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Problem: Furnace Air Conditioner Heat Pump Works Intermittently.


Problem: We have had this question asked many times. My furnace, air conditioner, heat pump works intermittently? Why does my furnace, air conditioner, or heat pump work sometimes, and then sometimes it will not work at all? If I flip the switch on the furnace several times or turn the breaker off and on the furnace, air conditioner, or heat pump will work a few times then it is back to the same problem of not wanting to start and come on? What could cause this problem to happen? Sometimes it works and sometimes it does not work? 

Answer: Thanks for asking this question. We have many people who have this problem with the intermittent furnace, air conditioner, heat pump, and air handler operation and I can say that most of the time I have found the problem to be either loose, burnt wire connections, or internal relays in control boards (need a new control board) that are pitted and worn out. Sometimes the relays, contactor, sequencer will make contact (complete the circuit), and sometimes it arcs and will not complete the circuit.  Below we have a picture of a relay that came off a control board with the black box cover removed. This picture is courtesy of AC Service Tech.  If your furnace starts sometimes and then will not start sometimes then it could be caused by a bad relay on the control board. You will probably need a new control board to fix the problem. If your furnace’s draft inducer, blower motor, or ignitor will not start then this could be a bad or worn-out draft inducer relay, blower motor fan relay, or ignitor relay on the control board. Always check with a volt-meter to make sure that the control board is getting power between L1 and neutral. Make sure all wire connections are tight.  Also, make sure that all your safety controls are closed with the draft inducer running. Safety controls would be the limit, all rollout switches, and the pressure switch. Always make sure that if your thermostat uses batteries that the batteries are in good condition.  Below we have an excellent video that explains Intermittent Faults on HVAC Units that include furnaces, air conditioners, heat pumps, and air handlers. Thanks so very much to AC Service Tech for making this excellent video.  I hope this helps you out. If you have any questions please comment below or email us anytime at

If you would like for us to look up parts then please send your furnace or air conditioner’s model number to and we will be glad to help you find and look up parts. We Would Love to Try and Help You Out and Help You Solve Your HVAC Problem! 

control board relay defective
control board relay defective

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