Furnace Not Coming On

Old 02-03-04, 05:52 PM
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Exclamation Furnace Not Coming On

I have an LP fired York Diamond 90 Furnace (Model# P3URB12N07501E) that is about two years old. I have been having a problem on and off for the last two months where the induced draft motor would come on, but the hot surface igniter would not energize. Turning the emergency switch off and then back on or opening the upper cover to the furnace would correct the problem. This would only happen a few times a month so I didn't pay much attention to it.

Today, the thermostat was calling for heat, but nothing was happening at the furnace except for a low hum. The furnace control diagnostics LED was flashing a code of two which the manual says, "This indicates that the normally open pressure switch contact are stuck in the closed position. The control confirms these contacts are open at the beginning of heat cycle. This would indicate a faulty pressure switch or mis-wiring."

The first time this happened I lightly tapped what I think is the pressure switch with a flashlight and a moment later the furnace fired up and ran normally.

The component I think is the pressure switch is shaped like a flat disc and is marked with a part number of "024-27637-00". There are two small hoses going to the part. The hose connections are marked "burner box" and "combustion blower". There are also two wires attached to it. One wire is blue and one is white.

Unfortunately the next time the thermostat called for heat the furnace went back to not starting and flashing the same code of two. Once again I tapped what I believe to be the pressure switch, but nothing happened. I continued to tap the switch progressively harder until after about four or five hard taps with the back of a flashlight I heard a click and again the furnace started up.

Is what I think is the pressure switch really the pressure switch? Do pressure switches generally just fail or can they limp along for a while? I know I need to get my furnace serviced, I just don't know if I can make it for a couple more days or if I need to call someone out tonight.
Old 02-03-04, 10:02 PM
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Do pressure switches generally just fail
Yes, I've replaced a few of them..

First, I would check to make sure those hose are clear, and not kinked. Remove the hose from the switch, and blow into them..

Also make sure you exhaust, and intake vents are clear.
Old 02-04-04, 09:31 AM
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You'll probably find the switch has gotten wet from condensation and has finally failed. Changing your filters often, or changing th type of filter you use could prove to eliminate the chance of this condensation accumulating in the future.

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