I bought my house, and noticed that the furnace would run for 15 min, then turn off for 15 min, and continue doing that. It appears to me that this could be a thermostat problem. Shouldn't the air or heat run longer then 15 minutes at a time, and stay off longer also? I have tried different temperature settings on the thermostat, but it doesn't help. I was thinking of replacing the thermostat, and see if this corrects the problem. The thermostat is located in the hall, and there is no vent located by it to make it turn off earlier then it should.