Comfortmaker ignites for a few minutes then shuts down?


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Old 12-21-09, 12:26 AM
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Comfortmaker ignites for a few minutes then shuts down?

I have a comfortmaker c9mpd100j (92%). The unit is 1 1/2 years old. After calling for heat the unit fires for a few minutes then shuts down. The LED code flashes 3 times. If I bypass the pressure swith the unit will run to the thermostat setting, stop as normal, then it will not refire if the thermostat calls for more heat(again this is during the bypass test). I've checked the following things:1) lp gas pressure switch, 2)disconected the exhaust and blew air through flue towards exterior(seems to be clear). Can the pressure switch be faulty? Or should I look for something else?
Thanks
 
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Old 12-21-09, 01:37 AM
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The furnace manual is at

http://www.radiantheatproducts.com/p...N9MPD-9MPD.pdf

The 3 flash diagnostic code is for a pressure switch being open when it should be closed.

The ignition module also has a test for the pressure switch being closed when it should be open. Leaving the jumper wire bypassing the pressure switch would probably trigger that safety check and result in the furnace not firing the second time.

When a pressure switch opens and causes the furnace to shut off, about 5% of the time it's a bad pressure switch and 95% of the time a defect in the furnace, vent or air supply that is restricting the flow of combustion air through the furnace.

The correct way to diagnose this problem is to measure the pressure being applied to the pressure switch, and then use that to identify what the problem is with the furnace.

Do you hear any sloshing noise of water being blown around inside the furnace by the inducer motor? That furnace has a lot of plumbing, any part of which can get plugged up.

Remove the air supply pipe to the furnace and the vent pipe from the furnace and see if the furnace turns on properly. If it does, you likely have a problem with one of those pipes.

If it doesn't, you likely have a problem in the furnace itself, with plugged up plumbing a likely cause of the problem, among a good many other things.
 
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Old 12-21-09, 07:54 AM
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new switch doesn't work

I just replaced the pressure switch with a new one and the unit will not ignite. Flashes the 3 light code.
I also removed the exhaust pipe and there are no blockages or laying water but condensation throughout.
 

Last edited by harley87; 12-21-09 at 08:16 AM.
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Old 12-21-09, 09:26 AM
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Originally Posted by harley87 View Post
I just replaced the pressure switch with a new one and the unit will not ignite. Flashes the 3 light code.

No surprise there. I tried to warn you against that. But people, even 'way too many "repairman" go for replacing pressure switches like a duck on a junebug.


You need to remove both the incoming air pipe and the exhaust vent pipe and see if the furnace will work with these possible sources of obstruction removed.
 
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Old 12-21-09, 09:29 AM
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It's also possible for the sampling port on the inducer motor housing to get plugged with rust or gunk. It's probably worth removing the rubber tubing and using a small drill bit to clean out that hole on the chance that could be the problem.
 
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Old 12-21-09, 09:53 AM
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After removing the exhaust flue and black tubing, I sucked out any laying water. The unit now will ignite, burn for a few minutes, kick off for about 3 minutes, then refire up and run, then repeat this same cycle.

After it kicks off and I remove the face plate I can notice a momentary sent of gas?Is this a different problem?

Also this unit doesn't have an incoming airtake pipe. It sucks from within the basement.
 

Last edited by harley87; 12-21-09 at 10:09 AM.
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Old 12-21-09, 12:47 PM
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With all of the recent snow in that part of the country I would suspect the vent termination may be buried in snow. Just a thought.
 
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Old 12-21-09, 07:37 PM
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Removed combustion blower, plastic housing, drain/vacuum lines, and exhaust line. Blew them out then replaced gaskets(all looked to be damp and corroded). And the unit is up and running like new.
Any idea why this occured or a way to prevent this in the future?

Thanks for all the tips.
 
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Old 12-22-09, 08:10 AM
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When you blew out the condensate lines, did you first feel back pressure when doing so, and then the line(s) became clear?

Pay attention to that next time. You can tell if you use your mouth to blow it out. You may not know anything what is going on if you use a compressor, because you will not feel anything.

Condensation forms in the secondary heat exchanger and is normally supposed to travel out a drain tube and also some goes through the ventor and falls out of the exhaust into the exhaust pipe/draintrap. If all that condensate can't drain, it can interfere with the tiny vacuum created when the inducer fan spins, and make it so the pressure switch, that senses that vacuum, shuts off. Very typical problem.

Why does it interfere with the vacuum draw? Because the air the ventor is pulling is going through the primary and secondary heat exchanger(to draw in fresh combustion air and then to exhaust the spent gases). If either of these become restricted, either with soot from a yellow flame, or in your case, condensate water, it can't draw air through the inducer as good! And if it can't? - the pressure switch can shut down, at any time during the cycle - and hence shut off the burner and leave the ventor running, as a tip-off clue. Often sparadically, in the early stages of plug-ups.

Did you understand Skips reply about the vent termination pipe may have gotten snow in it?, because you never responded nor asked more to learn more about that. If say snow was blocking that pipe, that also will stop the inducer from either drawing fresh air or expelling it and upset that necessary vauum for the safety pressure switch to work. Also, if say you condensate system was plugged and the snow melted and went down the flue pipe, even though it was no longer blocked, this could add to condesnate water that is plugging up the system. After big snowfalls, I bet that is one of thke biggest reasons for HVAC service calls about furnace not working, because of what Skip said. Some companies are good enough to advise you about this over the phone. Some maybe not and may cost you $70 or whatever just to have them point out or shovel snow from around it.
 
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Old 12-23-09, 07:34 AM
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We had about 4 inches of snowfall the night it shut down. My exhaust pipe was not restricted in anyway from snow. It runs horizontally out of the house and is about 24" off the ground with a 45 on the end. (Someone reccomended a 90 instead of the 45 what do you think?)

There was consendation throughout but I didn't notice a blockage and was paying attention to that detail. How about the gaskets being corroded? Could that affect the vacuum pressure?

Another thought: the unit is mounted horizontal, the exhausted vent runs out of the unit and ties into a Y which runs upward for exhaust and downward for condensation. Instead of a Y should it be a T so that there is not extra condensation building up in that short of a distance? I feel like the Y just may not let that condensation drip downward at the right moment. The installation manual shows a T.
 
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Old 12-23-09, 08:26 AM
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Follow the installation manual in all things.

It sounds like replacing the gaskets and cleaning out the lines solved your problem. It sounds like you nailed your problem with those repairs. Good job.

Asking about snow causing the problem was worthwhile, but it sounds like that was not a factor in the problems you had.
 
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Old 01-01-10, 09:38 PM
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What temperature should the forced air be at the registers when the unit is pushing air?
 
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Old 11-07-12, 09:08 PM
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Question Comfort maker condensation

Hello
i have similar issues in my furnace.
i have bypassed the pressure switch and the flame comes on every time, but using the switch I some times get 3 led flashes or some times lots of clicking and flame trying to come on and finally 6 and 2flashes.
i know its not the switch itself , the vents are clear and not blocked.
some times I hear slushy noise when this exhaust / induction motor is running.

i removed all the tubes big and small ones and noticed very damp. Also when I removed the motor I saw some rusting/ gunk in the gasket area and damp. Cleaned all still the same intermittent issues.

Also I noticed when blow tru the big tube I feel some pressure and bubbling sound when blow tru it . Not sure why this condensation is which is causing not enough vacuum to close the pressure switch. How to avoid this condensation.

thanks in advance
 
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Old 11-07-12, 09:41 PM
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Please don't revive an old thread. It becomes confusing and can result in bad advice.

My suggestion is to repost on a new thread.
 
 

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