My gas furnace is blowing cold air some of the time. The burner kicks in for about 10 seconds...
then kicks off, then the fan starts.(blowing cold air). Some times it works properly, heating longer and keeping the temperature up. Other times the temperature can drop down lower than the setting, then finally it realizes it's too cold and then works again. Any ideas? thx
There could be a couple of reasons for this, the most likely is faulty thermostat. If the thermostat is going bad it may work intermittently. Another thing to check is furnace ignitor, it may be coming on like it should and trying to blow hot air but the ignitor is not actually firing the furnace. The gas control valve could also be a problem. the unit could be firing and then shutting off too soon because the gas isn't flowing properly. Many reasons for similar problems but without more information on the unit make, model, and age its hard to pinpoint one cause.
I know this is late for an answer, 9 times out of 10 the safety sensor will have build up on it. it is near the heat source and looks like a disc with two wires trailing from the end. All that is needed is to remove from the sidewall, clean with a alcohol based cleaner and replace. If you do not have a good knowledge of gas equipment then I would suggest you stop, and think about the risk before going into your unit. Always turn the GAS off before you open the unit. Safety first. Good luck!
There are several possible causes for a furnace blowing cold air, so it’s hard to give you advice without more information.
But here are 3 common causes you can fix yourself.
1) Thermostat is set to ON
Is your furnace blowing cold air only sometimes? Is the furnace’s blower constantly running?
2) Furnace overheated
Let’s say your furnace blows hot air, then cold air, but then stops blowing any air at all after a while. What’s the problem?
3) Pilot light is out
If your gas furnace is only blowing cold air, then the pilot light may be out. Check to see if it is and try these solutions:
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