Temperature Sensor Trips - Repair Tips

Find out the reasons why the temperature sensor inside the thermocouple of the gas water heaters trips and how to fix it.

This article is about gas water heaters equipped with the FVIR or flammable vapor ignition resistant system. The FVIR system is found on all today’s water heaters, either from Rheem, AO Smith, Bradford White, or any other manufacturer. Some of the elements included in the system are the pilot light, thermocouple, and flame arrestor.

We will explore 4 reasons why the temperature switch inside the thermocouple trips causing the water heater to turn off and how can you fix it:

Lack of air. The gas water heater is not getting enough combustion air, and that causes the burner flame to get lazy and wander around. You can easily check the flame status through the vision port located at the bottom of the unit. The solution to this problem is to provide enough fresh air for the water heater and every gas-powered unit inside the same room. If the unit is installed inside the closet or utility room, the provisions on the external wall or door to the next room should be big enough to provide a continuous supply of air.

If you know that lack of air is an issue, you can temporarily fix the problem by keeping the door wide open so enough air gets in. For the long-term solution, ensure that the openings and location are per the manufacturer’s instructions or codes.

Also, check for the negative pressure, which can cause the downdraft of the flue gases that cannot exit. This condition occurs when the water heater is installed in the same room as other gas-powered appliances, and there is a leak in its venting system.

No draft. A venting system must be done per codes and water heater manufacturer. The venting must have a proper length with no sags and damages, also no restrictions or obstructions along the vent pipe. Use the match and put it at the inlet to the draft hood to check are the flue gases are properly transferred out or not.

Dirty flame arrestor. The flame arrestor is designed to keep the flammable vapors inside the combustion chamber. If the flame arrestor is dirty due to the dusty environment, lint, or dirt, the flame inside the unit will become lazy and increase the temperature inside, which will cause the temperature switch inside the thermocouple to trip. Perform the periodic cleaning of the flame arrestor by using the soft brush and vacuum cleaner.

The flammable vapor event occurred. How to recognize the accident… the flame arrestor has been discolored due to the extremely high temperature inside the combustion chamber, causing the situation when there is no repair, so the water heater must be replaced.

The air pressure switch is the element used on all power vent models, and it checks that there is proper venting/removal of the products of combustion.

It verifies that the blower is running correctly, which is not a case when the vent/exhaust pipes are blocked or very long. The switch activates in response to the pressure (ex. pressure change due to blockage), opening or closing the circuit sending the impulse to the circuit board for further action.

The circuit must be closed at all times during the heating cycle. Open contacts mean that there is no flow of electricity so that the unit won’t run.

The air pressure switch has a flexible diaphragm that divides the body into two air chambers (one is vented to the atmosphere) with its ports, so when the diaphragm moves, it activates the switch contacts.