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furnace cycling on and off

Hello, I have a question if anyone can help me out. My thermostat is set at 68 and the temp. is 64. My igniter or glow plug gets hot and the furnace fires up. Then about 5 seconds later i see the plug cooling down and the gas shut down. I did the gas shut down on the back of the panel waited the 5 minutes etc. Thank You

Re: furnace cycling on and off

Either the flame is not going all the way across the unit or the flame sensor is bad. . Some times just cleaning the tip with some fine steel wool will cure the problem.

Re: furnace cycling on and off

Many things can cause the firing to shut down.....

Thermal coupler
negative pressure switch and/or hose
blocked intake
blocked exhaust
poor electrical connections internally
poor ground connection
faulty module
faulty blower motor
faulty temp sensor

so on ....

Re: furnace cycling on and off

To add to the above posts, many times I find if you follow the igniter/probe wire back to the gas valve of control module, the connection is suspect, I've had to tie wrap them in a certain direction to get a good connection until I was able to replace the valve or module.


Re: furnace cycling on and off

If the furnace fires up and shuts down 5 seconds later it is more than likely the flame sensor, they are designed to shut the unit down after that amount of time if it doesn't see the flame, as JLM said. Good Luck!!!:)

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