TEMPSTAR SP80 No hot air after 30 minutes

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Old 03-20-08, 10:36 PM
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TEMPSTAR SP80 No hot air after 30 minutes

I have a TEMPSTAR SP80 furnace. After the furnace is running about a half hour and the hot air become cold air. The inducer fan and main blower are still running. There is no fire from burners. The igniter is on and only little frame in middle of burner.

Can anyone help?

Thanks,
 
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Old 03-21-08, 05:18 PM
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Sounds like it limited and you may have to shut off the furnace and let it sit maybe 15 seconds, then turn it back on to reset it. The inducer keeps running because it is still calling for heat. The main blower fan keeps running likely because either it is controlled by heat and it is told to come on to cool the hot heat exchanger down, or it is on a fan timer and it is running simply because of the call for heat still.

There could be other problems from what I stated, but this seems the most likely since it ran for 30 minutes straight. I have also ran into flame roll out switches that have gotten too hot from the limit switch being set to 250, rather than at 180, and all that heat trapped beneath the furnace front panel cover is to hot for the rollout switch, or maybe the rollout switch is on the cusp of going and that additional heat is the last straw.

Do you know how to check all the ~24 AC volt safety switches inside the furnace?, like limit switch?, and pressure switch? and roll out switch(s)?, and spill switch (if you have one of those). If any of those is open when the furnace is running the flame shuts off.

Why is your furnace running so long in one duration? Is it really really cold where you are?, and you had the furnace set back to 55-60, and then you turn it up to warm the house back up?
 
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Old 03-22-08, 09:27 AM
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Thanks ecman51,

It runs 20-40 minutes every time after I shut down and restarted.

It seems like the little frame is the problem that keeping inducer and main blower running.

I wish I can post a picture.

I know some of these switches, but not all of them.

I am in the Midwest and it is Spring now. It is not really cold for now. It runs continually over a hour in extreme cold weather.

Thanks again.
 
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Old 03-22-08, 12:34 PM
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You have mentioned "frame" in 2 posts. Frame? Or flame? The "r" and "l" are nowheres near each other on the keyboard, otherwise I'd presume you mean flame.

I can't get over how long the furnace runs for. (Up to 60 minutes straight when cold out?. And with the thermostat left on it's normal setting?)

When it runs as long as you say, is that with the flame still going, or have you just presumed it stays going up until the air feels cool? If your house does not leak out heat as fast as you are putting it in, then it seems like you have an awfully weak gas pressure or obstruction in burners or something.

Or another something could be a real small furnace. How many square feet is your house, and how many btu's input and output is it rated at? It should have this listed on the manufacturere's plate inside the furnace.

But then I can't figure out that if either of these were the case, why the burner(s) would shut off, as then you would think it should not be overheating, either. Unless there is an overlap going on where no sooner does the burner shut off and a new call for heat occurs right away again, and for some other reason a malfunction occurs and goes into some lockout mode. Therefore to rule out the later, I need to know if the induecer motor ever shuts down, even for a short bit, during the duration.

With a little more dialogue back and forth, maybe this can get resolved by me or others, who are naturally welcome to jump in.
 
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Old 03-22-08, 02:02 PM
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Thanks again for your reply and correct me the typo.

It runs OK for over 10 years.
The furnace input BTU is 100,000 and output BTU is 80,000 for a hours over 2400 sf.

The flame was on all burner tubes when it started. After it runs about 30 minutes, the burner is shut off, but there is small flame in the middle near the ignitor and main blower and inducer are still on and never stop.

I changed new filter yesterday and things are getting a little better, meaning it runs longer.
 
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Old 03-22-08, 05:18 PM
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Huh. Can you feel a lot of air coming out of your registers, or not very much?

Is your filter clean?

And if you stick a thermometer down in one, say the closest to the furnace, what does it say after the furnace has been running say 10 minutes or so?

That residual flame sounds like the gas valve is not seating perfectly. I doubt that has anything to do with any other problem you are having.
 
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Old 03-22-08, 05:37 PM
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but there is small flame in the middle near the ignitor and main blower and inducer are still on and never stop.
That's normal if the furnace has intermittent pilot ignition and there's a problem with the circuit board. (ignition module or integrated control)
 
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Old 03-22-08, 06:27 PM
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Thanks Muggle and ecman51

Can I do any testing to see if the board is bad?
 
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Old 03-27-08, 06:14 PM
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problem is solved

problem is solved by changing a limit switch.
 
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