[jsb5717]

First, if it’s below 40 degrees outside then your heat pump isn’t of much use. You will definitely need the gas furnace. So let’s focus on the gas furnace. There are a number of potential causes for those symptoms. But, let’s make sure we understand the symptoms. The sequence of events is important. So what exactly is happening? Do one of the following describe it?

You set the thermostat to call for heat from the furnace and:

1. The fan spins up for a few seconds then quits - if it’s this one then start by replacing the sail switch
2. The fan spins up then you can hear the igniter working. You hear it sparking but it doesn’t ignite. - if it’s this one then the sail switch is fine and there are other possible causes
3. The fan spins up, you can hear the igniter working, the furnace fires for a few seconds then quits. - if it’s this one then again, the sail switch is fine and there are other causes.

Let us know which number represents your symptoms and we’ll take it from there.