Malfunctioning Thermocouple in Water Heaters: What are its Implications?

May 1, 2019

The notion that an appliance thermocouple can malfunction constitutes something of a worry. Let’s clarify the matter so that you can understand why this possibility is so alarming. As a general rule, at least in gas-flamed systems, thermocouples are designed to shut off the gas if the pilot light goes out. Otherwise, they’re never used. They just hang out opposite the pilot flame, waiting for it to fail.

Pilot Flame Failure: Weighing the Repercussions

Normally, there’s not a lot to worry about. If a pilot flame is extinguished, the appliance’s safety feature makes sure the gas shutoff valve initiates. That’s the thermocouples job, to actuate the gas shutoff. Let’s assume, just for the purposes of this demonstration, that a malfunction is stopping the thermocouple from sensing the loss of the pilot flame’s heat. With the gas still flowing, the combustion chamber fills with gas. Now, should a small spark occur anywhere near the water heating unit, an explosion is triggered. Lives are at risk until that bi-metal strip is repaired.

Maintaining Water Heater Thermocouples

It’s the simplicity factor that makes this heat sensing assembly such a reliable safety feature. Two different types of metal are joined together at one end. With a thermal energy envelope enveloping those contact points, the electrical current flowing through the metals varies. Essentially, this is a crude but reliable temperature sensing circuit. It rarely fails, but that doesn’t mean it never malfunctions. As such, it needs to be checked, to be maintained by a competent heating engineer. So far so good, that preventative maintenance schedule should eliminate all potential thermocouple-related system glitches. However, nothing can be left to chance, not when a defect could cause a life-threatening explosion. If a glitch in the bi-metallic component does occur, it needs to be replaced, promptly and without hesitation.

Diagnosing Thermocouple Malfunctions

It’s not difficult to check out a faulty strip of failing metal. There could even be some visual evidence of trouble, such as a blackened tip. Damaged in this way, the two different metals conduct electricity less predictably. A check with an electrical multimeter confirms the fault, and that new component is substituted. The old component goes in the bin, then it is back to the six-month or annually conducted maintenance checks.

There’s no way this point can be overemphasized: damaged water heater thermocouples may allow gaseous build-ups to accumulate. With the gas filling an appliance’s combustion chamber, a small spark could cause a deadly accident. To eliminate the explosive potential, do have a service engineer check that bi-metal strip regularly. It’s a simple gas shutoff actuator. For all that, it’s also one of the most important safety features on a gas-fuelled water heating system.

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