Furnace going into lock out

[concours]

Our 2013 cougar has a Suburban SF-30FQ furnace that intermittently locks out.
The furnace always ignites correctly ie the fan starts and runs for 15 seconds and then ignites and makes good heat however it occasionally stops as if the overheat limit switch has tripped the furnace stops and remains inop until its switched off and restarted.
The return air is clear, the air ducts are not restricted and the exterior intake and exhaust is not restricted.
The overheat limit switch connections are good and the switch has zero resistance cold.
Im suspecting a faulty high temp limit switch but open to any ideas

[JRTJH]

Faulty High Temp Limit Switch or possibly dust/dirt/pet hair on the squirrel cage fan louvers ???? There's no filter (by design) on the inlet air to the heat exchanger/fan and they will, at times, get dirty and hamper the airflow. Sometimes just cleaning the squirrel cage with a vacuum is all that's needed. Might be worth a try.

[chuckster57]

Limit switch is cheap enough to just replace and see what happens.

[concours]

I checked the fan etc for dirt and debris and it was good but I did still blow air thru it and vacuumed all the inlet vents but found very little, low and behold it worked perfectly all evening and thru the night and for a while this morning then quit and locked out. I just replaced the high temp switch and wait to see what happens. I hate intermittent problems

[concours]

Well the furnace finally quit so that I could diagnose what had been a very intermittent problem sometimes working for 3 days without a problem. The circuit board that had been tested many times was at fault. I replaced it with a Dinosaur board which appears to be a far better quality and has a longer warranty. all is go now

[JRTJH]

Thanks for the update. I've been sold on Dinosaur Electronics for at least the last 20 years. I won't use an OEM board if there's any way around it. Good to hear you're warm and the furnace is working well. Enjoy winter camping LOL

[concours]

Winter camping in Yuma isn't to hard to take lol

[Wingerdinger]

X2 on the Dinosaur board, I installed a new furnace in an old pop-up one time, and had nothing but problems when dry camping, until I swapped out the 'changed under warranty' OEM board for a Dinosaur. I got a good enough deal to justify it, and never had any further problems. As I recall, it wasn't a terrible price either.