What Is a Thermopile on A Water Heater?

A thermopile is a piece of equipment that transforms heat energy into electrical energy. It is made up of numerous thermocouples that are commonly linked in a series or, less typically, in parallel.

This type of gadget operates on the thermoelectric effect, which generates a voltage when its different metals (thermocouples) are subjected to a temperature differential. Thermopiles are composed of a bunch of different thermocouples.

The way they work is through measuring the temperature differential from the junction point, to the point where the thermocouple output voltage is being measured at.

You have the option to connect a bunch of different thermocouples inside of a junction on each side of the resistance layer. The overall output resulting from the junction of thermocouples will end up being the voltage that is proportionate to the temperature difference throughout the resistance layer.

difference between thermocouple and thermopile

How Do I Know If My Thermopile Is Bad?

To figure out if your thermopile is bad, you’ll want to get a multimeter to test it with. Connect the TH/TP contact to it to see how much thermopile voltage is flowing through it. Before you go ahead and do the test, you’ll want to make sure your pilot light has been on for over two minutes.

Locate the primary gas control valve. Then, locate the thermopile sensor, and finally, the electric contacts which are labeled TH/TP and TP on the valve. You may find these in your manufacturer’s manual.

Place one of the multimeters leads on the TP/TH terminal and the other on the TP terminal.

It should register 300 millivolts on the multimeter. If it reads just under 300 millivolts, it might be the reason your gas fireplace isn’t working, and you should consider replacing it at that point.

How Do You Fix a Thermopile?

The first step to beginning to fix a thermopile is to diagnose the problem in the first place. You’ll want to have a multimeter handy to see what the root of the problem is.

If your thermopile is reading over 300 millivolts of voltage, then your thermopile is still doing alright. If the reading you get on your multimeter is under 300 millivolts, then you should start thinking about replacing it.

You’ll also want to test out your thermocouple to see if that’s causing any issues. If the thermocouple is still in good shape, it’ll typically show over 25 millivolts. If it reads under 25 millivolts, then you should replace it.

You won’t want to go out and replace your thermopile the second you figure out it isn’t functional. First, go and see if you can clean their probes before heading to the store. To clean the thermopile, you’ll want to shut off the gas supply if there is one. Get a stainless-steel brush and some fine-grit sandpaper and start scrubbing the soot and debris off of it.

Once you’re done cleaning the thermopile, you can go ahead and test it again. Ignite the pilot light back up and then test it out again with your multimeter.

If cleaning it didn’t do the trick, then you can go and replace it.

What Is the Difference Between Thermocouple And Thermopile?

The main difference between a thermopile and a thermocouple is that a thermocouple is a thermoelectric device, whereas a thermopile is a device that will convert electric energy into thermal energy.

Thermocouples have two metals that are connected to form a series. One of the junctions is blackened to absorb radiation.

A thermocouple is thinner than a thermopile and has one end that’s pointed. The way a thermocouple works is by measuring the difference in temperature from the connection point to the output thermopile voltage point.

How Much Does It Cost to Replace A Thermopile?

The cost to replace a thermopile isn’t that much for the part itself, but if you’re calling a plumber to come out and do the replacement, that’s where things start adding up. Plumbers usually charge an upfront fee just to make house calls, and the labor is extra on top of that.

For the part itself, you’re looking at around $5-10. But after the plumber is done with the work, you might be looking at up to $150 when labor is included.

How Do You Test A Thermopile?

Testing a thermopile will be like testing out a thermocouple. Thermopiles are designed to produce nearly 750 mVDC, and if you get a reading of 325 mVDC, then that’s still within the acceptable range if the switch is located near the appliance.

To test out the thermopile, you’ll have to take off the leads from the TP/TH and TP terminals. After that, put the leads from the multimeter onto the wire terminals. Check the reading and see what your number is.

thermopile in locomotive engine

How Much Is a Thermopile?

A thermopile doesn’t cost too much. You’ll typically be paying between $5 to $10 for a new one. If you can’t install it yourself, labor will be where the costs can accumulate faster.

What Causes A Thermopile To Go Bad?

There are a couple of things that can cause a thermopile to go bad.

Poor Gas Pressure

If the pressure isn’t set correctly, things won’t work very well. If you’re not aware of how to set the pressure yourself, you can contact a technician to take a look at it and show you how.

Gas Valve Is Faulty

It isn’t usually the cause of a thermopile going bad, but it can be part of the problem if other things are ruled out.

Moisture Build-Up

If there is any moisture in the lines, that can cause some issues in the drip loop.

Clogged Ports

When anything gets clogged, it doesn’t function how it should, and the same goes for this situation. You’ll want to clean the ports on a routine basis to reduce the chances of dealing with dirty ports.

How Much Voltage Should a Thermopile Put Out?

A fully functional thermopile should be producing electrical energy between 25 to 35 millivolts.

Thermopiles might be a complicated subject when you first investigate it, but after reading about the ins and outs of it, it becomes easy to understand how they function when used with either a gas furnace or a heater.

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