[tyeboe]

Looking for help on an intermittent problem with my furnace failing to fire. Upon calling for heat, the usual sequence of exhaust, burner fire, main blower start after 15-20 seconds. Sometimes when call for heat is made, the exhaust blower and the main blower start simultaneously and the burner doesn't light. The result is the main blower runs continuously because the stat is never satisfied. Removing the call for heat at this point causes the main blower to stop after ~30 seconds.
I have not observed any codes yet.
Any ideas on which failed component would make the blowers start simultaneously?
Anyone know the codes for this furnace ?
Thanks very much for your help.

Ronnie

 

[user_12345a]

diagnostic codes can be fan on the schematic if the board has a led for that purpose.

 

[supers05]

Sounds like one of the safeties is opening. My guess is the main limit, or blocked flue/spillage limit. When this occurs again, check for voltage with a multimeter, across the safeties, the to one of the leads to the case. Report your findings

Cheers!