Originally Posted by tban
I turn the thermostat up, furnace starts to click but will not light.
If i go outside while it is clicking and put my hand over the vent (create
back pressure?) the furnace will light everytime. Sail switch problem?
Probably the sail switch, but it could be debris inside the chamber. Try taking the access cover off the burn chamber (just a couple screws hold it on) and clean out any flakes/debris that might be built up in there.