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Hot Water · Gas RepairGas Water Heater Repair
Gas water heater repair comes down to which tank you own. On an atmospheric tank the usual parts are the thermocouple ($150–$300) and the gas control ($400–$600); on a power-vent tank they are the igniter, flame sensor, pressure switch and blower. Most repairs land between $150 and $800 with the $90–$150 diagnostic folded in, and a tank under 8 years old is nearly always worth fixing.
Start at the top of the tank. A metal draft hood with a metal pipe rising to the chimney is an atmospheric tank, which lights from a standing pilot and has no plug. A plastic pipe leaving a fan housing is a power-vent tank, which usually has no standing pilot and lights electronically on each call for heat. The two share a burner and a relief valve and little else, so the parts list and the diagnosis are different jobs.
On an atmospheric tank the pilot flame heats a thermocouple, a probe that generates a few tens of millivolts to hold the gas valve open; newer controls with a blinking status light use a thermopile, a bundle of thermocouples that makes enough power to run the control's electronics. When either weakens, the pilot lights while you hold the button and dies when you let go. We measure the output with a meter before condemning it, because a pilot that is lazy, yellow or blowing off the probe gives the same symptom with a good part. If the millivolts are healthy and the burner still will not open, the fault is in the gas control.
Most tanks built in the last two decades have a sealed burner chamber, a design called FVIR, for flammable vapour ignition resistant. All the burner's air enters through a fine flame-arrestor screen under the tank, and that screen collects lint, dust and pet hair, fastest beside a dryer or a litter box. A clogged screen starves the flame: the pilot goes out, the burner burns yellow and soots the chamber, and on many models a thermal cut-off opens and shuts the gas. The repair is cleaning the screen and the base ring and resetting or replacing the cut-off, not a new thermocouple.
Every gas repair on a chimney-vented tank ends with a draft test. With the burner running for several minutes, the doors closed and the dryer, range hood and bath fans switched on, we hold a smoke source at the draft hood: smoke drawn up the hood means the flue is pulling, smoke rolling out means flue gas, and possibly carbon monoxide, is spilling into the room. Spillage usually traces to a blocked or oversized flue, or to a mechanical room that was closed in during a basement renovation with no combustion-air openings. That work has its own page, water heater venting repair.
Signs a gas water heater needs repair
- The pilot will not stay lit after you release the button, or goes out every few days
- The status light on the gas control is flashing a pattern instead of its normal slow blink
- Soot on top of the tank, a yellow burner flame, or scorch marks around the bottom access door
- Rumbling or popping while the burner runs, which is sediment boiling on the tank bottom
- Melted plastic rings on the pipe nipples at the top of the tank, or moisture on nearby pipes: flue gas is spilling at the hood
How it works
Tell us whether there is a pilot or a fan, what the status light is doing and how old the tank is. If you smell gas, do not relight anything: leave the house and call Enbridge Gas from outside.
Thermocouple or thermopile output, gas pressure at the control, igniter resistance, flame signal and pressure-switch operation are measured as the tank type requires. The flame-arrestor screen and the burner are inspected, and one price is put in writing.
The part is replaced, joints are leak-tested, the burner is watched through a full cycle and the hood is tested for spillage with the house fans running. If the tank has reached the end, we price a replacement on the spot, or you can request a quote.
Brands: We repair gas tanks from Rheem, Bradford White, A.O. Smith and John Wood, including tanks that were bought out of a rental.
Common questions
Why does my pilot keep going out on a newer tank?
On a sealed-burner tank the first suspect is air, not the thermocouple. Lint on the flame-arrestor screen thins the air supply until the pilot flame lifts or smothers, and a thermal cut-off may open as the chamber overheats. A downdraft in the chimney or a weak thermopile can do the same. Why a water heater pilot keeps going out lists the causes in order.
Is it worth repairing a 10-year-old gas water heater?
It depends on the part and the tank's condition. A thermocouple at $150–$300 on a dry, quiet 10-year-old tank is reasonable. A $400–$600 gas control on a tank that rumbles with sediment and shows rust at the fittings is money spent on something near its end. Past 12 years, or with any water at the base, we recommend replacing the water heater.
Can I clean the flame-arrestor screen myself?
You can vacuum the floor around the tank and the air openings at the base ring, and that helps. The screen itself sits under the sealed burner chamber, and reaching it properly means removing the burner assembly through a gasketed door that has to seal again afterward. A door that leaks defeats the safety design, so that part is technician work.
What does a spillage test tell you?
It tells you whether the exhaust is leaving the house. If the flue cannot overcome the pull of the dryer, range hood and bath fans, combustion gases spill from the draft hood into the basement. A tank that passes with the fans off and fails with them on needs more combustion air or a different vent, and it should not be left running until that is corrected.
My power-vent tank hums but never lights. Is that a gas problem?
Usually not. A blower that runs without ignition points to the air pressure switch, its tubing, a blocked vent termination or a cracked igniter, all of which sit ahead of the gas valve in the firing sequence. Those faults are covered on our power vent water heater repair page, along with how to read the status code.