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I have exactly the same question...
Could it be my thermostat? I have a 9 year old Rheem 90 Plus high-effeciency gas furnace that seems to cycle. The thermostat is a programmable digital Honeywell that I have programmed to set back at night. The problem is when the furnace turns back on early in the morning it seems to 'cycle'. The furnace will run for about 10 minutes, shut off to 2-3 minutes, and then turn back on for another 10 before shutting off again. I've noticed that the thermostat indicates that the system is 'on' even though the furnace if not running.
It's been doing this for 3 seasons. Last year and the year before I called 2 different HVAC companies and neither of them seemed to know what the problem was. They both disassembled a bunch of parts, but didn't find anything in particular wrong.
I've checked the gas pressure (gas company did that), and the electric (this furnace won't run if the electrical power polarity is wrong, and/or if it's not grounded.
The igniter is the electric glow type. It seems to light just fine.
Since the thermostat indicates that the system is 'on', but it's not, I was inclined to think the problem was the furnace. But, perhaps not. Any ideas?
Thanks! Daniel.
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