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Old 10-03-2010, 11:35 AM   #1
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Furnace won't fire, exhaust fan hot and won't start


Guys
I have a intercity NUGK100DH11 furnace built in 92. it has a Fasco exhaust fan 7062-4578. Just bought the home had a AC checkup a few months ago and now trying to get heat I find the furnace won't fire up. The exhaust fan gets real hot (too hot to touch) and will not start which I think is the problem. Is that a bad fan or could something else be stopping it from starting (seems it would not overheat if some switch was not letting it start) I did find a small black round disc with two red wires (one going to the fan) unplugged right behind the gas control valve. It covered a small white button under it.
Any suggestions?
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Old 10-03-2010, 11:49 AM   #2
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Furnace won't fire, exhaust fan hot and won't start


Post a pic of that disc thingy. If it is a limit control and somebody bypassed it you could be in danger. Remove the smokepipe from on top of the fan and look inside for a dead bird jamming it. Very common for those fans to seize up from usage/old age at that age. That furnace has problems with heat exchangers cracking/popping compression rivets so you may want to get a Pro to check it for safety.
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Old 10-03-2010, 11:57 AM   #3
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Furnace won't fire, exhaust fan hot and won't start


Sounds like someone bypassed a roll out switch. Which as Yuri said, Is a BAD thing.

post pic as he said.
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Old 10-03-2010, 12:26 PM   #4
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Furnace won't fire, exhaust fan hot and won't start


Here is a photo of the connection that was disconnected. Covers a small white button under it. I will check for a blockage in the line.
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Old 10-03-2010, 12:29 PM   #5
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Furnace won't fire, exhaust fan hot and won't start


Yep. Thats a roll out switch.

Don't be surprised if the heat exchanger is bad on that furnace.
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Old 10-03-2010, 12:34 PM   #6
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Furnace won't fire, exhaust fan hot and won't start


Would a bad heat exchanger stop the exhaust fan from coming on? the fan just makes a small noise and gets hot fast but never turns on.

Would the system have run with the rollout switch disconnected? pressing the white button under the cap does not do anything either.

Is a bad heat exchanger replaceable or are we talking new furnace?

The fan sounds like it has power to it and is trying to turn but does sound as if it seized up. it starts to smell after a bit.

Last edited by tex800; 10-03-2010 at 01:02 PM.
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Old 10-03-2010, 01:28 PM   #7
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Furnace won't fire, exhaust fan hot and won't start


Yes, it would have ran with the roll out bypassed.

The roll out bypassed is not preventing your furnace from running. You need to check what is stopping the inducer/fan from running. As said earlier, it could be a dead bird. Or the motor is done for.
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Old 10-03-2010, 01:29 PM   #8
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Furnace won't fire, exhaust fan hot and won't start


That is a potentially DEADLY situation you have there. If it is bypassed because the flames are rolling out from a cracked heat exchanger you WILL get CO poisoning and die!! Get a Pro to check it PROPERLY.
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Old 10-03-2010, 01:48 PM   #9
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Furnace won't fire, exhaust fan hot and won't start


Thanks guys, have a guy coming out next week. So basically the fan not working is one issue and the rollout switch being bypassed and WHY are definitely another serious issue. With rollout switch now connected back and I get the fan working the system still may not work if rollout switch does its job due to bad exchanger?
Just trying to get my head around it.
thanks
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Old 10-03-2010, 01:53 PM   #10
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Furnace won't fire, exhaust fan hot and won't start


Yep, that furnace is known for bad heat exchangers (just like others) and sometimes the sides of the burners get holes in them from corrosion. Flame then spills out sideways and can rollout the front. Burners are obsolete where I am. Takes 5 mins of running B4 that shows up.
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Old 10-03-2010, 02:01 PM   #11
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Furnace won't fire, exhaust fan hot and won't start


The tech can check the heat exchanger while he is there. Before he replaces the inducer.
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Old 10-08-2010, 08:46 AM   #12
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Furnace won't fire, exhaust fan hot and won't start


The tech came and said the inducer was bad but had to order one. while there he said don't use the system. I asked why not the AC works fine and we use the fan to circulate air. He finally said OK and 10 minutes after he left the breaker blew and the fan will not fire up. as soon as you power up system and call the blower motor it trips breaker. Red lead from main blower motor shown in pic below looks like it blew off circuit board, this is right below or part of the fan relay I believe. Any clues what happened? i guess this is the terminal board, suspect we are not able to just attach to another unused terminal on the board?
also said heat exchanger looked like normal wear and tear but looked ok but still needs to fire up system to tell for sure.

Last edited by tex800; 10-08-2010 at 09:49 AM.
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Old 10-08-2010, 04:56 PM   #13
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Furnace won't fire, exhaust fan hot and won't start


Doesn't sound like you got the best tech.

The inducer being bad should have no effect on the A/C.
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Old 10-08-2010, 06:45 PM   #14
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Furnace won't fire, exhaust fan hot and won't start


If that's "R" then there's a good chance lots of controls are fried. Going to get real expensive real fast. I wouldn't put any money in that 18 year old furnace.
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Old 10-08-2010, 06:48 PM   #15
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Furnace won't fire, exhaust fan hot and won't start


I don't think those are his low voltage post.
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