Water Heater Thermocouple Replacement Cost

The thermocouple is a small safety sensor on gas water heaters. It senses the pilot flame and shuts off the gas if the flame goes out. When it fails, the pilot will not stay lit and the heater stops making hot water.

Cost

Most of the price is the service call and labor. Plumbers charge about $45 to $150 per hour (HomeGuide), and HomeGuide notes minimum service call fees of $50 to $200.

Signs of a failing thermocouple

• The pilot lights but goes out when you release the pilot button.
• The pilot keeps going out every few hours or days.
• The heater stops producing hot water while the gas supply is on.

A pilot service call alone costs $50 to $150 (Angi), so if the pilot simply blew out, relighting it may solve the problem.

Related gas repairs

If the thermocouple is fine but gas still does not reach the burner, the gas control valve may be the problem. See water heater gas valve replacement cost.

Repair or replace the heater?

A thermocouple is one of the cheapest repairs on a gas water heater, so it is usually worth doing even on an older unit. If the tank is leaking or more than 10 years old with several problems, compare with gas water heater replacement cost.

What a thermocouple does

On a gas water heater with a standing pilot, the thermocouple is a small metal probe that sits in the pilot flame. As long as the flame heats it, it produces a tiny electrical current that keeps the gas valve open. If the pilot goes out, the current stops and the valve shuts off gas for safety. Some newer heaters use a thermopile or a flame sensor instead.

Signs of a bad thermocouple

• The pilot lights but goes out as soon as you release the pilot button.
• The pilot keeps going out on its own.
• No hot water even though gas is on.

What the repair involves

The technician turns off the gas, removes the burner assembly access cover, disconnects the thermocouple from the gas valve, replaces it, relights the pilot and checks that it stays lit and the burner fires.

What affects the price

Thermocouples are among the cheapest water heater parts, so the price is mostly the service call. Sealed-combustion heaters, where the burner assembly must be removed as a unit, take longer. If the real problem is a dirty pilot, a bad gas valve or a draft, more work is needed.

Doing it yourself

On many older heaters, thermocouple replacement is a common DIY repair. On sealed-combustion units and heaters with flame sensors and electronic controls, it is better left to a professional. Any time you are working on a gas appliance, check for leaks afterward.

In Texas

Garage water heaters in Texas can have pilots blown out by drafts from an open garage door, which can look like a thermocouple problem. A technician can tell the difference.

Thermocouple, thermopile or flame sensor?

Not every gas water heater uses the same flame-safety part:

• Thermocouple: found on many standard pilot-light heaters. It produces a tiny voltage when heated by the pilot flame, which holds the gas valve open.
• Thermopile: a bundle of thermocouples that produces more voltage. It is used on some gas valves with electronic controls.
• Flame sensor: found on heaters with electronic ignition, including many power-vent and newer models.

Knowing which one your heater uses helps the technician bring the right part and can shorten the visit. The model number on the label tells you.

Common reasons the pilot will not stay lit

A failed thermocouple is the classic cause, but not the only one. A dirty or clogged pilot tube can produce a weak flame that does not heat the thermocouple enough. A thermocouple that is not positioned correctly in the flame can also cause the problem. On newer heaters with a flammable vapor sensor, the sensor may shut the heater down if it trips, which sometimes points to vapors near the heater or a dirty air intake screen.

How the repair is done

The gas is turned off at the heater's valve, and the burner assembly is reached through the access panel. On many heaters the burner, pilot and thermocouple come out together. The old thermocouple is unscrewed from the gas valve and the new one is fitted, positioned correctly in the pilot flame and tightened by hand plus a small turn. The assembly is reinstalled, the pilot is relit and the burner is tested.

On sealed-combustion heaters, the inner door gasket must be in good condition when the assembly goes back in. A damaged gasket should be replaced, because it keeps the combustion area sealed.

Safety notes

• If you smell gas at any point, stop, leave the house and call the gas utility.
• Keep paint, gasoline and solvents away from a gas water heater.
• After any repair, watch the burner flame. It should be steady and mostly blue. A lazy yellow flame or soot means the heater needs servicing.

How long a thermocouple lasts

A thermocouple sits in the pilot flame every hour the heater is on, so it slowly wears out. Many last for years, but a pilot that has been going out more often is a sign the end is near. Because the part is inexpensive, many technicians replace it during any pilot-related service call on an older heater rather than coming back later. If the new thermocouple fails again quickly, the cause is usually something else: a dirty pilot, poor combustion air or a draft problem that keeps blowing the pilot flame away from the tip. Fixing that cause saves you from paying for the same part again.

Before you call

Try relighting the pilot by following the instructions on the label. If it lights but will not stay lit after you release the knob, the thermocouple is the likely cause.