Hello gang. Need a little help if you don't mind. I have a no heat situation. My grandfather was an HVAC repairman for over 30 years and he is asleep already. Here is the scenario: Pilot is lit Filter has been replaced Thermostat works (swapped it with the one from upstairs that is working) The exhaust pipe is hotter than the fully operational unit sitting next to it. I still get no heat. Any thoughts? Thanks in advance.