Furnace fan won't shut off

[rrunner]

Have a 7 year old oil furnace and last month the fan came on and won't shut off
any ideas out there I have no knowledge of a furnace. Heating with wood this winter so I still have heat. I have also tried shutting off the fan button on the furnace, NO GO.


Thanks to everyone who replied will check out the suggestions, some I did not think about..

[torpainter]

what kind of thermosat control do you have?

[StanW]

An oil furnace should have a 2 position fan switch - on position and auto ( receives a signal from the thermostat/furnace/heat sensor) . I would check that first.

[Terryl]

Sounds like a stuck relay on the controller board, you need to get a furnace guy to look at it in my opinion.

This happen to my sister, her heater came on when she was out of town, I went over to check on things and almost burnt my hand on the door knob, the walls were so hot by the furnace you couldn't touch them, all the wax candles had melted.

Furnace's should be looked at at (and cleaned) least once a year by a pro.

[StanW]

... sounds like just the fan is running :noidea:

[rrunner]

It is an old honeywell.

[rrunner]

yes just the fan is running not the heat.

[StanW]

... so is just about every 2nd thermostat on older oil furnaces .lol

[rrunner]

I have 2 settings on the thermostat and also 2 position on the furnace tried both and still won't shut off. I shut off the main switch(like a light switch) and it shut the fan off.

[StanW]

There is a thermal switch somewhere on the furnace ( it will keep the fan on when a certain temperature is surpassed) - if it is burned it will force the fan to stay on . It is easy to verify with an ohm meter .

[rrunner]

Wow great information from everyone. thanks

[Terryl]

I would try a new thermostat also.

[Pollypurabred]

Did the fan restart when you reapplied the power?


I have 2 settings on the thermostat and also 2 position on the furnace tried both and still won't shut off. I shut off the main switch(like a light switch) and it shut the fan off.

[StanW]

Apparently - read post 9.

[rockin62]

Check thermocouple if you have a pilot light. If the pilot is on the thermocouple is good. Check fan relay switch aka hi/low relay. This relay controls on/off for fan when the thermostat calls for heat. These two options are the cheapest to check and not to take away form the other suggestions from the other fine members who have responded to your issue.

Good Luck and I hope it isn't too expensive as one could buy a new receiver to test for the money it takes to have a repairman come in.

[StanW]

... a pilot light ? :noidea:

[lars]

I think you can pretty much outrule the thermostat being faulty because if it were it would also be calling for heat. As stated earlier, try to determine why the fan relay wont drop out. possibly stuck? overtemp sensor gone bad? just be careful where you stick your fingers.:yes:

[rrunner]

yes fan restarted and kept going, have a friend (electrician) coming this week to look at it, tried all I could with all the help everyone gave but looks like we may have to get someone who knows a little more than I do. again thanks for all the great suggestions.

[oldskool]

There are settings for the fan motor to shut off/on on the thermostat. These are limiting for hi/lo temperature that controls the fan. Sometimes there is an auto/manual switch also for the fan to run continuously. Manual position is good in the summer, if you want to cool the house because the fan can be left on at all times.

[peanut 1]

i agree with oldshool i would see if someone hit the summer fan switch by mistake

[rrunner]

Thanks but checked the switch on both ends.... will keep plugging away until the electrician gets here....

[MeSat_FTA]

If you have a voltmeter, then you need to do some testing.

1. Does your fan use a relay? If it does have a relay, is the relay being energized? Unplug one of the the coil (input) wires and see if the fan still runs.

2. If the fan still runs, then the relay is contacts are welded shut. Very common problem. If the fan doesn't, run then the problem is the relay drive. Where does that come from?

3. Some furnaces use a thermal couple probe to test the temperature is hot enough to turn the fan on. If this is your furnace, then you have to measure the voltage from the probe and the input to the circuit. It may be broken or shorted. The driver circuit could be shot as well.

Without details, then it is hard to find and suggest a fix.

My furnace has a DC motor that runs at two speeds. Slow speed all the time and fast speed when the heat is on. This filters and circulates the air.

[DSD]

Seen that nobody has asked if you have a interlock switch .Its a switch that when turned on it turns a bathroom fan and your furnace fan on at the same time .They became code in Canada about 10 years ago .My daughters house has one and the switch failed ,so when it would call for heat and heat up the house the furnace fan would not shut off after the burner stopped .The switch is usually by the thermostat.Also you might look on the circuit board to see where its hooked up if its so equipped and disconnect it.

[Pollypurabred]

Since fan restarted when reappling power it is probably the thermostat or a faulty relay. Suggest turning power off again, removing the three or four wores from the thermostat and then reapply power. If fan starts it is at the furnace end (faulty relay + bad clicks-on (thermal) switch.

[nice_prguy]

It is not no thermostat, or not a thermocouple either. It is either the manuel fan control switch has been accidentally turned to the on position. The fan control is usually located in behind the front door of the furnace, it is a grey box, and it has a little switch or button that says auto/man just turn it to the auto selection... If it is not this then it could be that the temp setting inside this little box, for the fan on/off for the off selection is set to low... Or it could be that the furnace kicked off on high limit and needs to be serviced... these are the only things that could create this problem.... good luck... The Furnace Guy

[cranky]

Most oil furnaces have a combo fan high limit switch.Sounds to me that is your problem. Switch has a dial with temp range from 50 degrees to 250 degrees. it has 3 pins on it the first one set at lowest temperature is your fan shut off setting, the 2nd is for your fan to come on and the 3rd is to shut off your burner in case your fan doesn't work. It will be a honeywell control and may have a push button (fan on and fan auto button on it.) You push the button in to have your fan run all the time. check this first. If not rotate the button to the lowest setting slowly to see if fan shuts off. Be careful the 3 wires you can see that are attached to this control are live with line voltage.....

[aquadave]

It's the fan relay. oil/gas burners lots of time have 2 relays 1 for normal operation and 1 to control the fan after it heats up and won't shut down til it cools off. they look like little black boxes 1 1/2"x1" with 4to8 1/4" spade terminals replace them both they're cheap

[love2hack]

The limit switch is likely set low, or stuck on. Check the settings on low limit!

[Pollypurabred]

This is an old thread but I was hoping that rrunner (http://www.satfix.net/member.php?45965-rrunner) would get back to us, but nay.

[hutch]

prollly someting dum like I had. HVAC guy wasn't paying attn. switched wires on thermostat when reconnecting. Fan stayed on until I took thermostat apart & voila correct color wire to correct position & it works fine.