Possible furnace issue or safety device?

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Old 01-05-18, 12:22 PM
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Possible furnace issue or safety device?

Hello...my furnace just started doing something different... but im not sure if it's supposed to do it or if there is a problem. Normally my digital thermostat says "heat on" , the furnace "clicks" and the furnace starts a short time after. When the house reaches setpoint temp the furnace "clicks", the "heat on" words disappear from thermostat screen and the furnace shuts off shortly after.

My problem is: as of a couple days ago, in between normal furnace operation listed above, my furnace(blower) turns on for a very short cycle(less than a minute) without the normal "click" sound from the furnace and my thermostat does not say "heat on".

Im not even sure this is a problem? Maybe a safety feature of some sort? The furnace is working/ sounding fine except for this rogue run time between normal cycles.
Thanks!
 
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Old 01-05-18, 12:32 PM
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Welcome to the forums.

Does the blower come on by itself close to when it's finished a heating cycle ?

Sometimes the plenum remains hot after a heating cycle and is cause for the fan to come on momentarily. If it just pops on randomly during the day.... that could be signs of a problem. A make and full model number would be needed to check further. The model number can be found on an ID tag on the inside wall near the burner.
 
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Old 01-05-18, 12:37 PM
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Doesn't sound like safety issues. Has the stat been changed out ?
 
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Old 01-05-18, 05:33 PM
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Given the time of year... If you have a "smart" thermostat, it's possible that it is commanding the blower to run so your humidifier can work once in a while. You would have had to enable this, and you can disable it.

Do the burners fire up when it does this random thing? If so, ignore everything I just said.
 
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Old 11-17-18, 12:20 AM
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Im experiencing this too, it started last july. I live in a semi arid/ sometimes humid always hot climate. I noticed after a rain the blower started without call to cool, followed by furnace exhaust fan spin up. The exhaust fan cycles off and on a few times for several minutes then all is quiet. These bouts come up a few times a year and usually after high humidity. Im not sure what limit switches could set this pattern off, but i will eventually get a round tuit. It is not the thermostat.
 
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Old 11-30-18, 02:13 PM
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https://www.doityourself.com/forum/gas-oil-home-heating-furnaces/374364-goodman-draft-inducer-fan-keeps-cycling-off.html nails the symptoms, but never any proposed solution. Its not thermostat related because call for fan wont start exhaust fan. Call for heat would start ignition cycle. And disconnected tstat shos the problem is in the furnace. Seems increase of heat and humidity starts it off. Is the fan limit switch going to start exhaust and blower fans? And allow exhaust fan to cycle ? (Dont suggest it's short cycling please.)
 
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Old 12-01-18, 12:50 AM
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It is not the thermostat.
Have you removed the thermostat and the problem remains ?
If you know it..... post the model number of the thermostat.

An open safety or limit switch at any time can cause the blower to run but ONLY the thermostat can call for heat to turn on the draft inducer.
 
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Old 12-03-18, 01:54 PM
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Sorry i wasnt more clear. I have observed this while thermostat and leads are disconnected from the furnace. And this is not a call for heat. Only the fan blower and exhaust fan are going. No ignition sequence.
 
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Old 12-07-18, 04:27 PM
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Seems to be happening more frequently. Consistantly when the ambient temp and humidity rise. When the air cools and drys the problem stops. Call for heat is unimpeded, and low humidity after a couple of calls for heat seem to stop the problem too. I recently recalled that it first happened after a condensate overflow last July.
 
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Old 12-07-18, 07:44 PM
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Only the fan blower and exhaust fan are going
If you have the thermostat disconnected and the draft inducer is running..... my first thought is the control board is bad. Like I mentioned.... ONLY the thermostat can call for heat causing the draft inducer to start.

However my previous answer is not 100% correct.... with some furnaces when a safety limit trips it can cause the draft inducer and blower to run.

This problem should cause a fault to set on the control board.
Post the model number for the control board.
 
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Old 12-11-18, 12:49 AM
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Im not 100% but i think it is B1809913S. I dont knw where on the board it is printed.
 
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