furnace fan doesn't shut off. heat kicks on off. Is thermo bad?

[coffeeman]

Hi all
Heat works, but fan doesn't shut off when unit not calling for heat. Temperature is fine, but heat blower doesn't shut off. Removing thermostat from base will shut down fan. Of course, shutting fan switch on air handler off works too.

I'm guessing thermostat might be cause. Is there anything else that could cause problem? The thermostat replacement is $75.00 for exact part number from Honeywell.

Should I get thermo or call a heating person.

Cheers.....Coffeeman

 

[zzvyb6]

I had this happen (TWICE). First was a burned/inop internal temperature sensor failure (Not the thermostat). Replaced and ok for a few weeks. Second time was same thing: Burned temp sensor. I ordered a new furnace. Heating company noticed I was using the new type very high efficiency air filters. He was measuring 'make-up' air flow and stated that my old furnace was starved for air and had overheated. For the new furnace, they swapped out some heat duct runners to get more cold air return flow.

If your furnace is a very high efficiency deal, check the inlet and outlet piping to see if ice or critter) buildup has blocked off either or both pipes.

 

[CobyRupert]

Coffeeman,
I assume you have hot air furnace system and the "heat blower" fan you're talking about is the fan that circulates the air from your house, through the furnace and back into the house through registers?

I believe this fan is usually triggered by a thermostat (temperature switch) on the furnace's fire box, that's why air circulation doesn't start immediately when furnace comes on until firebox comes up to temp; and it will stay on for a while after furnace fire has turned off until it has cooled.
However your interior wall mounted thermostat (the one your wife turns up) may have a "blower only" or "fan on" setting that bypasses the "auto" setting described above. Is this the thermostat you mean when you say "Removing thermostat from base will shut down fan."? If so, check settings, but it seems like the contacts on this thermostat that bypass the furnace's temperature switch have welded closed and won't open.

 

[RNeumann]

A typical furnace only needs to have the red and white wire connected to make heat. If unplugging the thermostat turns the fan off the problem is likely the thermostat. I wouldn’t spend $75 to figure that out though. I know enough to know how thermostats are wired so I’d just connect the red and white wires together and bypass the thermostat. If that scares you you can buy a cheap thermostat to verify it’s thermostat- probably cost $10 or so.

If you sent a photo of the thermostat with model and another of the thermostat wiring- this is typically exposed when the cover is removed from the thermostat. With those two photos us TBNers could get you pointed in the right direction. Most thermostats are wired the same- the photos will just verify that.

 

[coffeeman]

Thank You for comment
My heat is distributed to rooms through an air handler, both hot and cold. I have a hot water boiler and an air-conditioner. Winter hot water runs to air handler. Summer air conditioner runs cold to second exchanger.. Very similar to heat pump using a backwards heat exchanger, except my heat comes from gas boiler.

little complicated, but I'll get back to you. I'm still at work now so it will be till tomorrow. I think you might be saying get the red and whitened could actually connect a simple on and off switch to it also. Less expensive is jumper wire.. I am speculating here as I am not a furnace guy. I have an electronic thermostat.

Thanks for the good ideas and info.......Coffeeman

 

[coffeeman]

Thank You for comment
My heat is distributed to rooms through an air handler, both hot and cold. I have a hot water boiler and an air-conditioner. Winter hot water runs to air handler. Summer air conditioner runs cold to second exchanger.. Very similar to heat pump using a backwards heat exchanger, except my heat comes from gas boiler.

little complicated, but I'll get back to you. I'm still at work now so it will be till tomorrow. I think you might be saying get the red and whitened could actually connect a simple on and off switch to it also. Less expensive is jumper wire.. I am speculating here as I am not a furnace guy. I have an electronic thermostat.

Thanks for the good ideas and info.......Coffeeman

I FIXED IT..... Thanks all for offering help. Fan ran for two weeks. I had working heat. Why fiddle with heat? I decided thermostat might be malfunctioning. Priced them. Posted here for suggestions. Usually I get good info from TBNers. While posting above post a lite went off in my head. Humm??
Fan?? Fan?? Humm?? Isn't there a fan setting on thermo? WOW! I was so sure of fixing. Drove home.. Called wife over and said, "I'm gonna fix the heat fan." Went to thermo.
Changed fan button from "FAN" to "AUTO" Now, that's an easy fix....

Thanks all for any and all input for help today and over the years. TBNers are always helpful. It's a pleasure to visit here. I wish I had time to visit more often.

Cheers......Coffeeman

 

[RNeumann]

Glory hallelujah!

 

[Tractor Seabee]

I run my fan all the time. The small fractional HP motor doesn't use enough power to show on the bill. Maintains a more even heat in the house and keeps the electronic air cleaner working on the air all the time.

Ron

 

[RNeumann]

I run my fan all the time. The small fractional HP motor doesn't use enough power to show on the bill. Maintains a more even heat in the house and keeps the electronic air cleaner working on the air all the time.

Ron

I’ve heard of folks with wood stoves doing this. Some of the newer thermostats have a “circ” feature that runs the fan randomly 1/3 of every hour.

 

[goeduck]

I run my fan all the time. The small fractional HP motor doesn't use enough power to show on the bill. Maintains a more even heat in the house and keeps the electronic air cleaner working on the air all the time.

Ron

I tried that but it felt drafty. I have thought about adding a repeat cycling relay to get some circulation but maybe the circ Tstat that RNeumann mentions is the ticket.