heat works intermittently

Old 02-09-07, 06:13 PM
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heat works intermittently

I have a RUUD Silhouette II gas furnace, and four times over this winter it has mysteriously stopped working. The first three times, it just didn't come on at all for 2-3 days, then it would run again normally as if nothing happened. I've checked the power to the unit and the voltage at the thermostat and both seem ok. While it wasn't working, the circuit board showed one solid green light (just a power indicator I think), and one blinking green light- it blinked four times, then paused, then repeated over and over- unless I moved the thermostat to a very low setting where it wouldn't be demanding heat, which would cease the blinking at the circuit board. I think this blinking is supposed to be related to my pressure valve.

Had a guy look at it today, he didn't do anything to test the pressure valve but didn't seem to think it was the problem. I didn't understand all of his logic but I think he's just assuming that if it were bad, it would remain nonfunctioning and not work intermittently. He recommended replacing the circuit board, but wanted $700 to do that. Before I do that, I wanted to know if there's a better way to be sure it's really the circuit board that's the problem. Is there some chance the pressure valve is actually the culprit?

BTW, this time he got the heat going again by jiggling every wire inside the unit, and unplugging and hooking back up most of the wiring harnesses that he could get his hands on. Didn't even have to disconnect the power to reset the unit in this process.

Should I prepare to own a new circuit board?

Old 02-09-07, 06:46 PM
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I'd want to be a little more convinced before replacing a control board. 4 flashes on your unit indicates the pressure switch was closed on start-up. The unit checks that the switch is open during the self test and makes sure it closes once the draft inducer starts.
Check to see if there is continuity across the common and normally open (n/o) connections of the pressure switch when the unit is off. If there is, then replace the pressure switch.
A stuck pressure switch will usually release when things are jiggled around. Here's some info about your furnace. Check out the t-shooting flow chart.


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