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My furnace will short cycle on 'AUTO' but when the fan is set to 'ON' it's fine

My furnace will short cycle on 'AUTO' but when the fan is set to 'ON' it's fine


Old 12-18-16, 12:53 PM
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My furnace will short cycle on 'AUTO' but when the fan is set to 'ON' it's fine

Any idea what this could be? Basically if i put the fan on auto, the furnace will occasionally short cycle before it decides to work correctly. When it short cycles (random as far as i can tell) the burners turn on, then the blower turns on, then the burners turn off and then the blower turns off a bit after that. It'll eventually always get the house to the temp i set it at but is annoying and probably inefficient and bad for the system. If i put the blowers to 'on' instead of 'auto', it'll never short cycle--it works perfectly fine. Thanks guys!
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Old 12-20-16, 06:48 PM
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Do you have a digital thermostat? If not, the heat anticipator may need to be adjusted. You would be ahead of the game to install a digital.
Old 12-20-16, 10:19 PM
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amatuer plumber has a whole load of threads on the trials and tribulations of his nest installation.

You would need to determine what turns the blower on in the heat mode. It could be a thermal switch or time delay.

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