Originally Posted by expedition1
Not sure if it is heat tape or a heat pump. My heat mode says Electric Heat. When in the electric heat mode the furnace now starts where as it never did before , unless the outside temps were close to the temps you stated.
In the zone that is working turn it to heat and turn up the temp. If the compressor kicks on it is a heat pump. If you start getting warm air and no compressor it is probably a heat strip.
The poster that mentioned a bad thermistor would proably be a very high candidate to check. If the thermistor is bad that could tell the thermostat it is colder outside than it is and have it automatically switch to gas. On my unit when it is under 30 it switches on the furnace even if it is on heat pump mode.