High Efficiency Furnace Problems And Reviews

Question: Why does may high efficiency furnace fan turn on then back off?

(Posted by: jalash123 on 2009-01-09 04:35:42)

I have a high efficiency furnace and it will go through a heating cycle and then turn off. After a minute or two the fan will turn on for about 30 seconds and shut off, and then sometimes do this again. Is this something that should be look at?

Posted by: gizmoe on 2009-01-09, 05:00:49

Most high efficiency furnaces use an electronic timer for the blower sequence and would not do that normally. Could be you have an older high efficiency furnace that has the older fan control and could come back on if the heat is building up. Maybe just needs adjustment. Another possible cause may be a digital thermostat. Some digital thermostats without batteries steal power from the furnace through the control wire and can cause intermittent heating or blower operation. A resister can be added to correct this.

Posted by: moe49 on 2009-01-09, 04:42:18

Just had mine checked this week for this very reason-it is a cool down for the furnace-a way if you will to dump the built up warm air that is inside ; i tried to explain in a summarized version of what i was told during my inspection;hope that i helped you

Posted by: DAN THE AC MAN on 2009-01-09, 05:16:38

Problem is more common on older furnaces that had temperature based fan controls..if fan control didnt run fan long enough after tstat shut off the burner then the heat would build back up [ with burner still off] and trip the fan control on briefly.....this is unusual in a modern hi-eff furnace since the fan on/ off is usually timed,,not temperature based....if your furnace is a downflow [ counterflow] that has a seconday limit in the blower compartment,,maybe the fan control isnt running the fan long enough after burner shuts off,heat building back up enough to trip secondary limit,which causes the fan to come back on.. ...or whatever type furnace you have isnt running fan long enough at the end of the cycle,causing some type of limit to open,or some type of fan control to turn on fan briefly...i dont think is normal operation for any furnace,even though a lot of the older ones do it,,it is correctable by adjusting/ replacing the fan control....it is a rare condition in newer hi-eff furnaces,,,get it checked ,,the extra heat that might be there due to fan not running long enough could damage the plastic ac a-coil drain pan if you have one,,also hard on the furnace heat exchanger...........dan

Posted by: david d on 2009-01-09, 05:29:22

As it is "high efficiency ", it probably has a thermostat that automatically turns it on and off. It reaches a certain temperature and turns off. The surrounding air cools off to a certain temperature and it turns on again. It wouldn't be efficient for it to be on constantly. If it did run all the time it would heat the room until you were too hot and you'd have to get up and turn it off. Then the room would start getting cold and you'd have to get up and turn it back on to heat up the room! So, it turns off sometimes and then turns on again.

Posted by: Richard M on 2009-01-09, 18:30:33

If your furnace has a plastic vent pipe: Replace your air filter first. If the problem continues, the fan/ control circuit board is defective. If your furnace has a metal vent pipe: The Fan/ Limit control is defective.