Recently replaced fan timer (midseason last year), similar symptoms again


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Old 11-15-13, 11:17 AM
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Recently replaced fan timer (midseason last year), similar symptoms again

The gas furnace is a ICP nugm100eha1. Last season I has the fan timer board replaced, the ignitor would turn on but the main blower wouldn't, only when the board was placed into continuous mode would the main burner kick in. Once replaced everything worked well, now I've noticed a couple of times where the furnace only blows cold air. Watching the ignition sequence it seems the same as last year; fan starts, ignitor lights waits 30sec (I think) then ignition system shuts down, air circulation keeps going. The furnace still works, I've only seen this occur twice so far, the furnace turned on fine just now. Could it be the limit switch, is there a way to isolate that for troubleshooting? The light code on the fan timer indicates no issue (the manual calls it heartbeat).
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Old 11-15-13, 12:39 PM
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Watching the ignition sequence it seems the same as last year; fan starts, ignitor lights waits 30sec (I think) then ignition system shuts down
That should cause a trouble code to come up on the board.

After the ignitor starts glowing..... it should be 30-45 seconds and then in one click of the control module.... the burner should light and the ignitor turns off. If your ignitor is turning off with out the burner coming on then the control board or gas valve may have a problem.

You can use a voltmeter to see if at that instant the gas valve is actually getting 24vac,
 
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Old 11-16-13, 08:24 PM
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Thanks, I will have to check again to make sure there is no error code when it actually happens (hasn't happened since). Is there a particular situation where that could happen very sporadically and not based on any hardware malfunction?
 
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Old 11-16-13, 09:48 PM
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Dirty/corroded wiring connections can cause intermittent problems.

Poor grounds to the control board and the burner can also cause issues. Make sure all screws for the module are clean and tight. Same for the visible burner mounting screws.
 
 

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