Ducane Gas Furnace shutting off prematurely

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  #1  
Old 02-18-20, 08:48 PM
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Ducane Gas Furnace shutting off prematurely

Hi all,

HVAC newbie, so bear with me.

My garage is heated with a Ducane CMPE075U2 forced air gas furnace. I have it set to a minimum temp of 45 degrees.

Yesterday, I noticed the furnace wasn't working at all and it was much cooler. Two years ago, that happened and it turned out there was ice in the system. Once we melted the ice in the rubber tube, and reconnected it, all was perfect.

This time, when I reconnect it and set for 72 degrees, it runs for about 5 minutes, and heats it up a little, then shuts down. Nowhere near 72 degrees. If I turn the system off, then on again, it'll heat up a few more degrees, then turn off again.

No error lights flashing.

Any preliminary thoughts?

Thanks!
 

Last edited by Andrew Lanzo; 02-18-20 at 09:08 PM.
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  #2  
Old 02-19-20, 07:34 AM
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Check for an active call at the furnace with your meter when it fails to run.
45 is too cold of a setpoint. That will damage or destroy a condensing furnace. Leave it set to a minimum of 60 F.
 
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Old 02-19-20, 01:08 PM
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Perhaps the last 7-8 years at 45 degrees has finally taken its toll on the poor thing

TOTAL newbie, so I literally don't even know what an "active call" is, lol.
 
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Old 02-19-20, 02:18 PM
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An active call is when the thermostat calls for the furnace to come on and run.
Running that long with that low of a setpoint, you may want to get the furnace serviced and checked to see if the primary heat exchanger has rotted out.
 
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Old 02-19-20, 06:05 PM
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I can't find a service manual for that furnace.

You need to observe the operation closer.
Does the main blower come on in the first minute or two or firing ?
Does it shut off or does it keep running and the burner shuts off ?
It almost sounds like an overheating problem.
 
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Old 02-19-20, 06:31 PM
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HI PJ,

The main blower *does* come on within a minute or two. After 2-3 minutes of blowing hot air, the whole thing shuts down. So, here's the update, which I assume will shed light on the issue:

At first, I could get the blower to start up again by shutting the whole system off and turning it back on. Now it won't even do that.

The water from the unit would usually drain down this hose (picture attached) that had always been attached via an external white box. Now, the water seems to be collecting in the highlighted white box instead...If I disconnect the white box (apologies, don't know what it's called), it seems to have a substantial amount of water within it.

https://imgur.com/a/D5P9xlR

If I then reconnect the white box, the furnace will go again, but it'll fill up with water, and we'd start all over.

thoughts?

(and thanks ppl!!)
 
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Old 02-19-20, 07:00 PM
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That’s the trap. It should have water in it but it needs to be able to drain. Check the drain line.
By the way, in your photo, which way is up? It almost looks like the furnace is laying on its back.
 
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Old 02-19-20, 07:23 PM
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Drain line appears just fine. I'm wondering if the trap itself might have an issue of some sort?

And in the photo, up is at the top. This is how it was when we bought the house...not even sure if using a forced-air furnace in a garage is ideal or not, but it's work well until now!

 
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Old 02-19-20, 07:29 PM
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It’ll work fine in the garage but only if set to 55-60 or higher.
Set to 45 will kill it.
Horizontal mount is fine. The trap will gather and retain water. That’s normal. But it needs to be able to drain out to whatever it’s attached to drain into.
 
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Old 02-19-20, 07:41 PM
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So without any easy-to-spot issue, should I just pay to have it serviced to figure out why it suddenly decided to only work for 3 minutes at a time? (then keep it at 55 from now on!)

 
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Old 02-19-20, 08:04 PM
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Depends. Do you have a meter and are you willing to get into the furnace further? This may mean working with live electricity.
 
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Old 02-19-20, 08:24 PM
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I do have a meter and I'm fine with electrical, except I wouldn't know anything about HVAC. Something simple to check?

 
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Old 02-19-20, 08:26 PM
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Since you say nothing runs at the moment, check for line voltage. Then check for control voltage. Then check for an active call from the thermostat.
 
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Old 02-19-20, 09:03 PM
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I should clarify. It'll run if I turn the system off, drain the trap, then turn it back on. It'll run for 3-5 mins or so, heat up the garage a few degrees, then turn off again.

 
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Old 02-19-20, 09:11 PM
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Then what error is it shutting down on?
 
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