Hi

I have the Keeprite 075 condensing gas furnace. Only about 10 years old.
Honeywell pro 8000 thermostat. NUGM100EHB1 is the furnace.

My question is what happened all of a sudden yesterday when I think I had a
bit too much humidity in the air, why did the furnace fail?

Now when there is a call for heat on the thermostat, what happens is both
blowers run only. The exhaust blower venting out runs immediately on start
up, the main house blower starts immediately on start up. But no clicking
from the honeywell smart valve, no sparking or ignighting beginning or
trying. Nothing else is happenening. No gas is going through the valve, no
obstructions in either intake or exhaust piping. I just vacuumed everything
out, I changed thermostates to the old one, same thing happens. I suspect
either the motherboard which has no lights to blink to show alarms, or the
gas valve which I had to replace couple years ago, But back then at least
the igniters would light up and shut off immediately, told me it was a gas
valve issue so replaced that and worked. All else looks clean and I smacked
as many relays as I could see, checked all the tubes to see if connections
are ok and seems ok. Even when thermostat is turned off, disconnected, when
I turn the furnace on it only immediately starts up the both blowers and
nothing else, no clicking, no safeties going on and off, no nothing. Anyone
here have a suggestion other than hiring an HVAC contracting firm to come in
and give me estimates? I know a board is about 50 bucks, easy to replace,
gas valve is about 150 easy to replace, what ever sensor should be cheap and
easy to replace. Any suggestions as to what to try next?

Thanks Hams, I know this is off topic, but I have gotten good advice from
this group before and there are no furnace newsgroups of any kind on my
server.
Thanks for any advice or tips or links
73