If your furnace keeps shutting off, the culprit may be the ignitor. Modern gas furnaces work with electric ignitors, unlike older furnaces that operate by pilots. After you raise the thermostat to a higher temperature, it should transmit a signal to the furnace to activate the ignitor.
The ignitor can wear out over time, causing the furnace to not stay lit. It is easy to test the furnace ignitor by following these tips.
Prepare to Work
You'll need a volt meter screwdriver or nut driver, needle-nose, and flashlight for this project. Turn the thermostat to the lowest setting. Go to the breaker box, and find the breaker labeled "furnace, and switch it to "OFF" position.
If you don't know which breaker controls the furnace, shut off the main breaker. Let the furnace cool, if it has been running.
Reset the Ignitor
The ignitor is housed inside the access panel. Use a screwdriver or nut driver to remove the screws on the access panel, then remove the access panel.. Some panels may slide off manually, or they may operate with a handle.
Shine the flashlight inside the box. The ignitor is commonly sitting on a -shaped bracket, and it has a flat metal tip inside ceramic housing with two wires attached.
Inspect the ignitor for chips, cracks, or burns. If it is rusty or damaged, replace it. Otherwise, proceed with the test.
Change the ignitor switch to "OFF", then turn on the main power again after five minutes. Switch the thermostat to "HEAT"; ensuring the furnace door is closed. The fans may operate with an open door, but it won't produce any heat.
Set the thermostat on a higher temperature, and check the vents for heat. Repeat the process several times; increasing temperature. Proceed to do the voltage meter test, if it still fails.
Test with a Voltage Meter
Turn the power off again before you test the furnace with a voltage meter. Use needle-nose pliers to detach the plug on the wires. Set a voltage meter on the lowest setting, Rx1( resistance times one) .
Attach the test probes to the metal contacts on the plug. Restart the furnace, and listen for a click; adjusting the thermostat as needed to turn on the furnace.
You should see 120 volts for several seconds. If you get a 0 or infinity reading, replace the ignitor.
Check for dirty air filters, which could interfere with ignitor operation. If you don't trust your skill to replace the ignitor, or the ignitor doesn't seem to be the problem, contact an HVAC service, such as Custom Comfort.