Thermal Zone Nordyne board cycling


Old 12-06-09, 10:46 AM
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Thermal Zone Nordyne board cycling

After searching the internet I have found nothing that will help. So here it goes.

I had a Thermal Zone gas furnace model # GU100M16B-S installed about four years ago. In that time I have had the board replaced twice. Nordyne board 624631-A.
Since the last replacement I noticed that the furnace will cycle 3-4 times before bringing the room temp up to what is set. The original board use to do this only if it was raising the temp 2 or more degrees. When I say cycle I mean that it will fire like it should and run for about 5 minutes and then shut the burner and blower off. The inducer motor starts running and so forth.

I have looked at the schematic for the new board and I don't see where there is anything that can be changed to "fix" this. It really isn't a problem but more of an annoyance. I am also thinking that the ignitor is going to wear out quicker.
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Old 12-06-09, 11:37 AM
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Did an actual furnace guy replace the boards and determine this was the cause of the maladies at hand?, for changing them? And was that malady the very one you have now? Did replacing the board actually stop that malady or did you sort of want to believe in your mind that it did, due to the expense? (That mental phenomenon can happen, you know).

How do you not know that the thermostat is at fault or the furnace is high limiting or a pressure switch is opening, let's say? Does the inducer motor also stop at that 5 minute time also, right when the burnmer shuts off?, or not?
Old 12-12-09, 04:20 PM
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The reason that they have been replaced was because I had no heat. As in the furnace would do nothing. Yes they were replaced by an HVAC pro.
I don't know if the original was a Nordyne board or not. I do know that the last two have been the same Nordyne board. I actually have the last one.
Since the only thing that has changed was the board I assumed that was probably what it was. If it might be something else then fire away. I'm not a HVAC guy.

The inducer motor is running when the burner and blower kick out. I have checked the light on the board and it stays stead during all cycles.

Is this all in my head? No, trust me this last board makes the furnace cycle numerous times and the old one would cycle once, maybe twice.
Old 12-12-09, 07:01 PM
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I had occasions where I replaced the furnace circuit board twice for the same customer. Had it been within a year I would have replaced it under my guarantee at no charge.

It's unfortunate when a manufacturer has a bum product, but usually you have to wait for the manufacturer to correct the problem.
Old 01-07-10, 12:01 PM
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Having this exact issue

I have this exact same issue with the same model furnace. On my system, the control board has never been replaced, but I changed out my thermostat which had no effect on the problem. Though, it is a much nicer thermostat.

Do you get an LED code on your board during the "premature cycling" process? I do not.

I would love to solve this problem...It's driving me crazy!
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