How do you change a thermocouple on a gas boiler?

Asked By: Bryon Doyague | Last Updated: 6th June, 2020
Category: home and garden home appliances
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Replacing a Thermocouple
  1. Shut off the gas and electrical power to the furnace.
  2. Remove the furnace's access cover.
  3. If the furnace has been running, wait 30 minutes for the thermocouple to cool completely.
  4. Unscrew the nut that holds the thermocouple end fitting into the gas control valve, using an open-end wrench.

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Accordingly, how much does it cost to replace a thermocouple on a boiler?

Thermocouple Replacement - $20-$150 Calling a professional plumber to install a new thermocouple should only be up to $150. If you do the work yourself, you will only pay the price of the part which is about $20.

Also Know, are thermocouples universal? Universal Thermocouples. Universal thermocouples, as the name implies work on most water heaters. They are available online and in home supply stores for a reasonable cost. The length and the thread type are the two concerns when purchasing one.

In this way, how do you change a thermocouple?

How to Replace a Water Heater's Thermocouple

  1. Turn off the gas supply.
  2. Unfasten the three nuts that hold the thermocouple and the two gas tubes to the valve.
  3. Detach the thermocouple from the burner.
  4. Install the new one the same way that you removed the old one.
  5. Turn the gas back on and follow the lighting instructions on the water heater.

How do you change a thermocouple on a gas fireplace?

Place the new thermocouple in the same place your old one sat and close up the fireplace to conduct a test. Turn the gas back on and relight the pilot light. Give the thermocouple about 15 minutes to heat up and then turn on the flame to make sure it all stays functioning.

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How do you know if you have a bad thermocouple?

If you can't get the flame to light at all, and you're sure the gas is on, there's probably an obstruction in the pilot tube. If the flame lights and goes out when you release the gas control knob after holding it in for the recommended 20 to 30 seconds, that's the sign of a thermocouple malfunction.

How long do thermocouples last?

Thermocouples can last several years, but they don't typically last as long as the furnace itself. If the pilot remains lit, but the main furnace doesn't stay lit, it's time to replace the thermocouple. Replacement thermocouples are in stock at most hardware and home improvement stores.

Can you replace a thermocouple yourself?

If you are set on replacing the thermocouple yourself, here are a few things to keep in mind. Locate the thermocouple next to the pilot light and disconnect the unit by removing the copper lead. Unscrew the gas line connection nut AND bracket nut holding the thermocouple in place.

Why is my boiler not igniting?

Burner won't ignite: This is the most common cause of a boiler failing to provide heat. If the gas jets on the burner will not ignite, no heat will warm up the water in the tank. The trouble may be due to a failed electronic igniter/pilot light, or perhaps trouble in the gas line.

Are boiler thermocouples universal?


Universal Gas Thermocouple includes universal adapter fittings and is compatible with screw-in, push-in or clamp-type pilot burners. It is designed for gas furnaces and 30 mV systems. The element is built for reliability and long life.

How do you fix a bad thermocouple?

A burned out or broken thermocouple should be replaced. To replace a thermocouple: Step 1: Unscrew the copper lead and the connection nut inside the threaded connection to the gas line. Step 2: Under the mounting bracket at the thermocouple tube, unscrew the bracket nut that holds the tube in place.

How do you check a thermocouple?

Turn your multimeter to millivolts to perform an open circuit test. Place one of the test leads of the multimeter on the side of the thermocouple and the other to the end that enters the gas valve. Ignite a lighter, or other heat source with a flame, at the opposite end of the thermocouple.

What does a thermocouple look like?

The thermocouple looks like a piece of metal tubing smaller than a soda straw. To find it, first locate the gas control box. This is the box that the main gas line enters, where you turn the gas on in the furnace. The other end of the thermocouple sits in the flame of the pilot light.

What causes a thermocouple to fail?

Changes in temperature can cause regular expansion and contraction in metal, which will cause thermocouples to weaken over time. After enough time, metal fatigue can cause a thermocouple to break.

Can a thermocouple be cleaned?


If the Thermocouple is faulty it will cause the unit to shut down. How to clean? Remove Thermocouple from pilot assembly, using steel wool or emery cloth to lightly clean the tip removing any soot or build up that might have accorded due to an improper pilot flame.

Can you jump out a thermocouple?

Harley said: Bypassing the thermocouple would make it no more dangerous than any propane grill. It's not going to make it explode. The only thing it would prevent is losing a tank of propane into the atmosphere if the flame happened to go out because the valve wouldnt close.

Does the length of a thermocouple matter?

The length of a thermocouple has no effect on its measurement accuracy or its ability to transfer the signal to the instrument. In other words, thermocouples do not experience “voltage drops” or power loss along its length as a high current power line might possess.

Why does my gas burner keep going out?

The most common cause of this is dirty or blocked burners, which is the part that you can easily take off to clean. All the small holes on the burner should be clean and clear, if not then even a partial blockage can lead to the thermocouple not getting enough heat and, the burner won't stay lit.

How does a thermocouple work?


A thermocouple is a sensor used to measure temperature. Thermocouples are made with two wires of different metals, joined together at one end to form a junction. As the temperature changes, the two dissimilar metals begin to deform, causing a change in resistance.

How does a thermocouple work on a gas valve?

The thermocouple in a gas furnace is designed to keep the gas valve open through its electric voltage. If the pilot light goes out, the loss in heat causes the voltage between the two pieces of metal to drop, and this shuts the valve and reduces the combustion risk.

Can a thermocouple leak gas?

Without a thermocouple, it will seep tiny bits of gas into the combustion chamber of the device. In a few hours, it can leak enough gas for a small explosion, probably just enough to shorten your eyebrows.