Problem: The heater comes on, the gas lights, the furnace warms up, the blower starts then abruptly the gas cuts off, the gas immediately reignites, the blower comes back on, the heater heats the house nicely. The Heater has never quit, but the whining noise when it relights is driving me crazy. I’ve replaced the ignitor and flame sensor with parts from Arnold in the last two weeks. The flame sensor helped in that the heater now occasionally runs normally, with no second lighting of the gas. I’m very handy and have a professional Volt-Amp meter. I’m stumped.
Answer and Possible Solution: Thanks so much for your business and interest in our website! This sounds like you have a furnace short cycling problem. We have a really good YouTube video below that shows why gas furnaces short cycle. We have this question asked many times and the question is “Why does my furnace keep shutting off before the desired temperature on the thermostat is reached?” My suggestions would be to test the limit, pressure switch, and rollout switches to make sure they are staying closed when the burners kick out. If one of these safety controls opens then this would cause the erratic operation of the gas going off and on. If these safety controls all check out OK, then I would suggest taping your furnace door safety switch shut to make sure that the furnace’s power stays on and make sure you are getting a constant 24 to 28 volts between the W and C (com) wires on the furnace’s control board coming from the thermostat. If the 24 volts voltage drops out between the W and C (com) terminals when the gas shuts off then you have a thermostat or a thermostat wiring problem (possible short in wires or loose wire connection). Always make sure the thermostat batteries are in good condition if your thermostat has batteries. With the furnace door safety switch taped to stay ON then try to read the furnace control board’s flash code. On most furnace’s the furnace control board will flash a code that tells you what the problem is with the furnace. The key to the flash code is usually glued to the furnace’s blower door. If you are getting a whining noise in the burners when the gas burners are burning then I would look at the gas orifices and burners to make sure they are not dirty or partially stopped up. This could also be caused by too much or too little gas pressure. Most of the time it is too much gas pressure. This could also be the problem of the gas shutting off if the flame sensor is not engulfed in a nice blue flame when the burners immediately ignite. If there is too much gas pressure, especially when the furnace is cold the burners will not light properly and the flame sensor might not sense the flame right and cut the burners off. You might need a new furnace flame sensor. Please click here if you are interested in seeing the furnace flame sensors we sell. Please send me your furnace’s model number if you would like for me to find out which flame sensor part number or part your furnace uses. Our email address is firstname.lastname@example.org Best of luck in finding the problem. I hope you have a blessed day. Thank you so very much for your business! Steve Arnold, https://arnoldservice.com