Water Heater Thermocouple

Thermocouple Buyers
            Guide

Standard style

Also called universal water heater thermocouple. It screws into the bottom of the gas valve and a probe on the other end slides into a holding bracket near the pilot light. It looks like a piece of copper wire ( see pic. below).

This thermocouple has a right handed thread. Turn right to tighten left to loosen. Universal thermocouples come in lengths from 15 to 36 inches. An 18 or 24 inch will suffice for all residential water heaters using universal kits.

Almost all older waters heaters and many of the newer style units with a sealed burner compartment and a viewing window will use this thermocouple.

If you want to use an exact replacement length just remove your old one and measure it.

TCO style

Thermal Cut Off style has a resettable thermal shut off switch integral into the thermocouple. In the event of a flash fire or blow back from the burner the TOC will shut down gas flow to the burner and pilot.
In case of a shut down the TOC should reset itself after it cools down and allow you to relight the pilot.
The TOC switch looks like a watch battery. You will only find the TOC on newer style water heaters with seal burner compartments.

TOC non-resettable style

These thermocouples have a tiny TOC build inside the tube. They look similar to a standard one except the diameter is larger about midways of the tube.
When these TOC's switch off they will not reset and must be replaced.

Whirlpool Water Heater Thermocouple

Some of Whirlpools older model water heaters were built with a left-hand thread thermocouple.
Turn to the left to tighten, right to loosen. These are no longer available.

Lowe's home improvement sells a Manifold Door Assembly for Whirlpool water heaters. It comes with a thermocouple attached. Cost is about $35.00. Their website Lowes.com

You can also purchase one directly from Whirlpool at about the same price. Their costumer service number 1-866-698-2538.

These water heaters were built by American Water Heater Co. They have a lot of "how to" replace parts guides for their water heaters. Follow the link below.

American Water Heater Co.

How thermocouples work

A pilot thermocouple sends a tiny electrical current to the gas valve when the probe is heated to a certain temperature.
This electrical current tells the gas valve that the pilot is lit and its ok to send gas to the burner if the thermostat calls for it.

To check a water heater thermocouple press the pilot button down on the water heater gas control valve. Light the pilot. If after holding the pilot button down 30 to 60 seconds the pilot light goes out when you release the button, the thermocouple is most likely at fault on older units. The TOC or air flow could be the problem on newer units with a pilot light viewing window .

If the pilot does not light at all the problem is gas flow, gas control valve, TOC tripped.

The most common thermocouple problems

The tip on the thermocouple probe has deteriorated.
Lack of air (oxygen) on seal burner water heaters.

Thermocouple Repair

If the probe looks white this is carbon build up. It can keep the probe from getting hot enough to send a signal to the gas valve. Sand it with emery cloth and relight the pilot. It should work for a while but keep a new thermocouple handy.

The thermocouple probe must be in the pilot light flame.

The thermocouple must be screwed into the gas valve tightly.

Check the pilot thermocouple tube for kinks.

Water heater thermocouple replacement

Thermocouple replacement is a simple process. If your handy with tools you shouldn't have any problems.
Always follow all safety rules when working around gas.

A universal water heater thermocouple can be found at most hardware stores.

In the guide below I've removed the burner assembly so you can see how the thermocouple is positioned next to the pilot.

How To Replace A Thermocouple

This is a universal thermocouple kit.

It will fit most water heaters.

The pic on the left is the water
heater burner assembly removed
from the water heater.

The thermocouple is located next
to the pilot head.

Turn the gas off to your water heater.

Set the temperature control knob
(on the gas control valve)to the
lowest setting.

Turn the on/off pilot control knob
to the off position.

Remove the outer and inner burner assembly access panels.

Remove the thermocouple from the gas control valve using a 3/8 in.
end wrench (see picture above).

Reach into the burner compartment and pull the thermocouple out of
its holder.
A hard tug should do it.

If you can't pull it out, skip the next step and scroll down this page for
instructions to remove the burner assembly.

Got the thermocouple out? Good.
To install the new one, use a
flashlight so you can see and
slide the probe into place.

The tip of the probe should be
1/8 to 1/4 in. pass the pilot head.

Attach the other end to the gas control valve.

Remove the Burner Assembly

Ok, you've disconnected the
thermocouple from the gas control
valve but can't get it freed from the
burner assembly.

You'll have to remove the water heater burner.

Using a 7/16 in. end wrench
disconnect the pilot supply tube
from the gas control valve.

Remove the burner supply tube
using a 3/4 in. end wrench or
an adjustable wrench.

Remove the burner assembly from
the water heater.

Now you can remove the
thermocouple with a pair of pliers.

Slide the new water heater
thermocouple into place. Position
the tip of the probe 1/8 to 1/4 in.
pass the pilot head.

Reinstall the burner assembly

Be sure that the end of the
burner assembly fits into the slot
that holds it in place (see picture).

When your finished check all
connections for gas leaks.

Related pages

Light the pilot on older style water heaters.

Light your pilot light on FVIR style units.

Gas water heater troubleshooting.

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