Temperature Sensor Trips

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

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

We will explore 4 reasons why the temperature switch inside the thermocouple trips, causing 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 for 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 continuous supply of air.

If you know that lack of air is an issue, you can temporary 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 manufacturer’s instructions or codes.

Also, check for the negative pressure which can cause the down draft 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. 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 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 dirty environment, lint or dirt, the flame inside the unit will become laze 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.

A 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.

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