Furnace will not remain on

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Old 11-10-08, 12:52 AM
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Furnace will not remain on

Hello, I'm new to the post. My Crown Boiler forced-air gas furnace will ignite and "flame on" then the blows. It "flames out" about 1 minute later but the blower will continue. It will "flame on" again for about 30 seconds then eventually stop blowing prior till reaching the set temperature. It will only restart when I power off/on the furnace switch. The model # is MDA 120 NH5R. Its an upflow furnance. I replaced the ignitor and the fan timer but it still does the same thing. Please help!!!!!! Thanks.
 
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Old 11-10-08, 06:56 AM
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Originally Posted by dag38 View Post
It will only restart when I power off/on the furnace switch.
Sounds like it is locking out on you.. Are you getting any fault code on the board?


replaced the ignitor and the fan timer
You do any trouble shooting before ordering these parts?
 
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Old 11-10-08, 08:44 AM
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What board are you referring to? .....the Fan Timer is the only board I see but I replaced that w/o trouble shooting.

I replace the ignitor because the ignitor rod/pin broke off. Can you explain 'lock out" ? Thanks for replying.
 
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Old 11-10-08, 10:49 AM
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How old is this furnace about?

I only could find info on the first three letters, I used that and came up with info about control board.

Are you able to post a photo of your system?
 
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Old 11-10-08, 01:34 PM
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Im not sure of the age but it seems to be only a few years. I do not know how to attach pics The icon is requesting a url as a link instead of a path.
 
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Old 11-10-08, 02:49 PM
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the photo has to be uploaded to a photo host site like imageshack, photobucket, or yahoo.
 
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Old 11-10-08, 04:45 PM
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What does the exhaust gas fan do when the fire goes out?

Lockout prevents the current from getting through the system so that it can no longer even TRY to ignite. It has figured that if 3 times of trying to ignite does not work, there is no sense keep trying and putting wear and tear on components, and even few-seconds puffs of raw gas, for no reason.
 
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Old 11-10-08, 08:48 PM
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[IMG][/IMG][IMG][/IMG]



The exhaust fan continues to blow until the system cools.
 
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Old 11-11-08, 07:59 AM
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Something is killing your flame. What the blower is doing is normal. The reason it shuts down after the second short flame on and off is the fact that the blower has been running, and the fact the heat (flame)shuts off, so therefore the heat exchanger temp will end up coming down low enough so the blower shuts off due to low heat exchanger temperature..

Have you tried to test to see if the 24 volts that comes into the pressure switch, then goes out the other wire, is shutting down? IF your pressure switch only has 2 wires, you can actually hook these 2 wires together, with jumper, to then see if the furnace runs then. This is just for test. Do not leave it this way!!

If you have an intermittant automatic pilot lighting system, these can be suspect in more ways than one. You need good pilot flame and you need the flame to be sensed by either a separate sensor or through the metal of the assembly itself, on back to the ignition control board which also has to be grounded. This work almost requires removal of the entire pilot assembly to clean up any rust and tarnish, inspect and clean out pilot orifice hole with perhaps a real thin wire brush wire strand you pluck out of a wire brush (needles/pins are too big).

And to clean up any burner flame sensor. If you have a seperate one, then remove it and clean the probe end with steel wool or scotchbrite pad.

Youi also want to make sure you do not have condensate water backed up at inducer and secondary heat exchanger. You need to remove drain tube and blow towards drain, reassemble, then blow back up the tube the other way back into the furnace.

You also want to make sure that the smaller rubber tube that goes from the pressure switch back into the furnace/inducer was on tight at each end, has no cracks, and is clear by removing tube and trying to ream out where it goes into the inducer.

One of these sysmptoms, if addressed, will likely fix your problem. Remove the pilot assembly, only if all the other things I listed do not help.
 
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