Signs and Symptoms of a Bad Hot Water Heater Thermocouple

How Thermocouples Work

In the burner section of a gas water heater, the thermocouple is located near the pilot light. It consists of two metal wires that are welded together at the ends and coated in a protective metal case. At one end of the thermocouple is a junction that is connected to the pilot assembly. At the other is a metal probe that sends an electrical current to the gas valve when its probes are heated to a certain temperature. This alerts the valve that the pilot is lit, and the valve may send gas to the burner if the thermostat indicates it is needed. If it senses the pilot has gone out, it tells the gas valve to close until the pilot is lit again.

Often the first sign of any water heater problems is that you have no hot water supplied to your faucets. Sometimes even a reduced amount of hot water can indicate that there may be an issue. Check the thermostat on your water heater; if it is below 120 degrees Fahrenheit, then turn it up to this temperature. If you still have no hot water, or reduced amounts of hot water, the thermocouple may be malfunctioning.

A visual inspection of your water heater’s thermocouple may be enough to determine whether it is functioning or not. If the tips on the thermocouple probe have deteriorated or are damaged, then it’s time to replace it. If the probe has a white substance coating it, this is carbon, which can prevent the probe from getting enough heat to send an alert to the gas valve. Typically carbon can be cleaned away, and you don’t have to replace the thermocouple. Sand it gently with emery cloth to remove the carbon, and it should work as it did before.

One of the main signs of a bad thermocouple is when your pilot light goes out and the burner on your water heater won’t light. You can test the thermocouple by pressing the pilot button on the gas control valve to relight the pilot. Hold it for about 30 to 60 seconds and then release the button. If the pilot light goes out after you release it, then your thermocouple is bad. However, if the pilot will not light at all, your problem is with the gas flow to the water heater or with the gas valve, and not your thermocouple.