I have a Rheem Prestige Series gas furnace Model#RGFD-07EMCKS, MFD Date 09/2007 that has been running fine for several years. When I turned the furnace back on this fall it seemed to work fine at first but now it is cycling much too frequently in the morning when I have the temperature set increase from 60 to 68 degrees. It eventually reaches 68 degrees but it takes a couple hours, where in that past it would heat up the house in 10-15 minutes. It stays on for a few minutes and then turns off for a long time before coming back on for a few minutes.

I removed the Thermostat (HC TST401MDMS), turned off the furnace, connected the white wire to the red wire and then turned the furnace back on. The furnace code flashed "1-3" several times and then stayed at "h" . The burner is staying on but while it is on the blower cycles from, what sounds like full, for several minutes and then the blower decreases so that less air is coming out of the vents. The air is still warm and the code still says "h" during these blower cycles.

I have two questions:

1. Is the furnace acting normal when it cycles when bypassing the thermostat? If not, what should I do?

2. Is the cycling problem with the thermostat because of a problem with the thermostat or furnace? If it is the thermostat is it something that I can fix or do I just need to by a new thermostat? This model is very expensive. Are there alternative models that won't cost over $300? I don't have AC, just heat.

Thanks,
Peter