[skrobers]

Looking for some advise. The furnace stopped working in the following way. It got cold, so I turned the heat on. In looking at the furnace, there was a delay of around 7 minutes before the induction motor kicked on and the glow plug started to glow. The furnace would then ignite, but within 5 - 20 seconds, the induction sensor relay would click and the flame would go out. It would then try to re - light with the same results until I turn the furnace off. I did find that while the furnace was trying to stay on, if I unhooked the connectors to the induction sensor relay, and shorted them out, that the furnace would run for as long as I had the connection shorted. When I hooked the sensor back up, it went back to to the same on/off/on/off symptom....

My question is, what is failing. Is it a bad induction sensor, or is it possible that the induction motor is failing causing the sensor to turn off?

[#1 tech]

It is not the motor or the pressure switch. It sounds like its in the gas valve circuit. I belive it is timeing out when it does not prove flame. Do you have a meter? Check and see if you are getting 24V across the gas valve. It will happen after the ignitor fires. If so ohm out the gas valve if it is open then it's bad. If you do not have 24V at the valve back step to the board/relay and find the open switch. Remember rollout and high limit switches are there for a reason.