I have a dual Lennox heat pump (14HPX), gas furnace (G40UH(X) system. Units were installed in 2010. All worked fine until October 2013, then gas furnace failed to come on when outside temperature was < 40 F.

System is supposed to switch seamlessly from heat pump to gas furnace when the balance point is reached. It does not do so. In order to get the gas furnace to work, we have to change the System switch from Auto to Emergency (EM) Heat.

On warmer mornings, with the outside temperature >40 F, the heat pump (which is outside) supplies warm air. On colder mornings, the heat pump won't work and the gas furnace (in the garage) won't kick in automatically, so we wake to a COLD house.

I've checked the LEDs, and they indicate power on (simultaneous slow flash), but no heating demand initiated from the programmable thermostat. When we select EM heat, the LEDS show a simultaneous fast flash, and we're getting heat from the gas furnace (because the heat pump is by-passed).

Any ideas on what's causing this problem greatly appreciated.