My furnace has recently started acting a bit oddly. It heats to the set temperature and switches off. But a minute or so later, it comes back on for just a few seconds, then immediately back off. I change the furnace filter regularly, but I changed it early to make sure it wasn't that. It was barely a light gray, but I put a new one in anyway and that didn't help. I did put a new thermostat in about 4 years ago (it's a Hunter 44260 if that helps) could that have gone bad already? I tried pushing the reset button on it to see if that would help, but again no luck. Anyone know what it could be?
The indoor blower is controlled by temperature in the heat exchanger. When the flame turns off there is still heat in the heat exchanger that needs to be put into the home before the fan turns off. After all, you already burned the fuel, you might as well get that heat into the home rather than wasting it. The indoor blower continues to run and the heat exchanger cools down as that heat is removed. When the temperature has lowered enough the blower stops. Sometimes there will still be enough heat in the heat exchanger area for that switch to remake and turn the blower back on. This has nothing to do with the thermostat, it is a control device inside the furnace itself. It is possible the switch is wearing out and needs to be replaced. You should have a qualified service technician come in and check this out. The technician will know where to find a replacement switch if its needed and should be able to tell you exactly how much it will cost and how long it will take. He may well have a replacement switch in stock on his truck. This is not an uncommon problem. Total time to diagnose and repair should be about one hour at most. There are other things that could be contributing to this. A restricted air flow from a dirty air filter or from a bad blower motor could reduce the ability of the heat exchanger to give up its heat. The technician will be able to give you a more accurate answer to what is going on once he has the opportunity to check it out.
If it finishes the cycle and just the FAN comes on briefly then it is trying to cool off. If the filter is clean and all the registers are open then it could be that it had a long heat cycle and is trying to finish cooling off
Furnaces have a temperature switch that shuts down the blower after the furnace fire goes out. It's function is to see that the furnace heat exchanger is cooled down before the circulating fan shuts off. It sounds like this switch is not working properly.
most thermostats have a 4 degree differential, try setting it to a different temp and see if it cycles properly. take the cover off the thermostat and clean out any dust.
What you have happening is a simple problem, and nothing to be alarmed about. There is a combination fan/limit switch in the furnace thats job is to sense when the heat exchanger is warm enough to turn the blower on and cool enough to turn the blower off, the deal is that maybe it is shutting off a little too early and while the blower is off there is just enough heat in there to turn the fan switch enough to bring the blower back on momentarily, that switch most likely is needing replaced and I would refer that to a hvac company. but like i said its not going to hurt anything just annoying thats all.
