Furnace won't turn off!

[Michael Press]

I posted a few weeks ago because the a/c in my new (to me) house wouldn't start after I replaced the thermostat. The furnace is covered by a warrentee purchased by the seller so I called them out - the problem was the thermostat (a honeywell 7-day programmable) required that the ground wire be connected to both the thermostat and the furnace. The ground wire wasn't used by the last thermostat and wasn't connected to the furnace. The repair guy dug it out of the wall, connected both ends and then it worked fine. (BTW the honeywell manual never mentioned a ground wire (blue) except for a 2-stage heat pump. This is a conventional gas forced air system). We used the a/c for a couple of weeks until the last week when it cooled down.

So this morning I switched the thermostat back to heat because it's gotten quite cold at night here in the mid-atlantic. The furnace came on. Tonight I noticed the fan was still on so I turned the thermostat to Off, and ... the fan won't turn off! In Heat, Cool and Off modes the fan does not turn off. The thermostat indicates that it's sent a signal for heat or cool when told to and the temps are set right, but when it says Off the furnace still doesn't go off. When I switch from Heat to Off to Cool you can hear the furnace hesitate for a second but then resume blowing. I threw the circuit breaker, which turned off the blower, but then it resumed running when I turned the breaker back on.

Any idea what's going on?

Thanks, MIchael

[m Ransley]

its broke

[CBhVAC:)]

There is NO GROUND wire at all used by a thermostat...none...nada...ever and never.. There is a C, or a COMMON, and thats common to the system, not a ground...

Could have been a black wire...I use black, as the code in our area states...the blue is used for a trouble light...normally called a system monitor..

Yup. But you dont give near enough information to go on, but yet..you do... First, you state the blower hesitates...and that it really does not...its simply going from low to high speed. I would be willing to bet that in the case of an older furnace, you have a bad high limit/fan switch...about $100 depending on the model, if its a higher end Honeywell delay unit, its going to be about $200 or more, again, depending on the model needed...

Or...your "tech" that called a common, a ground, meaning he didnt have a damn clue, mis-wired the unit, and fried a fan control relay, and its now stuck shut. Or, as luck would have it, the relay simply said....no more and is stuck..

[I-zheet M'drurz]

(so many potential mistakes, so little time to read them again)

DAMB! You can see all of THAT? From THERE?? You fukkirs LIED to ME!!!

And here, I was just getting ready to tell him to get a competent tech out there to look at it, and then blow me.

[hvacrmedic]

Since you didn't mention it, you might have set the fan to continuous operation at the t-stat when you switched modes. Check that out and get back to us. Look for the button or switch that says "FAN".

hvacrmedic

[Oscar_Lives]

How do you get a qualified tech to blow you? Do you have a special warranty or something?

[I-zheet M'drurz]

Dayumb straight. I paid extry for that!

[TURTLE]

This is Turtle.

Like CB and hvacrmedic has said. You locked in fan mode by some thing hung up or wired wrong or burnt something to make it hang up.

The tech that was out did not check both heat and cool for operation before he left ?

TURTLE

[CBhVAC:)]

Sure..since we have ran about 40 of those so far this season..:)

Besides...if Dave (cough) can see all he can I think obvious things should be brought up...:)

LOL...I thought about it, but figured..what the hell....

[Stormin Mormon]

And slide that switch to "AUTO".

[Peter D. Tillman]

If the obvious (fan accidentally set to "continuously on") wasn't it, you probably have a bad limit switch -- this is the thermostatic switch that turns off the blower after the heat-exchanger has cooled down. Prob not a DIY job, unless you can dig up a service manual for your furnace.

Good luck!

Cheers -- Pete Tillman

[~KJPRO~]

Or better yet, beings no information to age of the furnace, make and model numbers.............

It could very well be something other then the limit control.

~kjpro~

[Peter D. Tillman]

yeahbut... they still have a temperature-sensor, which can die & give the same effect. I'm guessing anyway .

Cheers -- Pete Tillman, subtly recommending that OP call a good furnace repair guy.

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[HvacTech2]

Hi Peter, hope you are having a nice day

On 12-Jun-04 At About 01:48:48, Peter D. Tillman wrote to All Subject: Re: Furnace won't turn off!

PDT> From: "Peter D. Tillman"

PDT> PDT> If the obvious (fan accidentally set to "continuously on") wasn't it, PDT> you probably have a bad limit switch -- this is the thermostatic PDT> switch that turns off the blower after the heat-exchanger PDT> has cooled down. Prob not a DIY job, unless you can dig up a service PDT> manual for your furnace.

You can't really say this without knowing what model and serial his furnace is. newer furnaces don't have that type of setup. they use a pc board to run the fan.

-=> HvacTech2