Breckwell P22 Shutting Down

I've been running a Breckwell P22 for 3 years. For the past several weeks, the stove has been running off a thermostat in the on/off mode with no problems. During the last 24 hours, the stove has shut itself down several times before the temp on the thermostat was satisfied and the #2 light was blinking. I went through the trouble shooting section in the owners manual and started eliminating reasons. Airflow switch hose, inlet, burn pot, blowers, and exhaust are clean. Both motors are running and continue to run until the the stove cools and then they shut off -- in short, they are both getting power. Air switch was tested per instructions and appears fine. Four hours ago, I set the stove to manual (always on) and it's still running. The thermostat I use is a simple, millivolt, slide switch and appears to be working with no problem. Looks to me like the control panel is having trouble in the on/off setting.
Does anyone have any other thoughts before I spring for a new control panel?

Thanks for the suggestions. The the stove has been running in manual mode for about 15 hours with no issues. I think this rules out issues with the seals or any other "leaks".
When in the "on/off" mode, it runs for about an hour before it shuts down. During this time, I am able to turn the stove on or off by sliding the thermostat up or down --- I think this rules out any wiring issues.
I guess I can try it on the hi/low setting to see what happens.
I will update when done.

Yes. The stove was cleaned thoroughly in prep for this season. Like I said, the stove has been running in manual mode for 15+ hours with no problem.... isn't that a good indicator that it's not an issue with buildup or air flow?

good suggestion about getting the board repaired. Does anyone have any ideas where I can get a control board repaired?

Didn't see this one coming. The stove is running on the hi/lo setting using the thermostat. This time I noticed a pretty significant flame when running on high and barely staying lit when on low -- just didn't look right so I gave it another cleaning and noticed a lot of crusty build up in the burn pot. Apparently my pellet supplier changed from 100% hardwood to and 80/20 mix of hardwood and softwood. My best guess is that it was just burning too hot on the high setting and the high limit switch shut it down. A minor adjustment to the damper seems to have corrected the problem. The trouble shooting guide in the manual never gave this as a possibility. Running for 8+ hours on the thermostat - good flame, clean burn pot, warm house. I'll keep the $300 for a new control board in my pocket.