Gas and Oil Home Heating Furnaces - Should I replace the HSI Ignition Module

I think I should replace the Ignition module but I'd like to check with the board before forking out $100. I have a Trane XL90 with a Fenwal Ignition control module

The problem is now fixed but here were the symtoms:

1) The ignitor would start
2) After 40 seconds the gas would turn on
3) The gas would ignite but shut off after 5 seconds

After reading the boards I suspected the flame probe

1) There was no DC current flowing through (hence the shutoff after 5 seconds)
2) There was no AC voltage during the flame detection, but 140v where present for 10 seconds AFTER the gas was turned off

I suspected the control module. Opened it up (Fenwal 05-246266-203) and noticed that one 1k resistor and a diode had some signs of overheating. I unsoldered them to check them there were OK. I replace the resistor anyway, put everything back and now it is working!!!

I checked that:

1) AC is present now on the flame probe within 3 to 4 secs
2) The gas is turned off if I unplug the flame probe

So we should be safe for the upcomming days but, I think I have a marginal control module that will start acting soon again and I think I should replace it. Wadayathink?

Thanks

Jacques

I think you had a bad solder joint & now you don't. Just my humble opinion.

I am still surprised that the AC voltage is only showing up 3 to 4 seconds after the gas ignition. I'd expect it to start before the gas is turned on.