I have a Goodman furnace about 9 years old. The house is also 9 years old. It has been working okay for the last 2 years. Last week it started giving longer intervals between heating cycles i.e. it comes on for 20 minutes after every one hour. The service tech replaced the flame sensor and declared that the furnace is in excellent condition. After he went away the problem persisted. Called in another tech and he replaced the thermostat with a brand new digital Rodgers-White thermostat. I have set the desired setting at 78 deg F. The room temp of the room where the thermostat is installed is at 70 deg F. But the furnace is still not working. Any diagnosis or suggestions would be highly appreciated as I am in Toronto, Canada where the temp outside is -17 deg C (1.4 deg F)

Did he leave you a manual with the white rodgers tstat? Read it to see if settings can be changed,, or call the tstat installer to come back and make it right