How Does a Water Heater Work?

A tank water heater keeps 40–75 gallons hot around the clock inside an insulated, glass-lined steel vessel. Cold water enters through the dip tube and drops to the bottom, the gas burner underneath heats it, exhaust rises through a central flue that transfers even more heat on the way out, and hot water floats to the top where the outlet draws it the moment you open a tap. A sacrificial anode rod corrodes instead of the tank, and the T&P relief valve stands guard as the safety of last resort — explore every one of those parts in the 3D model above.

A tankless water heater stores nothing — it heats water only while a tap runs. A small turbine flow sensor detects moving water and tells the control board to spin up the combustion fan and light the modulating burner rack, which throttles its flame to match your exact demand. The water picks up its full temperature rise in the seconds it spends snaking through the copper heat exchanger, so hot water never runs out, but the unit must be sized correctly for your home's peak demand — that's why professional tankless sizing matters more than any spec sheet.

The anode rod is a magnesium or aluminum rod hanging inside the tank that corrodes on purpose — its metal gives up electrons more readily than steel, so corrosion eats the rod instead of your tank. It's typically consumed in three to five years (faster in softened water), and once it's gone the tank itself starts corroding. Replacing a spent rod costs a fraction of a new water heater, which is why we check it during every $99 flush visit.

That sound is almost always sediment — a blanket of hardness minerals that settles on the tank bottom in Southern California's hard water. Water trapped underneath it flashes to steam when the burner fires, and the pops and rumbles you hear are those steam bubbles collapsing. The sediment also insulates the water from the flame, so the tank recovers slower and the steel bottom overheats. An annual flush clears it before it hardens into a permanent problem.

A typical tank water heater lasts about 8–12 years, and a well-maintained tankless unit often reaches 15–20 — the difference comes down to water quality and maintenance. Anode replacement and annual flushing stretch a tank's life; annual descaling does the same for a tankless heat exchanger. Age matters most at the decision point: once a tank is past ten years, money spent on major repairs is usually better put toward planning the replacement on your schedule instead of the tank's.

Immediately, for anything involving gas, combustion, or venting: gas smells, soot, scorch marks, a pilot that repeatedly drops, or exhaust spilling at the draft hood. The same goes for water leaking from the tank vessel itself (that's a failed tank, not a repair) and a T&P relief valve that drips or has ever been capped. Resetting a tankless error code once is fine — needing to reset it weekly is a diagnosis visit. Our specialists answer 24/7 at (877) 798-7487, and same-day repair is the norm, not a rush fee.