I own a Bryant Plus 80 gas furnace. The fan will run if I set the thermostat to "Fan On" instead of "Fan Auto". But the burners will not ignite. I have followed the user manual instructions to re-start the furnace, but that didn't work. I have a gas water heater and it is heating so I know the gas supply is okay. Is there something like an ignitor switch that I can fix? I'd like to avoid paying $100 to have someone come out to my house.