Suburban Furnace

On the newer models, if the sail switch is stuck closed the blower will not start. Unless you do not have an outside access door, there is really no need to tear it apart to troubleshoot- you can access everything needed with it in place.

First thing I would check is the spark gap on the DSI points.. but after that it gets expensive..

IF you narrow it down to the control board (I'm 50/50 on that, one time it was the gap and intermitent operation the next (complete no op) it was the board.

IF it is the board. Dinosaur boards are highly recommended, having one I understand why they are very well made.

Moved from General RV'ing forum.

Yep dirty contacts/terminals. Doesn't take much resistance to stop 12V DC.

Take cover off t-stat........disconnect the furnace wire and power wire & twist them together.
Furnace runs/lights off----problem with t-stat.

Does the blower motor start or not?
If not, do you hear a "click" in the furnace when the thermo tells it to start?

Might help...my thermostat made good contact and started (conducted elec to furnace) 70% of time and failed to start 30% of time. I cleaned up contacts and now furnace works 100%.

I tried all kinds of stuff (making sure wires were connected all the time, cleaned out combustion chamber, etc)

Somebody on here recommended to clean up contacts. Simple 30 sec job on old style thermostat and it solved the problem.