Hot surface ignitor backfed


Old 04-13-13, 02:56 PM
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Hot surface ignitor backfed

Hello to all! I am a new member on this site. Received call from Homeowner to troubleshoot furnace. Homeowner disconnected ignitor and used a piece of wire to jumped out plug that ignitor was plugged into, and get gas to stay on to verify ignitor was bad. Owner Indicated hearing a pop. i am an electrician by trade and don't claim to be a furnace expert. I have had some experience troubleshooting though, as I own a couple of rental properties. I tested ignitor with a continuity tester and had no continuity. It seems possible that owner backfed the control board and popped a relay by using the jumper wire thus sending 110 volts back to the board. The board had 24 volts, but i,m not sure if the relay can be replaced, or He just needs a new board. Thanks for any advice.
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Old 04-13-13, 06:43 PM
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Welcome tld38.

If a component on a circuit board is fried, the entire board needs to be replaced. To those of us in the HVAC trade, repairing a board is akin to you repairing an AFCI breaker.

What the homeowner did by installing that jumper was to create a dead short. The ignitor is fed 120V & when it was powered he had a dead short to the neutral.
Old 04-13-13, 06:47 PM
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Shorting the wires is obviously a bad move. Check the circuit board for a small, automotive type fuse. If he was lucky, he may have just blown it.

More info on the make and model of the furnace would help.
Old 04-14-13, 01:03 AM
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Thanks to all. I have not been back to owners house since yesterday. I had him call the furnace company since they carry many parts. I did test the ignitor and found that that was bad. I think he may have burned out the board by backfeeding it though. I will learn more later. My understanding is that the board is what controls the ignitor to fire, on a call for heat. So in essence, I believe he probably burned out the 24 volt relay that controls 110 volts to the ignitor. I don't know if this fuse would protect in this instance since it usually only protects the ungrounded , or hot side. Thanks again.
Old 04-14-13, 11:50 AM
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No....there isn't a fuse on that board that protects it from a short like that.

The relay is vaporized or the relay is welded shut or a foil is burned off the control board.

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