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Problem: Furnace comes on, doesn’t run long then shuts off. Will work if thermostat is turned way up.

Problem: Furnace comes on, doesn’t run long then shuts off.  The furnace will work if thermostat is turned way up.

Answer: This sounds like a thermostat problem or an over-heating problem. I would suggest taping the furnace door safety switch closed so it allows the furnace to stay on so you can test the controls. Test with a volt meter set to volts AC and see if you are getting 24 to 28 volts between the W and C (com) terminals on the control board from the thermostat when the furnace shuts off. If you see that 24 volts goes to zero between W and C when the furnace shuts off then the thermostat is cutting the furnace off and you have a thermostat problem. If you continue to get 24 to 28 volts between W & C then you have another control shutting the furnace off. This could be a safety control like a limit, rollout switch or pressure switch cutting the furnace off. Test the limit with you volt meter. If the limit is going to zero (open) then you would have a furnace over-heating problem which could be caused by a slow blower motor, (please check the capacitor) could be a stopped up filter, AC evaporator coil or the gas valve maybe outputting too much gas into the furnace. Please click here if you are interested in seeing the furnace limit and rollout switches we sell. Below we have a YouTube video that was made by Grayfurnaceman which shows how to troubleshoot a furnace limit. I hope this video will help you out. Thanks to Grayfurnace man! Thanks so much for your interest in our website! If you have any questions please feel free to email us at: support@arnoldservice.com or respond in the comments section near the bottom of this page. We hope you have a blessed day! Steve & Barbara Arnold

4 thoughts on “Problem: Furnace comes on, doesn’t run long then shuts off. Will work if thermostat is turned way up.

  1. I have a goodman furnace flame goes out just before the fan kicks in fan stays running true the rest of the attempt it will light but go out

    1. Hi Paul! I would suggest that you check your safety controls like the pressure switch, limit and rollouts to make sure they are staying closed when the gas goes out. You will need a voltmeter to do the testing. I would suggest testing to make sure you are getting a constant 24 to 28 volts AC between the C and W terminals on your control board. If the voltage is dropping out during a heating cycle then you probably have a thermostat problem. If your thermostat has batteries please make sure the batteries are good. I would like to suggest that you check all wire connections and ground wires to make sure they are all good and tight. We have lots of furnace troubleshooting advice on the following page: https://arnoldservice.com/gas-electric-furnace-troubleshooting-simplified-2/ I would suggest going through the troubleshooting flow chart to see what is wrong: https://arnoldservice.com/wp-content/uploads/2014/12/furnace-troubleshooting-flow-chart.pdf We also have lots of troubleshooting questions and answers on the following page: https://arnoldservice.com/furnace-troubleshooting-questions-answers-index/ If you have any specific questions please let me know. Thanks! I hope you can easily find and fix the problem.

  2. I have a lennox furnace modelnumber G12Q3-137 it keeps coming on and shutting off every 5 seconds i changed the thermostat, thermocoupling and the transformer thats what i was told it was but it still is doing it what else could it be thank you

    1. I am not familiar with Lennox furnaces but if you have a spark ignition furnace it could be the control board that is the problem. I have had seen this problem with other spark ignition furnaces. Sorry, I do not have a Lennox parts program where I can look up parts. It sounds like you are definitely having a flame sensing problem since the furnace is cutting off within 5 seconds. I would suggest making sure all wire connections are good and tight especially the ground wires. Make sure that the burners are good and clean and burning a blue flame. If your furnace has a pressure switch make sure the pressure switch is staying closed the whole time the draft inducer is on. If your control board has a flash code try and read the code to see what it is showing is wrong with the furnace. We have lots of furnace troubleshooting advice on the following page: https://arnoldservice.com/gas-electric-furnace-troubleshooting-simplified-2/ I would suggest going through the troubleshooting flow chart to see what is wrong: https://arnoldservice.com/wp-content/uploads/2014/12/furnace-troubleshooting-flow-chart.pdf We also have lots of troubleshooting questions and answers on the following page: https://arnoldservice.com/furnace-troubleshooting-questions-answers-index/ If you have any specific questions please let me know. Thanks! I hope you can easily find and fix the problem.

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