Hello all. I have a Gibson forced air furnace I've been having trouble with the last couple of days. At first, the unit would start up... Inducer comes on, about 20 sec later the ignition coil starts to glow, the gas would turn on and ignite and it would run for a short period. There is an amber colored light (not the red status light) on the circuit board that was flashing. After some research, it sounded just like the flame sensor so I took it out, used some sand paper to clean it up, put it back in. When I switched it on, everything seemed to work fine, as before, and the unit stayed on. The amber light was no longer flashing, so I had assumed it was related to the flame sensor and that cleaning it corrected the problem.

Fast forward to now a couple of days later. Had sporadic trouble with it yesterday, but after switching the unit off then back on it came back to life and worked fine all day. Last night it stopped worked again. Switching it off then on got it worked for a few minutes but then it went out again. Fortunately the symptoms have gotten more clear.

The inducer blower fan turns on, the ignition coil glows, but the flame doesn't ignite. At this point, the red status light blinks three times, which looks like that means the pressure switch is open with inducer on. Based on another post of the same error code, I switched the unit off, unplugged one of the wires on the pressure switch, then switched the unit on, waited a few seconds and plugged the wire back into the pressure switch. The ignition coil glowed, and this time the flame did ignite for a few minutes. I went back out after five minutes and the flame was off, and the status light was again blinking the 3 blink code.

At this point I'm wondering if I just need to replace the pressure switch, or if there is something else I should do or check. I'd love to fix this myself if possible, but if this is getting into the realm where I should call in a pro due to safety concerns, I'd like to hear that also. Thanks.

Well, I just found the installation instructions for the furnace, and it looks like the error code I'm getting now is actually 'pressure switch closed with inducer off' instead of what I thought based on feedback elsewhere here. I was also looking for a condensate trap based on other posts, but all I see is a tube that runs from the inducer to the pressure switch. I don't see any other tubes. I did remove the tube from the inducer to the pressure switch to verify it didn't have any water in it.

You might remove hose on the pressure and inspect for dry rot or cracks, did you blow through it to make sure its not clogged ,and that it fits tight on both ends when reinstalled

I did remove the hose. It looked fine for the most part. I did see a crack at one end but think I may have done that trying to remove it from the inducer nipple. I can blow through the hose fine... no clogs there. When I blow into the pressure switch, it is definitely closed off. When I suck I can suck air through and hear it click, so it will open and close. After doing this, it acts just as before. When I turn the main switch on, the inducer will start up, about 20 sec later the ingniter will glow. Sometimes the gas will turn on and ignite the flame but it will only last anywhere from one sec to a few minutes before it goes out and blinks the same three status light code, which according to the manual I have is "pressure switch closed with inducer off" even though the inducer is definitely running.

Did some additional checking after more research. First off, I blew into the inducer just to make sure it wasn't clogged at the inducer nipple, and it was not. I was able to blow just fine. Keep in mind I'm not a pro (obviously) but I used a meter, placing a lead on each of the two nodes of the pressure switch (with the main power switch off mind you) and set my meter to measure resistance in ohms (set to the 20M setting on my meter) When doing nothing, the meter read 1. When I suck on the line the reading would go to 0. When I stopped sucking, it would jump back up to 1. Next I replaced the wires to the pressure switch, attached a lead from my meter to one of the nodes, and the other to ground, set my meter to 200 AC, then switched on the main power. The inducer came on and I was reading about 25v on my meter.

Based on that info, I would interpret that as no clogs in the line--there is only one tube that I can see and it runs from inducer to pressure switch. I thought it was the pressure switch but I'm getting what I think is proper results when checking the resistance on the pressure switch and I seem to be getting proper voltage between the pressure switch and main board. So, either I'm misinterpreting, I didn't do one of the tests properly, or it's something else. I just don't know what else to do.

Well, it may be time for a service call. However, if the code was indeed blinking Pressure switch closed with draft inducer off, then a new pressure switch would be my next step.