Expert: Howard Livingston - 10/25/2009

Question
Thank you for looking at this question. I have a Honeywell Vision Pro TH8320U thermostat controlling a heat pump and oil fired furnace (as backup heat). Overnight temp setting is 62. Daytime setting is 68. When it is time to change from 62 to 68, the thermostat starts out with "heat on". Shortly after that the indicator changes to "aux heat on" - which I believe it is supposed to do because of the 6 degree spread in current versus desired temperature. My question is, with "aux heat on", should just the oil furnace be running (turn off heat pump and turn on oil furnace) or should both the heat pump and oil furnace be running?

Answer
First stage heat is from the outside unit. It is sensing that unit is not running. Check that out on a call for heat at a normal temp. Your oil furnace is 2nd stage. You may have some electric elements in the furnace for aux heat. If not, yes, the oil furnace should be on as aux heat. Check that outside unit tho.