Just found this website and it looks right up my ally.
I have a Miller furnace (propane) that is acting up. The stat calls for heat. The purge motor kicks on, the ignigter lights up and the gas valve releases. The furnace fires up but goes back out after 6 sec's. It cycles like this two more times then lockout.
Heres the kicker, if I manualy turn on the blower fan (honeywell limit switch with manual feature) the furnace stays fired up and runs it's complete cycle.
What gives? I pulled the burner looking for a flame sensor but I think the igniter is pulling duble duty being the flame sensor also after ignition. Am I on the right track here? I need to get this furnace right today (off work and part stores open) as we have a baby in the house and I don't want to run the blower 24/7.