The thermocouple is a safety device attached to gas boilers. If the pilot flame goes out on a gas boiler, the potential exists for gas to pour into the air. This creates a health and fire risk. The thermocouple shuts the gas valve off if no heat is coming from the pilot light. This is a fail-safe strategy to protect many gas-heating appliances. Testing the thermocouple might alert you to problems with the heating system in a home. This straightforward technique can keep the boiler running safely throughout the winter months.

A lighter simulates the pilot light when testing the thermocouple.

Step 1

Turn off the gas going to the boiler. The method involved in turning off the gas will depend on the boiler unit and the design of your home. Once the gas is off, wait at least 15 minutes to allow the unit time to cool down.

Step 2

Use a screwdriver to remove the access panel screws. Pull the loose panel off the unit to remove it. Set the panel to the side.

Step 3

Remove the thermocouple from the boiler. Take a wrench and loosen the bracket nut on the end of thermocouple. Loosen the nut at the end of the gas valve with the wrench. Pay attention to the location of the thermocouple connections. You will want to reinstall the part in the same place.

Step 4

Set a voltmeter to read within the millivolt range. Connect the voltmeter to the thermocouple wires that sit at the valve end.

Step 5

Hold the thermocouple with needle-nose pliers and position it over the flame of a lighter. This will simulate the pilot light flame and should produce a reading on the voltmeter. If there is no jump on the meter, the thermocouple is faulty. However, if the voltage increases, the thermocouple works fine.

Step 6

Let the thermocouple cool and replace it or install a new part. Reverse the steps taken in removing the piece.

Step 7

Turn the gas back on and light the pilot flame. Replace the access panel and secure it with the screws.