Rheem Tankless Water Heater Error Codes: The Complete Guide

By the Certified Technicians at THE Water Heater Company
Licensed Water Heater Specialists | Three Locations Serving Ventura County, Los Angeles County, Orange County & Santa Barbara Since 2018
Last Updated: July 2026

Your Rheem Is Talking to You. Here's How to Understand What It's Saying.

You walked past your Rheem tankless water heater and spotted a code on the display. Maybe the shower went cold first and you went looking. 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 Rheem tankless water heater error codes available anywhere — verified against Rheem's own official troubleshooting documentation, not copied from other websites. We are THE Water Heater Company — licensed water heater specialists with three locations across Southern California, serving Ventura County, Los Angeles County, Orange County, and the City of Santa Barbara. Our technicians work on Rheem units regularly from Camarillo to Van Nuys to Santa Ana.

One note that will save some readers a step: if your unit says Ruud, this guide is for you too. Ruud is Rheem's sister brand, and Ruud tankless water heaters are the same units with a different badge — the error codes match.

Before we get to the codes, there is something important you need to understand first.

⚠️ A Critical Safety Warning Before You Read Any Further

Rheem tankless water heaters are not simple appliances. They are sophisticated systems that sit at the intersection of four potentially dangerous forces inside your home:

1. 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.

2. High-Voltage Electricity — Rheem units use a control board, sensors, solenoid valves, and wiring that carry live electrical current. Rheem's own diagnostic procedures involve live voltage and resistance testing. Working inside the unit without proper training can cause serious injury or death.

3. 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.

4. 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 Rheem 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 Rheem or Ruud unit is showing an error code, call THE Water Heater Company at (877) 798-7487. Our phones are answered by a live person 24/7/365, and we are here to help.

How Do Rheem Error Codes Work?

When your Rheem tankless water heater detects a problem, it displays a code — usually a two-digit number — on the digital display on the front of the unit or on the remote controller. Newer Rheem models connected to the EcoNet app can also push alerts to your phone (those app-era codes use a different format; if yours does not match this guide, call us and we will decode it for your exact model).

These codes are a helpful feature — your Rheem is designed to tell you when something is wrong before that something turns into a much bigger and more expensive problem. And as you will see, a couple of Rheem's codes are not "broken" codes at all — they are the unit telling you something about how it is being used.

The Most Important Thing to Understand: Warnings vs. Lockouts

This is something most guides do not explain — and it is one of the most important things to understand about your Rheem unit.

Not all error codes are equal.

Note: Rheem does not use the terms "soft lockout" and "hard lockout" in their publicly available documentation. The following classification is based on THE Water Heater Company's field experience, applied to how each code actually behaves.

What Is a Soft Lockout (Warning)?

A soft lockout means the unit detected a condition that may be temporary or that is progressing — and it is telling you while there is still time to act cheaply.

Rheem's clearest example is the neutralizer pair on condensing models: Code 92 and Code 93. Code 92 appears during operation — the condensate neutralizer is nearing the end of its life. Code 93 appears when the neutralizer's life is over and it must be replaced. That is a two-stage countdown with a built-in shopping window: 92 is the unit saying "schedule me," 93 is the unit saying "you didn't."

The takeaway: A warning code is a gift. The repair is almost always cheaper on the warning than on the lockout that follows it.

What Is a Hard Lockout?

A hard lockout means the unit detected a condition where continuing to run would not be safe — failed ignition, flame loss, overheating, a gas valve fault. The unit shuts down and stays down until the underlying problem is found and fixed. Resetting may clear the display for a moment, but the code returns because the fault is still there.

Hard lockouts are your Rheem protecting your home. Do not fight the safety system. Call a professional.

Quick Reference: Rheem Error Codes at a Glance

Code	What It Means	Lockout Type
00	Continuous combustion for over 1 hour (usage condition, often recirculation-related)	Soft (usage warning)
11	No ignition	Hard
12	Flame failure (flame lost during operation)	Hard
13	Improper combustion (indoor units)	Hard
14	Overheat wrap / thermal safety fault	Hard
16	Over-temperature warning	Hard
24	Operational switch malfunction	Control fault
29	Condensate / neutralizer drainage issue (condensing models)	Hard
61	Fan motor fault	Hard
65	Water flow control valve fault	Hard
66	Water bypass valve fault	Hard
71	Gas inlet solenoid valve control fault	Hard
72	Flame sensing device fault	Hard
76	Remote controller communication failure	Communication fault
79	Fan motor current fault	Hard
80 / 81	Gas cut-off failure	Hard — same-day service
92	Neutralizer nearing end of life (condensing models)	Soft (warning)
93	Neutralizer life ended — replacement required	Hard
99	Blocked ventilation / imperfect combustion	Hard
P1	Water flow below minimum (under 0.66 GPM for 5+ seconds)	Operational
No code	Unit unresponsive / no display	—

Rheem has produced many tankless generations, and some models use additional codes not listed here — including app-format alerts on newer EcoNet-connected units. If your unit shows a code you don't see above, call us at (877) 798-7487 and we will tell you exactly what it means for your model.

The Codes, One by One

What Does Rheem Error Code 00 Mean?

Rheem Code 00 means the unit has been in continuous combustion for more than one hour. This is the most misunderstood code in Rheem's lineup — the unit is not broken. It is telling you it has been firing nonstop, and it is not designed to run continuously.

Lockout type: Soft — a usage warning. Per Rheem's guidance, closing all hot water taps resets it.
Common causes: a circulation pump running the unit around the clock (standard Rheem tankless units are not designed for continuous operation with circulation systems), a fixture left running, or — the sneaky one — a plumbing crossover or a leaking fixture that keeps a phantom demand on the unit. Dirty filters, fans, and heat exchanger fins make everything worse by forcing longer burns.
What you should do: if this code appears and you cannot explain it (nobody was running water for an hour), something in your plumbing is quietly demanding hot water. That deserves a professional look — and if you have a recirculation system on a unit not designed for it, there are right ways to get instant hot water without burning out your heater. Ask us.

What Does Rheem Error Code 11 Mean?

Rheem Code 11 means the unit tried to ignite and failed. No ignition, no flame, no hot water. This is the most-searched Rheem tankless code.

Lockout type: Hard.
Common causes: low inlet gas pressure, a closed or partially closed gas valve, an empty propane tank, a faulty or improperly wired gas solenoid valve, a failed igniter, or a damaged igniter wire. On converted homes, an undersized gas line that starves the unit at full fire is a classic root cause.
What you should do: check the honest basics — is your gas on? Are other gas appliances working? Beyond that, Rheem's diagnostic procedure for ignition failure involves gas pressure measurement and live electrical testing of the solenoid valves and igniter circuit. Call a professional.

A Southern California note: if your Code 11 appeared soon after a bargain tank-to-tankless conversion, the gas line is our first suspect. A tankless unit at full fire needs far more gas than the tank it replaced.

What Does Rheem Error Code 12 Mean?

Rheem Code 12 means the flame was lost during operation. The unit lit successfully, then the flame went out — so the unit shut down for safety.

Lockout type: Hard.
Common causes: marginal gas pressure that collapses under full demand, a dirty flame rod, damaged flame rod wiring, or exhaust recirculation disturbing the burner.
What you should do: intermittent flame loss can behave perfectly during a short test and fail only under sustained load — it is one of the trickiest faults to diagnose without instruments and experience. Professional service, always.

What Does Rheem Error Code 13 Mean?

Rheem Code 13 means improper combustion — found on indoor units. The unit is burning, but not burning cleanly.

Lockout type: Hard. ⚠️ Combustion codes are carbon monoxide territory. Take this one seriously.
Common causes: a fouled flame rod, a struggling blower motor, or blocked air intake and exhaust venting.
What you should do: do not keep resetting a combustion code. The unit needs its air path inspected end to end — intake, fan, burner, heat exchanger, exhaust — by a professional, the same day if possible.

What Does Rheem Error Code 14 Mean?

Rheem Code 14 means the overheat wrap — a thermal safety device around the heat exchanger — has faulted. This is a last-line safety system detecting heat where heat should not be.

Lockout type: Hard.
Common causes: blocked airflow, a damaged heat exchanger — or the Southern California classic: scale buildup creating hot spots inside the heat exchanger.
What you should do: never bypass or repeatedly reset an overheat safety. The overheating has a cause, and in our region that cause is usually scale. Professional diagnosis — and expect a conversation about descaling.

What Does Rheem Error Code 16 Mean?

Rheem Code 16 is an over-temperature warning — the water got hotter than your thermostat setting should allow.

Lockout type: Hard.
Common causes: scale-restricted flow through the heat exchanger, sediment, or short-cycling in a recirculation setup.
What you should do: like Code 14, this is heat out of control. Professional service — scale is suspect number one in our water.

What Does Rheem Error Code 24 Mean?

Rheem Code 24 means an operational switch has malfunctioned. Per Rheem's own troubleshooting manual, the first check is to disconnect the remote control and retry.

Lockout type: Control fault.
What you should do: this one is genuinely quick for a technician — the diagnosis separates a failing remote/switch from a failing board. Worth a call rather than a guess.

What Does Rheem Error Code 29 Mean?

Rheem Code 29 means a condensate drainage problem on condensing models — typically the condensate neutralizer or drain path is blocked, backing acidic condensate up into the unit.

Lockout type: Hard.
Common causes: a clogged or saturated neutralizer, a kinked or blocked condensate line, or a frozen drain during cold snaps.
What you should do: the unit shuts down to protect itself from condensate backup. Professional service — and a good moment to have the whole condensate system checked, since Code 92/93 (neutralizer life) travels in the same circles.

What Does Rheem Error Code 61 Mean?

Rheem Code 61 means the combustion fan motor has a fault. No fan, no safe combustion, no hot water.

Lockout type: Hard.
Common causes: a failed fan motor, damaged wiring, or debris restricting the fan.
What you should do: professional fan diagnosis and replacement.

What Do Rheem Error Codes 65 and 66 Mean? (The Water Valve Codes)

Code 65 means the water flow control valve has a fault, and Code 66 means the water bypass valve has a fault. These motorized valves regulate how much water moves through the unit and how it blends to your set temperature.

Lockout type: Hard.
Common causes: valve motor failure, damaged wiring or connections — and, in hard-water country, scale physically binding the valve mechanism until it can no longer move. This is the same failure pattern we documented from the manufacturers' own service sheets on other tankless brands, and Southern California water produces it on every brand we service.
What you should do: professional valve diagnosis and replacement — plus a serious look at descaling and scale prevention, because a valve seized by scale is never scale's only project. (You can look up your community's water hardness in our water quality library — we maintain profiles for 99 Southern California communities.)

What Does Rheem Error Code 71 Mean?

Rheem Code 71 means a gas inlet solenoid valve control fault — the electrical control of the valves that admit gas to your burner. (You may see this code defined elsewhere as a "communication" issue; Rheem's official troubleshooting documentation defines it as the gas inlet solenoid valve, and this guide follows the manufacturer.)

Lockout type: Hard. ⚠️ Any code involving the gas valve system is professional-only, full stop.
What you should do: Rheem's diagnostic procedure involves checking the valve's wiring harness and electrical values, then replacing the valve or the control board. Call a licensed professional.

What Does Rheem Error Code 72 Mean?

Rheem Code 72 means the flame sensing device has a fault — the flame probes are detecting flame when they should not be. The unit's flame verification system no longer trusts what it sees.

Lockout type: Hard.
Common causes: a fouled or damaged flame rod, wiring problems, or debris in the burner area interfering with flame sensing.
What you should do: flame rod service plus a combustion check — professional work. (A properly maintained flame rod is one of the quiet wins of an annual maintenance visit.)

What Does Rheem Error Code 76 Mean?

Rheem Code 76 means the unit and the remote controller have stopped communicating.

Lockout type: Communication fault — heating may continue in some cases, but you have lost control of it.
Common causes: loose or damaged remote wiring, or a failing remote or control board.
What you should do: professional diagnosis — the fix ranges from a connection repair to a controller replacement.

What Does Rheem Error Code 79 Mean?

Rheem Code 79 means the fan motor is drawing abnormal electrical current — the fan is running, but working harder than it should.

Lockout type: Hard.
Common causes: a fan motor beginning to fail, debris loading the fan, or wiring faults.
What you should do: think of 79 as Code 61's early warning sibling. Professional inspection now beats a dead fan in December.

What Do Rheem Error Codes 80 and 81 Mean?

Rheem Codes 80 and 81 mean gas cut-off failure — the unit tried to stop the flow of gas and could not confirm it stopped. Per Rheem's official troubleshooting documentation, the response involves testing all solenoid valves and, typically, replacing the gas control valve.

Lockout type: Hard — and this is a same-day service call. ⚠️ A gas valve that may not be closing fully is the most serious code in this guide. Do not attempt to operate the unit. If you smell gas: leave the area, do not touch electrical switches, and call your gas company from outside your home. Then call us.

What Do Rheem Error Codes 92 and 93 Mean? (The Countdown Pair)

Code 92 means the condensate neutralizer in your condensing Rheem is nearing the end of its life — it appears during operation. Code 93 means the neutralizer's life is over and must be replaced.

Lockout type: 92 is a soft warning; 93 requires service.
What you should do: treat 92 as your scheduling window. The neutralizer is a maintenance part — condensing units produce acidic condensate, and the neutralizer protects your drain lines from it. Replacing it on the 92 is a routine visit; waiting for the 93 just removes your flexibility.

What Does Rheem Error Code 99 Mean?

Rheem Code 99 means the unit cannot move enough air to burn cleanly — blocked ventilation causing imperfect combustion.

Lockout type: Hard. ⚠️ This is Rheem's most serious combustion code.
Common causes: blocked heat exchanger fins, obstructed exchanger flapper valves, a blocked vent termination, a dirty air intake filter, a struggling blower, or a failed combustion air sensor.
What you should do: do not repeatedly reset a 99 and do not run the unit. The entire air path needs professional inspection the same day. And if your home does not have carbon monoxide alarms near sleeping areas, fix that today regardless of your water heater.

What Does Rheem Error Code P1 Mean?

Rheem Code P1 means water flow dropped below the unit's minimum — under 0.66 gallons per minute for more than 5 seconds. Tankless units need a minimum flow to fire safely.

Lockout type: Operational — not a malfunction by itself.
Common causes: a barely opened tap, a clogged inlet water filter, low-flow fixtures below the activation threshold, or scale restricting flow.
What you should do: open the hot tap fully; if P1 persists at full flow, the inlet filter or flow path needs professional cleaning — and chronic P1s on a unit that used to work fine are often scale telling on itself.

What If There Is No Code at All?

A dead display usually means a power problem. Per Rheem's troubleshooting guidance: confirm the unit is connected to power and breakers are on, and that the inlet fuses are intact; a clogged inlet water filter or insufficient flow can also keep a unit from waking. Crossed hot/cold lines on new installations produce ghost behavior too. If power is present and the display is still dark, the issue is internal — call a professional. And never operate a unit that has been under water.

Frequently Asked Questions About Rheem Error Codes

How do I reset a Rheem tankless error code?
Many codes clear when the triggering condition ends (Code 00 resets when all hot taps close) or with a power cycle. But if a code returns after resetting, the fault is real — resetting is just muting the alarm. Gas codes (71, 80, 81) and combustion codes (13, 99) should never be reset-and-forgotten. When in doubt, call (877) 798-7487 and we will tell you over the phone whether your code can wait.

Are Ruud tankless error codes the same as Rheem?
Yes. Ruud is Rheem's sister brand, and Ruud tankless units are the same equipment under a different badge. Every code in this guide applies.

What is the most common Rheem tankless error code?
Ignition failure (Code 11) is the most-searched, usually tracing to gas supply, igniter, or solenoid valve issues. In Southern California we also see a steady stream of scale-driven codes — overheat faults (14, 16), seized water valves (65, 66), and flow problems (P1) on units that have never been descaled.

Is it safe to keep using my Rheem with an error code showing?
Usage warnings (00) and early warnings (92) allow continued operation while you schedule service. Hard lockout codes shut the unit down for your protection — never force a unit past them, and treat gas cut-off codes (80/81) and combustion codes (13, 99) as same-day calls.

Why does my Rheem keep showing Code 00?
Because something is running it continuously — most often a recirculation pump on a unit not designed for continuous circulation, or a plumbing crossover creating phantom demand. There are correct ways to get instant hot water at your fixtures; ask us about recirculation systems designed for the job.

Does hard water really cause Rheem error codes?
Yes. Scale creates the hot spots behind overheat codes, binds the motorized water valves, restricts the flow behind P1s, and shortens heat exchanger life. In our service area — some of the hardest water in California — annual descaling is the single highest-value hour you can spend on a tankless unit.

The Honest Truth: Most of These Codes Are Preventable

Look back through this guide and notice the pattern. Scale drives the overheat codes (14, 16), seizes the water valves (65, 66), and starves flow (P1). A dirty flame rod feeds the flame codes (12, 13, 72). Dust and blockage in the air path cause the combustion codes (13, 99) and stress the fan (61, 79). A neutralizer replaced on the 92 never becomes a 93.

Every one of those is addressed in a single annual maintenance visit: a professional descale of the heat exchanger, inlet filter and pre-filter cleaning, flame rod cleaning, condensate system check, and a full combustion and safety inspection. That is the entire reason annual tankless maintenance exists.

If your Rheem or Ruud is in Ventura County, Los Angeles County, Orange County, or the Santa Barbara area, ask us about THE Tankless Protection Plan — annual eco-friendly descale, pre-filter cleaning, flame rod cleaning, a free water test and heat exchanger inspection, priority scheduling, and a $0 diagnostic visit each year. It is how you make this entire article irrelevant to your household.

What Does Rheem Error Code Service Cost?

We believe in transparent pricing — it is written into THE Fair Price Guarantee on every invoice. The honest answer is that error code service depends entirely on what the diagnosis finds: a flame rod cleaning is very different from a gas control valve, and a descale is different from a fan motor. What we can promise: a flat diagnostic visit with the price told to you up front, a written quote before any work begins, and no surprises on the invoice — ever. Call (877) 798-7487 or build your project online, and you will know your number before we start.

Rheem or Ruud Showing a Code? We're Minutes Away.

THE Water Heater Company services Rheem and Ruud tankless water heaters across all of Southern California:

• Ventura County — 808 Calle Plano, Camarillo, CA 93012 (headquarters)
• Los Angeles County — 13615 Victory Blvd #108, Van Nuys, CA 91401
• Orange County — 630 S Grand Ave #109, Santa Ana, CA 92705

Serving Ventura County, Los Angeles County, Orange County, and the City of Santa Barbara — with same-day service available 7 days a week and phones answered by a live person 24/7/365.

Call (877) 798-7487 — THE Water Heater Company. Your Trusted Water Heater Authority.

Related Reading: More Guides from THE Water Heater Company

• Rinnai Tankless Water Heater Error Codes: The Complete Guide
• Noritz Tankless Water Heater Error Codes: The Complete Guide
• Navien Tankless Water Heater Error Codes: The Complete Guide
• Bradford White Water Heater Status Light Codes: The Complete Guide
• A.O. Smith Tankless Water Heater Error Codes: The Complete Guide
• Takagi Tankless Water Heater Error Codes: The Complete Guide
• Water quality profiles for 99 Southern California communities
• The State of Hot Water 2026 report

Sources

• Rheem, RTG-series Troubleshooting Manual (incl. RTG2-42) — official error code and diagnostic documentation
• Rheem, official tankless error code troubleshooting documentation (RTG series)
• Field experience: THE Water Heater Company certified technicians, Southern California service area