Goodman GMP100-4 heat exchanger replacement?


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Old 11-22-10, 10:45 AM
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Goodman GMP100-4 heat exchanger replacement?

I have a Goodman GMP100-4 furnace which is about 13 years old. It seems to have a bad rep, although I've never had any issues with it until recently. The furnace stopped working because one of the rollout switches kept tripping. I looked into it, and found that the heat exchanger was cracked at two of the holes where the burners enter. I called up Goodman, who told me that the heat exchanger was still under warranty, so I searched for a contractor.
I called the first Goodman dealer on their list (who was also the original installer), who promptly told me that the furnace was cr*p (direct quote). He quoted $900 (labor only), and then tried to sell me a new furnace. I hung up.
I seemed to see posting somewhere that the time to replace the exchanger was around 2 hours. In looking at it, it looks like the burner/valve/ignitor can come out as an assembly, and then the exchanger can be pulled out from the front. That would fit with the 2 hour job time.
Is there some place that shows the steps involved with replacing a heat exchanger (preferably for my model)? Mechanically, it seems straightforward...

Thanks!
 
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Old 11-22-10, 03:36 PM
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Usually there are no guides on how to replace a heat exchanger.

Usually you have to pretty much tear the whole furnace apart. That's not too bad.

Putting it back together again can be a challenge.


I would recommend against it as a DIY job. But it's up to you.

Usually if you can get the heat exchangers for free under warrentee it's worth paying for the labor to install them, is my rule of thumb.

No harm in shopping around some more to see if you can get a better bid on the job.
 
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Old 11-22-10, 05:26 PM
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Thanks. I'm trying to find a contractor willing to do it. Most just want to sell a new furnace. I'm pretty mechanically adept, and it looks straightforward; my main concern is being able to seal the gas line correctly (big worry for me).
The issue with the furnace is that the flame rollout switch keeps tripping. It runs fine if I leave the door off, but trips when covered; I'm guess the extra air keeps it cool enough not to trip. When I look at it, I see flames coming out of the burner holes, and a couple of them have started to crack, which is why I think the exchanger needs replacement. That seems wrong, and what might be causing the rollout switch to trip, but the service instructions don't indicate any adjustment to resolve it.
 
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Old 11-22-10, 08:11 PM
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A frequent contributing cause of heat exchanger failure is an overfired furnace. The amount of gas burned can be adjusted. If it's more than the BTUs the furnace is rated for that can be a cause of a failed heat exchanger.

That's something I'd check in the process of replacing the heat exchangers.
 
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Old 11-22-10, 08:31 PM
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Originally Posted by SeattlePioneer
A frequent contributing cause of heat exchanger failure is an overfired furnace. The amount of gas burned can be adjusted. If it's more than the BTUs the furnace is rated for that can be a cause of a failed heat exchanger.

That's something I'd check in the process of replacing the heat exchangers.

Sorry to step in here but what type of gaz supply did the OP have ? If the OP have Propane Gaz then sound like the one of the regulator is getting bonkers but if that the case It will be wise to get a tech person with proper equiment to check the LP pressure but Natural Gaz it will be wise to check it as well.

Merci.
Marc
 
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Old 11-23-10, 01:13 PM
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The furnace is natural gas. I took a closer look last night, and I think the flames are supposed to be where they are (outside the exchanger), as the ignitor is just shortly before the flames. Thanks for the comments about adjusting the flame. I saw in the service manual about adjusting the regulator, and I will check the pressure. I hope to fix it soon, as it was below 20F last night; brrrrrr......
 
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Old 11-23-10, 08:10 PM
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Humm ., to adjust the gaz pressure you will need a manometer to read the numbers of inches water colloum but any adjustment I rather defered to the HVAC pros they will know excatally where to dail in with gaz pressure.

Don't get me wrong on this part that is only one part of test and there will be few other test equiment it need to verify the burner performace you can NOT just look at the flame if correct burning pattern etc etc there is too many varations to get involded in here.

SP do you have any thing else to comment due this is your turf { sorry to step on your turf }

Merci.
Marc
 
 

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