Lennox G24M3 Furnace
Original Board was Surelight 63K8901
Replacement Board is 83M00

First of all, I'm not sure what/if this qualifies as a DIY issue, so I'll post hoping some kind soul can help me figure this mystery out.

Originally, the problem was that the furnace (natural gas with no cooling hookup) would kick on when the t stat was calling for heating in the following sequence:

1) Purge motor turns on
2) Ignitor lights flames
3) Flames turn off after several seconds
4) Repeat step 1

The blower motor would never turned on and the flames would turn off (presumably on high limit). I tested all the limits, and they tested OK. This includes the primary limit in the heat exchanger, two rollout switches at the venturi, and the combustion air prove switch at the purge motor.

The blower motor worked fine when the t-stat fan control was manually switched to on. In addition the fan works fine when jumpered (all three speeds work), and the furnace would operate normally with a jumpered blower motor (of course with the exception that the blower was running 24/7). Therefore I concluded that the board must be bad and I replaced the board.

Now the furnace is doing the exact same thing as before with the new board installed but with one exception. The jumpered blower still works in all three speeds, however the furnace kicks the flames off even with the blower operating (it did not do this with the original board).

I am at a loss as where to go from here... any help at all would be appreciated. Thank you in advance!


Here is the schematic for the furnace: