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Old 01-02-2010, 09:48 PM   #1
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Honeywell 5yr old unit with no heat


I've had a problem with my Honeywell N8MPN/N8MPL or *8MPN/*8MPNL (not sure which one exactly, but thats what the manual says). Its a nat. gas furnace. Its about 5 years old (in a 5yr old house in southern california). Have been running the heat for a month, and starting 4 days ago for about 2 days, the blower motor was constantly running with no heat. I tried to turn it off using thermostat but it wouldn't turn off. I unplugged the thermostat, and the blower motor still ran. I turned it off at the circuit breaker. When I turned it back on, a day later, the blower stayed off. Turned on the heater and the thermostat said the heat was being turned on, the blower fan started but no heat.

Also there are two units (they both look identical), the problematic one is for the upstairs. I swapped the thermostats to rule out bad one but without success. (Little offtopic, there is a switch marked E & F on the back of the thermostat; Just curious what it means). I checked the fuse on the control board and its still good. But now the heater doesn't turn on when its set to heat. Does turn on when you set the Fan from Auto to On.

I tried to turn off the gas to see if the pilot turned on, but didn't hear/see anything happening at the pilot. It was then I noticed the flashing light on the Gas Control Valve. It was flashing twice, every few seconds. Looked it up on the manual and it says "Low Pressure switch closed when should be open".

Do the symptoms sound like the low pressure switch is bad? More importantly, did I do something wrong, warranty wise, by self diagnosing. My DIY mode kicks in without thinking. And should I call Honeywell or Local AC contractor (the one that installed it). Oh, I couldn't really find the replacement part (#1013529). Found something on ebay "Honeywell Furnace Air Pressure Switch 42-24196-02 0.80" (don't think the part # is honeywell's).

Anyway, thanks for reading and any info would be greatly appreciated.

Thanks

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Old 01-03-2010, 01:26 AM   #2
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Honeywell 5yr old unit with no heat


Looks like an ICP. Does the error clear when you remove a wire from the pressure switch?

http://icpindexing.mqgroup.com/docum...4108201100.pdf



Last edited by Houston204; 01-03-2010 at 10:28 AM.
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Old 01-09-2010, 10:25 PM   #3
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Honeywell 5yr old unit with no heat


Hey, thanks for the info. In this unit, the diag light is on the gas control valve, and not on the control board. Also I'm assuming there is only one pressure switch. If there are multiple, I'm looking only at the one that is mounted on its own, connected the combustion blower (rubber hose for the pressure), and power leads coming from the gas control valve panel.

When its flashing the code, and I unplug it, the flashing continues (twice then pause, twice etc.) without any change. If I unplug the AC and plug it in, when the pressure switch is connected or not, it does normal heartbeat for a minute, and then goes to flashing twice, etc. I swapped the pressure switch from the working one, and the pressure switches work fine on the working one, but neither work on the faulting one. So either I'm not looking at the right item, or something else is wrong.

Thanks
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Old 01-09-2010, 10:41 PM   #4
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Honeywell 5yr old unit with no heat


Does the gas valve number start with a SV ? Is the nipple on the inducer ,for the pressure switch hose, clear of obstructions?

Last edited by Marty S.; 01-09-2010 at 10:47 PM.
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Old 01-10-2010, 12:10 AM   #5
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Honeywell 5yr old unit with no heat


Quote:
Originally Posted by Marty S. View Post
Does the gas valve number start with a SV ? Is the nipple on the inducer ,for the pressure switch hose, clear of obstructions?
I'll go up there tomorrow to look at the valve number. Where would that be printed on? But the ICP part# is 1013350 for the gas valve. And about the pressure switch hose, when I had it off, I blew into it, and it was open.
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