure is not something you can safely troubleshoot without professional training and the right tools. Gas leaks can cause fires, explosions, and carbon monoxide poisoning.
- High-Voltage Electricity — Noritz units use electronic control boards, sensors, solenoids, and wiring that carry live electrical current. Working inside the unit without proper training can cause serious injury or death.
- Pressurized Water — The water moving through a tankless heater is under pressure. Incorrect handling of connections, valves, or components can cause water damage or scalding burns.
- Combustion Exhaust — Tankless water heaters produce exhaust gases, including carbon monoxide, that must be properly vented out of your home. A blocked or damaged vent is a life-safety emergency.
This combination of gas, electricity, water, and exhaust is why Noritz tankless water heaters should only be diagnosed and repaired by a licensed, trained professional. This is not a DIY appliance in the same way that changing a light switch might be. The consequences of a mistake are serious.
This guide is written to help you understand what is happening with your unit — not to guide you through a repair. Think of it the same way you would think of a medical reference guide: knowing what a diagnosis means is helpful and important, but it does not replace a trained doctor performing the actual procedure.
If you are in Ventura County, Los Angeles County, Orange County, or the Santa Barbara area and your Noritz unit is showing an error code, call THE Water Heater Company at (877) 274-1485. We are Noritz Authorized Service Providers with three locations across Southern California, and we are here to help.
How Do Noritz Error Codes Work?
When something goes wrong with your Noritz tankless water heater, the unit’s control system detects the problem and displays an error code on the remote controller or display panel. The code will appear where you normally see the water temperature setting — usually as “Er” followed by a number (for example, “Er:11”).
An audible beeping alarm usually accompanies the error code to get your attention.
These codes are actually a helpful feature. According to Randy Oshiro, Assistant Manager of Engineering at Noritz, “These codes can diagnose problems that otherwise might remain unnoticed until unit failure, thus saving on repair and replacement costs.” In other words, your Noritz is designed to tell you when something is wrong — before that something turns into a much bigger problem.
How to Check Your Error Code History
Your Noritz unit keeps a memory of past error codes even after they have been cleared. Here is how to access that history using your remote controller:
- Press the Power (On/Off) button to turn the remote off.
- Press the Up and Down arrow buttons at the same time until “03” appears on the display.
- Press the Down arrow to enter the error code history. Error codes are stored in maintenance monitors 91 through 98. The most recent code will be followed by “91.”
- Press the Up button to scroll through additional codes.
- Keep pressing Up until you see “000” on the display.
- Once you see “000,” press the Up and Down buttons together until the display goes blank.
- Press the Power button to turn the remote back on.
This history can be extremely helpful when your technician arrives — it tells the full story of what your unit has been experiencing, not just the most recent event.
The Most Important Thing to Understand: Soft Lockouts vs. Hard Lockouts
This is something most guides do not explain — and it is one of the most important things to understand about your Noritz unit.
Not all error codes are equal. Noritz officially classifies error conditions into two categories, and knowing the difference helps you understand how serious a situation is.
Here is the exact language directly from the official Noritz NRCP1112-DV Owner’s Manual:
“The water heater shall enter a soft lockout condition if the error is such that it can return to normal operation once the condition relieves itself (overheat conditions, temperature sensor open or shorts, etc.). The water heater shall enter a hard lockout if the condition indicates the unit detected a condition preventing safe operation.”
Let us break that down into plain English.
What Is a Soft Lockout?
A soft lockout means the unit detected a problem, but the problem may be temporary. In some cases, the unit may keep running. In other cases, you can unplug the unit, wait 30 seconds, plug it back in, and the unit may start working again — at least temporarily.
The critical thing to understand about soft lockouts: They do not go away on their own. The underlying problem is still there. If the same soft lockout error code happens repeatedly without being fixed, the unit will eventually lock itself out permanently.
Here is a real example: Error Code 90 is a soft lockout. It means there is a combustion abnormality — the unit is not burning gas the way it should. If your unit shows Error Code 90 three times without the problem being fixed, it will display Error Code 903 — and the unit will lock itself out completely and stop working.
The “3” at the end of 903 means the code 90 occurred three times. This escalation pattern is built into how Noritz units protect themselves from repeated unsafe conditions.
The takeaway: A soft lockout is a warning. Do not ignore it just because the unit seems to be working. Call a professional before it escalates into a full lockout.
What Is a Hard Lockout?
A hard lockout means the unit has detected a condition that Noritz has determined is unsafe for the unit to continue operating. The unit will shut itself down and will not restart until the problem has been diagnosed and fixed by a trained technician.
Hard lockout codes are Noritz’s built-in safety system. The unit is protecting you, your family, and your home by refusing to operate under dangerous conditions.
Examples of hard lockout conditions include ignition failure (Er.11), condensate line problems (Er.29), gas leakage detection (Er.40), and flame detection without ignition (Er.72).
The takeaway: A hard lockout means stop. Do not attempt to force the unit to restart by unplugging and replugging it repeatedly. Call a professional immediately.
The Complete Noritz Error Code Reference
Below is a comprehensive breakdown of every Noritz error code. Each entry includes:
- What the code means in plain language
- The official Noritz definition
- Common causes that our technicians see in the field
- Lockout type (soft or hard)
- What you should do
🔧 Error Code 05 — Service Reminder
What does Noritz Error Code 05 mean?
Error Code 05 is not actually an error — it is a scheduled maintenance reminder. Your unit is telling you it is time for a professional service visit.
Lockout Type: Not a lockout. Unit continues to operate.
What causes it: This code appears automatically after a set number of operating hours, similar to the oil change reminder light in your car.
What you should do: Do not reset or ignore this code without scheduling a service visit. Resetting it without performing maintenance can shorten the life of your unit. Call a Noritz Authorized Service Provider to perform a full inspection, descale, and combustion cleaning.
🔴 Error Code 10 — Combustion Abnormality After Shutdown
What does Noritz Error Code 10 mean?
Error Code 10 means the unit detected combustion activity — flame or burning — even after the unit was supposed to shut down. In other words, something kept burning when it should have stopped.
Lockout Type: Soft lockout.
Common causes:
- Foreign material on the burner that continued burning after the gas supply was cut
- Debris, grease, or buildup inside the combustion chamber
- A faulty gas valve that did not fully close
What you should do: Do not attempt to inspect the burner yourself. This code involves the gas combustion system and requires a licensed technician to safely inspect and clean the burner and verify the gas valve is functioning correctly.
🔴 Error Code 11 — Ignition Failure
What does Noritz Error Code 11 mean?
Error Code 11 means your unit tried to ignite and failed. There was no flame. The unit made an attempt to light the burner and nothing happened.
Three things are needed to ignite a tankless water heater: air, a spark, and gas. Error Code 11 means at least one of those three things was missing or not working.
Lockout Type: Hard lockout. Directly cited in Noritz’s official owner’s manual as a hard lockout condition.
Common causes:
- No gas supply, or the gas valve is not fully open
- Incorrect gas type (unit set for natural gas but connected to propane, or vice versa)
- Low gas pressure
- Debris or corrosion on the ignition rod or igniter plug
- Blocked air intake or exhaust vent
- A faulty igniter or gas valve
What you should do: This is a hard lockout — the unit will not restart on its own. A licensed technician will need to check gas pressure with a digital manometer, inspect the igniter and flame rod, verify the venting system, and confirm the correct gas type is being supplied.
🔴 Error Code 12 — Flame Loss During Operation
What does Noritz Error Code 12 mean?
Error Code 12 means the unit successfully ignited, but the flame went out while the unit was running. The burner lit, but could not stay lit.
Lockout Type: Hard lockout.
Common causes:
- Low or inconsistent gas pressure (especially common with propane when the tank is running low)
- Multiple gas appliances running at the same time competing for gas supply
- A blocked or improperly sized exhaust vent
- A dirty or corroded flame rod that cannot detect the flame
- A tripped earthquake shutoff valve on the gas line
What you should do: A technician will measure incoming gas pressure, inspect the venting system, and clean or replace the flame rod as needed. If you have propane, check that your tank is not running low.
🔴 Error Code 13 — CO Alarm Device Malfunction
What does Noritz Error Code 13 mean?
Error Code 13 indicates a problem with an optional carbon monoxide (CO) alarm device connected to the unit.
Lockout Type: Hard lockout.
Common causes:
- A fault or disconnection in the CO alarm wiring
- A malfunctioning CO detection device
- Improper installation of the CO alarm accessory
What you should do: Carbon monoxide is odorless, colorless, and deadly. Any issue with CO detection equipment should be treated as a serious safety matter. Do not attempt to reset or bypass this code. Call a licensed technician immediately.
🔴 Error Code 14 — Thermal Fuse Failure / Heat Exchanger Overheat
What does Noritz Error Code 14 mean?
Error Code 14 means the thermal fuse has blown. The thermal fuse is a safety device wrapped around the heat exchanger. When the outside surface of the heat exchanger gets dangerously hot, the fuse breaks to shut the unit down and prevent further damage — or worse.
Lockout Type: Hard lockout.
Common causes:
- Scale and mineral buildup inside the heat exchanger (extremely common in areas with hard water, including much of Southern California)
- Scale acts as an insulator, trapping heat inside the heat exchanger instead of transferring it to the water
- Over time, the surface temperature of the heat exchanger rises until the thermal fuse trips
- Blocked venting can also cause overheating
What you should do: The thermal fuse itself will need to be replaced. However, replacing just the fuse without addressing the underlying cause — usually scale buildup — means the same code will come back. A full descale and heat exchanger inspection is typically required. In severe cases, the heat exchanger itself may need to be replaced.
This is one of the most common codes we see in Ventura County. Southern California has notoriously hard water, and scale buildup is the number one reason Noritz units are taken out of service prematurely. Annual descaling maintenance is the single best investment you can make in your tankless water heater.
🟡 Error Code 16 — Outlet Water Temperature Too High
What does Noritz Error Code 16 mean?
Error Code 16 means the water leaving your unit spiked to an abnormally high temperature. The unit detected dangerously hot water at the outlet and shut down to protect you and the system.
Lockout Type: Soft lockout.
Common causes:
- Scale buildup in the heat exchanger reducing heat transfer efficiency (same root cause as Code 14)
- Incorrect gas type being supplied to the unit
- Improperly adjusted gas manifold pressure
- Very low water flow rate through the unit
What you should do: Do not dismiss this code. Scalding hot water is a real safety risk, especially in homes with children or elderly residents. A technician will descale the unit, verify the gas type and pressure, and ensure the water flow rate is adequate.
🔴 Error Code 20 — High Limit Switch Triggered
What does Noritz Error Code 20 mean?
Error Code 20 means the high limit switch was triggered. This switch is a safety device — it monitors water temperature inside the unit, and if the water temperature rises above a safe threshold (between 176°F and 205°F), the switch cuts power to the unit to prevent damage or injury.
Lockout Type: Hard lockout requiring a power reset (unplug the unit, allow it to cool, then restore power). However, if the underlying cause is not fixed, the code will return.
Common causes:
- Scale buildup in the heat exchanger (again — this is a pattern in hard water areas)
- Blocked venting restricting airflow
- A loose or faulty wiring connection at the high limit switch
What you should do: While you can attempt a power reset (unplug for 60 seconds, then plug back in), the code will return if the root cause is not addressed. A technician needs to inspect the heat exchanger, perform a descale if needed, and verify the venting and wiring.
🔴 Error Code 29 — Condensate Drainage Problem
What does Noritz Error Code 29 mean?
Error Code 29 applies only to condensing tankless water heaters — the high-efficiency models that recover extra heat from exhaust gases. As part of that process, the unit produces condensate (water), which must drain out through a dedicated drain line. Error Code 29 means that drainage is not happening correctly.
Lockout Type: Hard lockout. Directly cited in Noritz’s official owner’s manual as a hard lockout condition.
Common causes:
- A blocked or clogged condensate drain line
- A drain line that is too small (must be at least ½ inch inner diameter)
- A drain line that is not sloped correctly toward the drain point
- A frozen condensate drain line (in cold weather conditions)
What you should do: Call a licensed technician. If the condensate cannot drain, it can back up into the unit and cause damage or flooding. Do not attempt to clear drain lines connected to the gas combustion system yourself.
🟡 Error Code 30 — Air Thermistor Abnormality
What does Noritz Error Code 30 mean?
Error Code 30 means there is a problem with the air thermistor — a sensor that measures the temperature of the incoming air. The sensor is either disconnected, shorted, or faulty.
Lockout Type: Soft lockout.
Common causes:
- Loose or disconnected wiring at the thermistor
- A failed thermistor sensor
- Damage to the sensor from moisture or debris
What you should do: A technician will check the wiring connections and test the thermistor. If it has failed, it will need to be replaced.
🟡 Error Code 31 — Inlet (Cold Water) Thermistor Failure
What does Noritz Error Code 31 mean?
Error Code 31 means the inlet thermistor — the sensor that measures the temperature of the cold water coming into the unit — is not working properly.
Lockout Type: Soft lockout.
Common causes:
- A damaged or failed thermistor
- Loose or corroded wiring connections at the sensor
What you should do: The thermistor will need to be tested and replaced by a licensed technician. This sensor is important because it helps the unit calculate how much energy is needed to heat the water to your desired temperature.
🟡 Error Code 32 — Outlet (Hot Water) Thermistor Failure
What does Noritz Error Code 32 mean?
Error Code 32 means the outlet thermistor — the sensor that measures the temperature of the hot water leaving the unit — is not working correctly.
Lockout Type: Soft lockout.
Common causes:
- A damaged or failed thermistor
- Loose or corroded wiring connections
What you should do: A licensed technician will test and replace the thermistor as needed. Without an accurate outlet temperature reading, the unit cannot properly regulate water temperature.
🟡 Error Code 33 — Heat Exchanger Thermistor Failure
What does Noritz Error Code 33 mean?
Error Code 33 means the thermistor attached to the heat exchanger itself is malfunctioning. This sensor monitors the temperature of the heat exchanger to prevent overheating.
Lockout Type: Soft lockout.
Common causes:
- A failed thermistor sensor
- Loose or disconnected wiring
What you should do: A technician will test and replace the sensor. Because this sensor is part of the unit’s safety monitoring system, it should not be ignored.
🟡 Error Code 35 — Exhaust Thermistor Abnormality
What does Noritz Error Code 35 mean?
Error Code 35 means the sensor monitoring the temperature of the exhaust gases is not reading correctly.
Lockout Type: Soft lockout.
Common causes:
- A faulty or disconnected exhaust thermistor
- Wiring damage near the exhaust area
What you should do: A technician will verify connections and replace the sensor if needed. Exhaust temperature monitoring is an important safety function — do not ignore this code.
🔴 Error Code 40 — Gas Leakage Detected
What does Noritz Error Code 40 mean?
Error Code 40 means the unit has detected a gas leak. This is a serious safety emergency.
Lockout Type: Hard lockout. Directly cited in Noritz’s official owner’s manual as a hard lockout condition.
What you should do immediately:
- Do not try to find the leak yourself.
- Do not operate any electrical switches.
- Leave the area immediately.
- Call your gas utility’s emergency line from outside the home.
- Do not re-enter until the gas company has cleared the home.
Once the gas leak has been addressed by the gas utility, call a Noritz Authorized Service Provider to inspect the unit before it is put back into service.
🔴 Error Code 45 — Internal Water Leak Detected
What does Noritz Error Code 45 mean?
Error Code 45 means moisture or water has been detected inside the unit. This code is specific to Noritz NRCP and CB model units.
Lockout Type: Hard lockout.
Common causes:
- A water leak from internal connections, fittings, or heat exchanger
- Condensation buildup due to temperature differences
- A faulty leak sensor
What you should do: A technician will remove the front cover, locate the leak sensor, and identify the source of moisture. If there is an active internal water leak, it must be repaired before the unit can be safely operated.
🔴 Error Code 51 — Gas Manifold Solenoid Failure
What does Noritz Error Code 51 mean?
Error Code 51 means there is a fault with the gas manifold solenoid valve — the component that controls how gas is delivered to the burner.
Lockout Type: Hard lockout.
Common causes:
- A failed gas manifold solenoid valve
- Damaged or loose wiring at the solenoid connections
- In some cases, water dripping onto the manifold from a leak above it
What you should do: This is an internal gas component repair. A licensed technician will test the solenoid connections and, if needed, replace the gas manifold. If water is found on the manifold, the source of that leak must also be identified and repaired.
🔴 Error Code 52 — Exhaust Blockage
What does Noritz Error Code 52 mean?
Error Code 52 means the unit has detected a blockage in the exhaust venting system.
Lockout Type: Hard lockout.
Common causes:
- A bird nest, debris, or foreign object in the exhaust vent pipe
- Ice or frost blocking the vent in cold weather
- A vent pipe that is too long or has too many bends, restricting airflow
- A damaged or collapsed vent pipe
What you should do: Never operate a unit with a blocked exhaust. Carbon monoxide and other combustion gases must be able to safely exit your home. A technician will inspect and clear the venting system and verify it meets Noritz’s installation specifications.
🟡 Error Code 57 — Incoming Water Pressure Too Low
What does Noritz Error Code 57 mean?
Error Code 57 means the water pressure coming into the unit is too low for proper operation.
Lockout Type: Soft lockout.
Common causes:
- Low water pressure in the home’s supply line
- A partially closed water supply valve to the unit
- A clogged inlet filter screen on the unit
- A failing water pressure regulator on the home’s main line
What you should do: A technician will check the inlet water pressure, inspect the inlet filter, and verify the water supply valve is fully open. If your home has consistently low water pressure, a pressure regulator evaluation may also be recommended.
🟡 Error Code 59 — Combustion Abnormality / Low BTU Input
What does Noritz Error Code 59 mean?
Error Code 59 means the unit is not getting enough energy from combustion. It is burning, but not at the level needed to properly heat the water.
Lockout Type: Soft lockout.
Common causes:
- Insufficient fresh air supply to the combustion chamber
- Blockages in the exhaust or intake venting
- A dirty fan motor or burner chamber
- The unit’s elevation settings (DIP switches) not properly configured for your altitude
What you should do: A technician will clean the fan motor and burner, clear any venting obstructions, and verify the unit is configured correctly for your installation location.
🔴 Error Code 61 — Fan Motor Failure
What does Noritz Error Code 61 mean?
Error Code 61 means the fan motor inside the unit has failed or is not operating correctly. The fan is critical — it controls airflow through the combustion chamber, which is essential for safe and efficient burning.
Lockout Type: Hard lockout.
Common causes:
- A failed fan motor
- A fan motor not receiving proper voltage
- A fan bearing that has worn out
- A blockage preventing the fan from spinning
What you should do: A technician will test the incoming voltage to the fan motor, check for physical blockages, and replace the fan motor if it has failed. A unit should never be operated without a functioning fan — without proper airflow, combustion gases including carbon monoxide cannot be safely managed.
🟡 Error Code 63 — Recirculation Abnormality (Condensing Models)
What does Noritz Error Code 63 mean?
Error Code 63 indicates a problem with the recirculation system on condensing Noritz models (NRCR series). It can also appear on models with built-in recirculation pumps.
Lockout Type: Soft lockout.
Common causes:
- A clogged return line filter
- A problem with the crossover valve or its filter
- In some cases, a failed PC control board
What you should do: A technician will check the return line filter, inspect the crossover valve, and evaluate the control board.
🔴 Error Code 65 — Main Water Servo Abnormality
What does Noritz Error Code 65 mean?
Error Code 65 means the main water servo valve is not functioning properly. This valve controls water flow through the unit.
Lockout Type: Hard lockout.
Common causes:
- A blocked or stuck water servo valve
- A failed servo motor
- Loose or damaged wiring at the servo connections
What you should do: A licensed technician will inspect and test the servo valve and replace it if needed.
🔴 Error Code 66 — Bypass Flow Control Valve Failure
What does Noritz Error Code 66 mean?
Error Code 66 means the bypass flow control valve — which helps regulate water temperature by blending hot and cold water — is not working correctly.
Lockout Type: Hard lockout.
Common causes:
- A blocked bypass servo valve
- A failed bypass flow control valve
- Wiring issues at the valve connections
What you should do: A technician will inspect the bypass servo for restrictions and replace the valve if it has failed.
🔴 Error Code 67 — Air Gas Mixer (AGM) Abnormality
What does Noritz Error Code 67 mean?
Error Code 67 means there is a problem with the Air Gas Mixer, or AGM. The AGM is an important component that precisely balances the mixture of air and gas going into the burner. If that balance is off, combustion is inefficient and potentially unsafe.
Lockout Type: Hard lockout.
Common causes:
- Excessive debris or buildup inside the AGM housing, causing the dial to stick
- Loose or damaged wiring at the AGM
- A failed AGM unit
What you should do: A technician will remove and inspect the AGM, clean the housing, reset the air-gas calibration, and verify the wiring. This is an internal gas system component — it should only be handled by a trained professional.
🔴 Error Code 70 — Circuit Board Failure
What does Noritz Error Code 70 mean?
Error Code 70 means there is a fault with the unit’s main circuit board — the electronic brain that controls all of the unit’s operations.
Lockout Type: Hard lockout.
Common causes:
- A failed circuit board
- Power surge damage
- Moisture intrusion into the control board
What you should do: A technician will diagnose the board and replace it if necessary. Circuit board replacement on a gas appliance involves working with both electrical and gas components and should only be performed by a licensed professional.
🔴 Error Code 71 — Gas Valve Drive Circuit Abnormality
What does Noritz Error Code 71 mean?
Error Code 71 means there is a problem with the circuit that drives the gas valve — the electrical system that tells the gas valve when to open and close. Without proper gas valve operation, the unit cannot safely control gas flow.
Lockout Type: Hard lockout.
Common causes:
- A failed circuit board
- Voltage fluctuations from a battery backup, generator, or solar power system
- A faulty gas valve itself
What you should do: A technician will test the voltage output from the circuit board and inspect the gas valve. This code is particularly common on units connected to alternative power sources with inconsistent voltage output.
🔴 Error Code 72 — Flame Detected Without Ignition Sequence
What does Noritz Error Code 72 mean?
Error Code 72 means the unit’s flame sensor detected a flame when there should not have been one. In other words, the unit sensed fire without having started the ignition sequence. This is a serious safety condition.
Lockout Type: Hard lockout. Directly cited in Noritz’s official owner’s manual as a hard lockout condition.
Common causes:
- A faulty flame detection circuit
- A problem with the circuit board
- Improper grounding of the unit
- A failed flame rod
What you should do: This code indicates the unit’s safety systems are detecting a condition that should not exist. Do not attempt to reset or restart the unit. Call a licensed technician immediately.
🟡 Error Code 73 — Circuit Board Setting Error
What does Noritz Error Code 73 mean?
Error Code 73 means there is an error in the circuit board’s settings — specifically, the jumper connections or DIP switches that configure the unit for your specific installation.
Lockout Type: Soft lockout.
Common causes:
- A jumper wire or DIP switch was changed while the unit was powered on (this should never be done)
- The circuit board was programmed incorrectly during installation
- A power issue caused the board to lose its settings
What you should do: Try unplugging the unit for 30 seconds and plugging it back in. If the code clears and does not return, the unit may have self-corrected. If the code returns, a technician will need to verify the circuit board programming and DIP switch settings match your installation requirements.
🟡 Error Code F76 — Multi-Unit Communication Error
What does Noritz Error Code F76 mean?
Error Code F76 means two Noritz tankless water heaters connected together using a Quick Connect Cord are having a communication problem. This code applies only to homes or buildings with a multi-unit setup.
Lockout Type: Soft lockout.
Common causes:
- More than one remote controller is connected to the two-unit system (only one remote should be used when two units are connected)
- A damaged or disconnected Quick Connect Cord
- A wiring issue in the multi-unit setup
What you should do: Verify that only one remote controller is connected to the system. If the code persists after disconnecting the power and reconnecting, call a licensed technician to inspect the wiring and connection cord.
🟡 Error Code 90 — Combustion Abnormality (Soft Lockout — Escalates to 903)
What does Noritz Error Code 90 mean?
Error Code 90 is one of the most common Noritz error codes. It means the unit detected a combustion abnormality — the mixture of air and fuel inside the burner is not right. The unit is not burning gas the way it should.
Lockout Type: Soft lockout — but with a critical escalation warning.
Important: Error Code 90 is a soft lockout, which means the unit may continue to operate or can be temporarily reset by unplugging and replugging. However, if Error Code 90 occurs three times without the underlying problem being fixed, your unit will display Error Code 903 and lock itself out completely. The “3” in 903 indicates the code occurred three times. At that point, the unit will not restart until a licensed technician has diagnosed and resolved the issue.
Common causes:
- Insufficient gas supply or low gas pressure
- A blocked air intake or exhaust vent
- A dirty or restricted fan motor
- DIP switch settings that are not configured correctly for your elevation, pipe size, or vent length
- Scale buildup affecting combustion efficiency
What you should do: Do not keep resetting this code and hoping it goes away. Every reset without a fix brings you one step closer to a full lockout. Call a Noritz Authorized Service Provider. A technician will measure gas pressure, inspect the venting, clean the fan motor and combustion chamber, and verify all settings.
🟡 Error Code 91 — Incorrect Gas Type
What does Noritz Error Code 91 mean?
Error Code 91 means the unit is detecting that it may not be receiving the correct type of gas, or that the gas manifold pressure is set incorrectly.
Lockout Type: Soft lockout.
Common causes:
- The unit is configured for natural gas but connected to propane, or vice versa
- The gas manifold pressure was set incorrectly during installation
- A change in the gas supply characteristics
What you should do: A technician will check the rating plate on your unit to confirm what gas type it is configured for, verify the gas supply, and adjust manifold pressure to match manufacturer specifications.
🟡 Error Code 92 — Neutralizer Life Cycle Warning (First Notice)
What does Noritz Error Code 92 mean?
Error Code 92 is a maintenance warning specific to condensing Noritz models. It means the neutralizer — a component that treats the acidic condensate water produced by high-efficiency units — is approaching the end of its useful life.
Lockout Type: Soft lockout / maintenance warning.
Common causes: Normal wear. The neutralizer has a finite lifespan based on operating hours.
What you should do: Schedule a service visit soon. The neutralizer needs to be replaced before it reaches the end of its life (indicated by Error Code 93). After replacement, the burner timer must be reset by a technician.
🟡 Error Code 93 — Neutralizer End of Life (Final Warning)
What does Noritz Error Code 93 mean?
Error Code 93 means the neutralizer has reached the end of its life cycle. It needs to be replaced now.
Lockout Type: Soft lockout / urgent maintenance warning.
What you should do: Call a licensed technician immediately to replace the neutralizer and reset the system. Operating a condensing unit without a functional neutralizer can cause acidic condensate to drain improperly and damage your plumbing.
🔴 Error Code 94 / 941 / 942 — Exhaust Temperature Too High
What does Noritz Error Code 94 mean?
Error Code 94 (and its variants 941 and 942 on display window units) means the exhaust gases leaving the unit are too hot. Safe combustion produces exhaust at expected temperatures — when that temperature is excessively high, something is wrong with how the unit is burning or venting.
Lockout Type: Hard lockout.
Common causes:
- A blocked or restricted exhaust vent
- A combustion problem causing the unit to run at abnormally high temperatures
- Scale buildup in the heat exchanger affecting combustion efficiency
What you should do: Do not operate the unit. High exhaust temperatures can damage venting materials and create a fire hazard. Call a licensed technician to inspect the vent system and combustion components.
🟡 Error Code 99 — Combustion Abnormality (Similar to Code 90)
What does Noritz Error Code 99 mean?
Error Code 99 is similar to Error Code 90 — it indicates a gas combustion problem. The flame color should be blue (yellow tips are acceptable in small amounts, but a predominantly yellow flame indicates a problem).
Lockout Type: Soft lockout.
Common causes: Similar to Code 90 — gas supply issues, venting blockages, or combustion system problems.
What you should do: Same as Code 90. Call a Noritz Authorized Service Provider for diagnosis. Do not continue to reset without addressing the root cause.
🔴 Error Code 108 — Flow Sensor Failure
What does Noritz Error Code 108 mean?
Error Code 108 means the flow sensor — which detects when water is running through the unit and triggers the heating process — has failed or is not reading correctly.
Lockout Type: Hard lockout.
Common causes:
- A failed flow sensor
- Debris blocking the flow sensor
- Damaged wiring at the sensor
What you should do: A technician will inspect, clean, and test the flow sensor, and replace it if necessary. Without an accurate flow sensor reading, the unit cannot determine when to start heating water.
🔴 Error Code 903 — Combustion Lockout (Code 90 Occurred Three Times)
What does Noritz Error Code 903 mean?
Error Code 903 means that Error Code 90 — the combustion abnormality — occurred three times without being resolved. The unit has now locked itself out completely to prevent continued unsafe operation.
The “3” at the end of the code tells the story: this is a Code 90 that was ignored (or temporarily reset) two times too many.
Lockout Type: Hard lockout.
What you should do: The unit will not restart on its own. A licensed Noritz technician must diagnose the root combustion issue, make the necessary repairs, and clear the lockout. This code is the unit’s way of saying: “I tried to warn you three times. Now I need professional help before I run again.”
In our experience, Error Code 90 leading to a 903 lockout is almost always preventable with timely maintenance. If your unit shows Code 90, call us before it escalates.
🔴 Error Code 760 — Remote Controller Communication Error
What does Noritz Error Code 760 mean?
Error Code 760 means there is a communication problem between the unit and the remote controller.
Lockout Type: Soft lockout.
Common causes:
- A disconnected or damaged communication wire between the unit and remote
- More than one remote controller connected to a single unit
- A faulty remote controller
What you should do: Try unplugging the unit, waiting 30 seconds, and replugging. If the code returns, check that only one remote is connected and that the wiring is intact. If the problem persists, a technician will inspect the wiring and the remote controller.
🟡 Error Code C1 — Scale Buildup Warning (Premix Models)
What does Noritz Error Code C1 mean?
Error Code C1 appears on Noritz premix model units and indicates that the heat exchanger has significant scale buildup that is affecting performance.
Lockout Type: Soft lockout / maintenance warning.
Common causes: Hard water mineral deposits accumulating inside the heat exchanger over time. This is extremely common in Southern California.
What you should do: Schedule a professional descale service immediately. Left unaddressed, scale buildup leads to more serious failures including thermal fuse failure (Code 14), high limit switch trips (Code 20), and ultimately heat exchanger failure.
Quick Reference: All Noritz Error Codes at a Glance
| Code |
Description |
Lockout Type |
| 05 |
Service reminder |
No lockout |
| 10 |
Combustion after shutdown |
Soft |
| 11 |
Ignition failure |
Hard |
| 12 |
Flame loss during operation |
Hard |
| 13 |
CO alarm device malfunction |
Hard |
| 14 |
Thermal fuse failure |
Hard |
| 16 |
Outlet water temp too high |
Soft |
| 20 |
High limit switch triggered |
Hard (requires reset) |
| 29 |
Condensate drainage problem |
Hard |
| 30 |
Air thermistor abnormality |
Soft |
| 31 |
Inlet thermistor failure |
Soft |
| 32 |
Outlet thermistor failure |
Soft |
| 33 |
Heat exchanger thermistor failure |
Soft |
| 35 |
Exhaust thermistor abnormality |
Soft |
| 40 |
Gas leakage detected |
Hard — Emergency |
| 45 |
Internal water leak (NRCP/CB models) |
Hard |
| 51 |
Gas manifold solenoid failure |
Hard |
| 52 |
Exhaust blockage |
Hard |
| 57 |
Incoming water pressure too low |
Soft |
| 59 |
Combustion abnormality / low BTU |
Soft |
| 61 |
Fan motor failure |
Hard |
| 63 |
Recirculation abnormality |
Soft |
| 65 |
Main water servo abnormality |
Hard |
| 66 |
Bypass flow control valve failure |
Hard |
| 67 |
Air Gas Mixer (AGM) abnormality |
Hard |
| 70 |
Circuit board failure |
Hard |
| 71 |
Gas valve drive circuit abnormality |
Hard |
| 72 |
Flame detected without ignition |
Hard |
| 73 |
Circuit board setting error |
Soft |
| F76 |
Multi-unit communication error |
Soft |
| 90 |
Combustion abnormality |
Soft → becomes 903 after 3x |
| 91 |
Incorrect gas type |
Soft |
| 92 |
Neutralizer life warning (first notice) |
Soft |
| 93 |
Neutralizer end of life |
Soft |
| 94 / 941 / 942 |
Exhaust temperature too high |
Hard |
| 99 |
Combustion abnormality |
Soft |
| 108 |
Flow sensor failure |
Hard |
| 760 |
Remote controller error |
Soft |
| 903 |
Code 90 occurred 3 times — full lockout |
Hard |
| C1 |
Scale buildup (premix models) |
Soft |
What Is the Difference Between a Soft Lockout and a Hard Lockout? (FAQ)
Q: Can I reset a soft lockout myself? You can unplug the unit, wait 30 seconds, and plug it back in to clear a soft lockout temporarily. However, this does not fix the underlying problem. The code will return — and if it returns three times on certain codes like Error Code 90, it will escalate into a full hard lockout. Always have a soft lockout professionally diagnosed, even if the unit seems to be working after a reset.
Q: Can I reset a hard lockout myself? Some hard lockouts allow a power reset (pressing the power button off and on, or unplugging and replugging the unit). However, the unit locked itself out for a reason. Forcing a restart without fixing the underlying problem is unsafe and can cause further damage. Hard lockouts should always be diagnosed and cleared by a licensed technician.
Q: My unit keeps resetting and the code keeps coming back. What does that mean? It means the underlying problem has not been fixed. Repeatedly resetting an error code without professional diagnosis is not a solution — it is a countdown to a larger failure or a safety event. Call a professional.
Q: How do I know if my Noritz error code is serious? Any error code related to gas, flame, ignition, exhaust, or CO detection should be treated as serious immediately. Temperature and sensor codes are less immediately dangerous but still require professional attention. When in doubt, call a licensed technician.
Q: Is it safe to use my Noritz while it is showing an error code? It depends on the code. Some soft lockout codes may allow the unit to keep running temporarily. However, continuing to use a unit that is showing any error code — without understanding what the code means — is not recommended. The safest approach is always to call a professional for diagnosis.
Why Annual Maintenance Prevents Most of These Error Codes
Looking at the list above, you will notice a pattern. A significant number of the most common Noritz error codes — including 14, 16, 20, 59, 90, 903, and C1 — are directly related to two preventable issues:
- Scale buildup from hard water minerals accumulating inside the heat exchanger.
- 2. Combustion problems related to dirty components, restricted airflow, or clogged venting.
Both of these issues develop slowly over time, and both are almost entirely preventable with annual professional maintenance.
A standard Noritz maintenance service performed by a Noritz Authorized Service Provider includes:
- A full descale flush to remove mineral deposits from the heat exchanger
- A combustion cleaning to clear the fan motor, burner, and combustion chamber
- An inspection of all venting for blockages or damage
- A check of gas pressure and manifold settings
- An inspection of all sensors, wiring, and safety components
- A review of the error code history for any patterns or developing issues
Think of it like an oil change for your water heater. You would not skip oil changes and wait for your engine to seize. The same logic applies here.
Annual maintenance typically costs a fraction of what a major repair or early unit replacement would cost. In Southern California — where hard water is a year-round reality — it is especially important.
How Much Does a Noritz Error Code Repair Cost?
Every repair is different, and the cost depends on which code is present, what is causing it, and what parts (if any) need to be replaced. What we can tell you is this:
- A diagnostic visit will identify exactly what is wrong and give you a clear picture before any work begins.
- Simple fixes like descaling, sensor replacements, or DIP switch corrections are generally less expensive than part replacements.
- Catching a problem early — when it is still a soft lockout — is almost always less expensive than waiting until it escalates into a hard lockout or unit failure.
- Investing in annual maintenance is almost always less expensive than emergency repair calls.
We believe in transparent, honest pricing — no surprises, no pressure. Call us and we will give you a clear explanation of what is happening and what it will cost to fix it.
Call THE Water Heater Company — Your Noritz Authorized Service Provider
If your Noritz tankless water heater is showing an error code, THE Water Heater Company is here to help.
We are a Noritz Authorized Service Provider with three locations across Southern California — Camarillo, Van Nuys, and Santa Ana — serving homeowners throughout Ventura County, Los Angeles County, Orange County, and the City of Santa Barbara. Our certified technicians work on Noritz units every day. We know these systems inside and out.
We are Your Trusted Water Heater Authority — and we are ready to get your hot water back.
Sources: Noritz NRCP1112-DV Owner’s Manual (ManualsLib); Noritz CB199-DV Owner’s Manual (ManualsLib); Noritz America Knowledge Base (help.noritz.com); Noritz Blog — “Common Noritz Tankless Error Codes: Updated” (noritz.com, June 2022); Noritz Blog — “How to Resolve the Seven Most Common Noritz Tankless Error Codes” (noritz.com, November 2015). Field experience provided by THE Water Heater Company, Noritz Authorized Service Providers — Camarillo, Van Nuys, and Santa Ana, CA.