I have a Tempstar furnace and what is happening is the furnace will call for heat and the draft inducer motor will come on and after a momont I will hear the pressure switch go and nothing happens. The electric glow rod does not glow and the furnace does not fire but here is the catch the first time this happened I was looking around to see if there was any loose wiring and my flashlight went out so I hit the smart valve and the unit fired and ran. It will run on its own for a day or so and the problem will happen again.
I have will hit the smart valve and the unit will fire. I'm ussuming that the smart valve is bad. I know this may sound odd!
Thanks

Loose wires?

You should have a test terminal on the circuit board. Do the test the way you are told and see which function does not happen. I have an idea that it is the hot surface ignitor. Use a flashlight and shine it on the ignitor and see if you see a spot on it, it could be a dark spot with some white powder showing, if so this is a crack and it will have to be replaced. If you replace the ignitor do not touch the part that glows with your fingers, the oil in you fingers will shorten the life of the ignitor.