Ruud Silhouette II Circuit Board bad??

Old 02-23-11, 06:55 AM
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Ruud Silhouette II Circuit Board bad??

About two weeks ago our furnace (1998) was lighting and then going out after ~5 secs. We had a technician look at it, clean it, clean the flame sensor, and was told that we need a new circuit board, due to the blower motor not kicking on, thus the furnace would shutdown. I am not sure I like this explanation.

Knowing a little about how the furnace works, I notice that the flame light on the circuit board never lights up. I know it used to because I would sit and watch the board and the sequence of events quite a bit whenever the furnace had issues in the past. It is logical to me that if the circuit board does not detect the flame the gas valve would shut off and I would see the results I am getting.

I noticed in the past few days that the metal from the thermocouple is very shiny and clean (he did clean it!!), so is it possible that the thermocouple sensor itself is bad? Is there a way to test this? They want to charge about $400 to replace the board.
Old 02-23-11, 09:21 AM
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The flame sensor is not a thermocouple.

Remove the cover that conceals the burner compartment of the furnace. Carefully describe the sequence of events which occur when you turn the thermostat up to call for heat, and post those here.
Old 02-23-11, 03:09 PM
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some of these units had problems with the mulex plug that goes between the blower deck and the combustion compartment. Best solution, cut the flame sensor wire on both side of the plug and route to blower compartment (typically there is a small hole close to the plug) and wire nut the two wires together, I've seen this a bunch and have beat myself up over trying to figure out what was going on as I would get signal at the board, but still had problems, replaced the board to find out it was the connector plug between the blower deck and burner compartment.

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