NTG9075FGA3 ignites for only a second before cycling again

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Old 02-09-16, 05:07 AM
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NTG9075FGA3 ignites for only a second before cycling again

Sequence:
Thermostats calls for heat
Draft inducer starts
Pressure switch functions properly
Pilot gas valve opens
Pilot lights properly
Main gas valve opens
Flame lights and immediately goes out before flame even has time to reach flame sensor.

This continue less for many cycles. I can do two things to make it light every time. I can either open the burn box and it will light or I can remove the vacuum tube from the Honeywell gas valve and gently blow into it and it will light and stay lit.

I have already verified there is not blockage in the drain system or vents. Any ideas?
 
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Old 02-09-16, 05:20 AM
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Oh, this started almost immediately after I had to replace the draft inducer which squealed several times loudly and then seized completely.
 
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Old 02-09-16, 09:53 AM
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Welcome to the forums.

As a guess..... you have a vacuum leak in the inducer. Possible bad/broken seal/gasket.
 
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Old 02-09-16, 04:15 PM
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<<As a guess..... you have a vacuum leak in the inducer. Possible bad/broken seal/gasket.>>



That seems very likely. If he sprays some water around where then inducer motor gasket fits, he may see the water being sucked into the inducer motor area....
 
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Old 02-10-16, 04:51 AM
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Alright, I found one problem (idiot me). I replaced the pressure switch as the old one was bad and I verified the new one was working, but I took the little plug out of the one side. I replaced that and it started working great, overnight. Then, this morning it is sowing the same thing.

I pulled the inducer off and the exhaust pipe above it was dripping water. Not sure if that is normal. It was a good bit of water. I'll check for leaks shortly.

Thanks all.
 
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Old 02-10-16, 12:14 PM
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You have a condensing gas furnace, which condenses water vapor produced by burning gas and condensing it into liquid water, recovering the latent heat in the process.

The furnace should have white PVC vent pipe if I'm correct.


Very likely the pressure switch isn;t staying closed reliably. When it opens, the main burners shut off. You should use a multimeter to verify that the pressure switch opening is causing the burners to shut off.


In a condensing furnace, a drain system is built in to drain away and dispose of the water produced by burning the gas. If that drainage system is plugged up, the furnace accumulates water which will impair the venting and cause the pressure switch to open.

You need to identify what is plugged up.

Since water is dripping from the vent pipe above the burners, you may have a sag in that plastic piping which will allow water to accumulate and create a puddle, which can easily cause the pressure switch to open.

So I'd check that first.

The vent pipe should be on a gradual slope so that water will drain back into the furnace and be disposed of through the furnace drainage system.

SOME dripping is normal.
 
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Old 02-10-16, 04:15 PM
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Thanks all, the 2 rubber seals on the inducer were torn to nothing. I replaced them and all is well. Thanks for the help!
 
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