Furnace went Out


     It seems like as soon as I fix something around the house, something else breaks.  The furnace decided to stop working recently and I didn’t realize it until I woke up the next morning.  I decided to see if I could fix it seeing as I replaced the hot-surface ignitor the year before.  After watching the start-up of the furnace, I could see the ignitor was lighting the gas,  but would go out shortly after leaving the blower running.  After doing some research I figured it could be some oxidation build-up on the flame-sensor, giving the control board a false reading.  I removed the sensor and cleaned it with a green scouring pad until it appeared clean.  After replacing the sensor, the furnace seemed to work again and heated the house to the correct temperature.  About a day later I noticed the furnace had started to have the same problem again.  This time it seemed the flame would never light, even with the ignitor glowing hot.  Again I took to the internet for more information on how furnaces function.  Inside they seem pretty simple; a control board, gas valve, ignitor, blower & inducer motors, and various sensors.

After finding a flow diagram on the internet I began to try and troubleshoot the problem.  After a few hours I gave up and decided to call a repairman the next day (it was like 3am at this point).  The repair guy came, tested a few things and concluded it was the furnace control board; he said it would be around $300 to replace.  Knowing I could replace the board myself, I declined the service and just paid for a diagnostic fee, $49.  Next I called a friend who was able to get me a new control board for $79 right down the street from my house; all within 30 minutes of the repair guy leaving my house.

I began by first removing the old control board from the furnace.  Taking pictures allowed me to quickly record the orientation of the various wires attached to the old board.  Once everything was unplugged, I removed the old board from the furnace and set it too the side.  The new board looked to be of much better quality then the old one, and also had status LED’s, which the old one did not.  Once everything was replaced and reconnected I started the furnace up again….it did the same thing.

This time the board flashed the LED with an error code saying the pressure switch was malfunctioning.  I couldn’t get a new switch locally, so I called the another repair place since the first guy was wrong anyway.  After seeing what kind of switch it was, he located one nearby and had it installed in an hour for $100.  In the end I didn’t really need the control board, but it was nice having the status LED and I learned quite a bit about how a small gas furnace operates.

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