York Diamond 80, intermittent fail to start or shut off early

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Old 02-12-12, 01:45 PM
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York Diamond 80, intermittent fail to start or shut off early

Furnace: York Diamond 80, approx 1997, natural gas
Location: Fairfax, VA
Thermostat: Brand new Honeywell (replaced yesterday)

Hi all. I'm seeing some intermittent ignition issues with my furnace which appear to be rapidly getting worse. Symptoms:

1. The ignitor always glows, but the burners don't always come on.
2. Even when they do come on, they will intermittently go out -- the time until they go out is getting shorter and shorter
3. Occasionally, after #2 happens, I will need to cut power to the unit to get the blower motor to turn off.

So far, I've replaced the thermostat and scrubbed the flame sensor with steel wool (I did this before I saw an instance of symptom #1). I've got a YouTube video of the whole shebang if it helps: Furnace trouble - YouTube

In the video, a failed start is around 30 seconds in, without doing anything to the system it tried again on its own and lit at around 2 minutes in.

Thanks for any suggestions.

Pete
 
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Old 02-12-12, 02:47 PM
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As is usually the case, your description of what is happening is incomplete and vague. You need to be more specific about what is happening.

For example, you rtefer to the "blower motor," but these days there are usually two fan motors on a furnace, the inducer motor which circulates the combustion gasses through the furnace and the fan that circulates heated air around the house. And just when are these fans turning on and shutting off --- both of them?

If the furnace is operating properly, the inducer motor will be switched on and remain operating anytime the thermostat calls for heat. When the thermostat is satisfied, the inducer motor and the burners are shut off at the same time.

So if the inducer motor and burners are shutting off together, you probably have a thermostat issue.

If the inducer motor keeps running when the burners shut off, you want to use a multimeter to see if the pressure switch is opening. If the pressure switch opens the inducer motor will keep running but the burners will shut off.
 
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Old 02-12-12, 02:55 PM
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look for a diagnostic flash code from an LED light on the control board.
 
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Old 02-12-12, 05:41 PM
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Just educated myself on the LED and where to find it by watching a video...unfortunately, it looks like mine is dead. I even opened up the lower door, stuck a flashlight in there, shut the door and ran the heater again to make 100% sure I was looking at the right thing. It doesn't light up at all.

Any other options or is it going to be too hard to diagnose without that?

Thanks for the replies.
 
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