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Thermocouple Problems and Troubleshooting

Thermocouples are self-powered devices consisting of two standard conductors made up of different materials (usually metal alloys) which produce a voltage at their point of contact. The voltage generated is dependent on the difference in temperature of the junction to the other parts of the conductor. Hence thermocouples are an affordable and efficient temperature sensor for measurement and control. Usually issues faced by these devices could include malfunction, inaccurate readings, and so on. Listed below are a few questions answered by the Experts on issues related to thermocouple problems.

My thermocouple has a transistor attached to it and the pilot light will not remain on. Do I need to change the pilot assembly and do I require the same transistor?

Usually a thermo is replaced when the pilot light is re-lit and the light goes out when the pilot light button on the gas valve is released. The reason for the lights going out could be due to clogged air intake vents. If the vents are clogged, turbulence is caused when the main burner shuts down putting out the pilot. Check for clogs at the pilot orifice by passing a thin wire through it even if you can see daylight at the other end. Sometimes if the “Piezo” igniter is not working, replacing the pilot assembly may be required. The transistor is a cut out device. A tripped transistor usually indicates that you need to change the pilot assembly.

My LPG water heater needs the thermocouple to be changed. How do I do it? ?

Before you begin, turn the gas off. Then locate the thermocouple which is usually the tube running back to the valve. Separate the burner from the water heater. Loosen the screws which keep the thermocouple in place and take the unit out from its holder at the flame. Then position the new thermocouple in the flame, similar to the way the old one was fixed. The flame should just be able to make contact with the machine. The main purpose is that the heat from the flame should allow the thermocouple to keep the valve open. Also the cap tube of the thermocouple should be the same diameter as before while the tube could be shorter.

How can I accurately check or test a thermocouple?

To read or test a thermocouple, you would need a multimeter which reads millivolts. Hold down the pilot button on the gas valve in order to allow the pilot to remain lit, leaving the thermocouple installed. Connect one lead to the copper wire on the thermocouple and the positive lead to the tip that connects to the gas valve. The reading recorded should be at least 10 MV. The readings could vary since the connections may not be very strong and the readings are only in millivolts.

What is the procedure for installing a thermocouple?

There will be a nut at the end of the spaghetti size copper tube from the hot side of the thermocouple where it screws in to the gas valve. Unscrew this nut counter clockwise. Then locate the round collar type clip which holds the hot end of the thermocouple into the pilot light. Detach it, remove the entire part and take it to the hardware store to buy a new one. Once you have got a thermocouple which matches the old thermocouple or one that has various clips that can be manipulated to fit correctly, poke the hot end to the pilot light assembly in place of the old one. Follow the instructions on the package and finally screw the other end to the gas valve. In most cases it would turn in the opposite direction of the usual thread. Screwing it in would require you to turn it counter clockwise and make sure it is secure using no more force than you usually would on a four inch long wrench.

How do I identify the thermocouple part number?

Thermocouples are similar to light bulbs in some ways. There is no conspicuous or useful part number available. What you would need to do is remove the old thermocouple—it will be a left hand thread so make sure you unscrew accordingly. Take the thermocouple to a hardware store for a replacement which is the same size on each end and same length or longer.

Thermocouples are essential for displaying the temperature especially in a residential environment. Common problems that may occur with it can sometimes be fixed by a layman with an idea of the mechanics behind it. There may be other major problems which should be tackled by professionals. If you are wondering how to resolve the issue you may be facing with your thermocouple, contact Experts for help, information or guidance.

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