A failing thermopile prevents the safe and consistent operation of a gas appliance, like a fireplace or water heater. Because a thermopile generates the millivoltage needed to open the main gas valve, common symptoms include:
Thermopile Check While flame is on, put alligator clips that are attached to the leads of the millivolt meter to the two leads from the thermopile. Turu pilot on. Turn burners off. Readings should be between 350 mv.
Thermopile Lifespan
A thermopile generally lasts 5-7 years, sometimes longer if the pilot flame is strong and clean. Thermopiles run hotter and generate more power, so they slowly weaken as the internal junctions degrade. If the system sits unused for long periods, the lifespan varies more.
If the Thermopile is overheated (i.e. the pilot flame applied to it is too high) this will cause the cold zone (the lower end of the Thermopile) to be too warm, leading to premature failure. Up to the time of outright failure, you'll probably see the thermopile fail, and then just cool off and sit there doing nothing.
This can restore proper flame sensing and resolve pilot light won't stay lit, furnace ignition issues, and gas furnace safety sensor problems. However, if cleaning doesn't fix the issue, the thermocouple may be worn out and require replacement.
If the thermocouple doesn't look too dirty, you can try cleaning it without removing it:
DIY Maintenance Tips
Regular cleaning of the thermocouple is recommended at least once a year. If signs of malfunction appear, consider cleaning it more often. Here are some tips to prevent dirt buildup: Keep the area around the water heater clean.
Inconsistent Water Temperature: Fluctuating temperatures can indicate a failing thermopile. No Hot Water: If your heater won't turn on, the thermopile may not be generating the necessary voltage. Frequent Pilot Light Outages: A thermopile issue can cause the pilot light to extinguish often.
A healthy pilot flame should be a crisp, steady blue, engulfing the top third of the thermocouple. A weak, yellow, or wavering flame often indicates a dirty pilot orifice or a gas supply issue, preventing the thermocouple from getting hot enough to function.
Replacing a thermocouple is a relatively easy fix that can take less than two hours. This guide reviews how to replace a thermocouple to ensure gas appliances stay in good working order, as well as how to relight a pilot light.
If a higher value of voltage is required, a thermopile, which is manufactured from several series-aiding connected thermocouples, can provide voltages of typically 250 DC millivolts or 750 DC millivolts.
The post or thermocouple may occasionally glow red, which is normal for the unit as long as the pilot flame is covering it. Always glows red. When the spark igniter and thermocouple are covered by the flame, then it will indeed function. I wouldn't be too concerned unless the unit fails to spark or ignite.
Both a thermocouple and a thermopile convert heat into electrical energy using the same principle (the Seebeck effect). However, a thermopile is simply multiple thermocouples connected in series. The fundamental difference is that thermocouples are primarily safety sensors generating low voltage, while thermopiles generate higher voltages capable of operating system controls.
How can you tell if a thermostat is bad?
To test a thermopile, you will need a multimeter that can read Direct Current (DC) millivolts. There are two methods to test it: the Open Circuit Test (raw generating power), and the Closed Circuit Test (voltage under load, the most accurate method).
Steps for Furnace Thermocouple Cleaning
On average, professional replacement costs can range from $100 to $300 or more, depending on these factors. 3.
Check connections at both the controller and the thermocouple. Tighten any loose terminal screws (don't over tighten to the point of wires being smashed)
A failing thermopile prevents the safe and consistent operation of a gas appliance, like a fireplace or water heater. Because a thermopile generates the millivoltage needed to open the main gas valve, common symptoms include:
A thermopile typically lasts 5 to 7 years, though they can reach 10 to 15 years with optimal maintenance and a clean, steady pilot flame.
To check the millivolts on a thermopile, use a digital multimeter set to DC millivolts. With the pilot light on, test the raw output by disconnecting the wires (Open Circuit test) or check the voltage under a load (Closed Circuit test). A healthy thermopile typically produces between 325 mV and 850 mV.
You will want to clean the thermocouple with a piece of emery cloth or high grit (1000) sandpaper. This may resolve the issue. Another issue that could be causing this is the connection point between the thermocouple lead and the gas valve.