I have a Bixby 115. If I turn heat level past 4 it shuts down with a 3 light blinking.
I have checked and cleaned stove pipe, flue cap, exhaust fan, and done all the recommended cleaning. It periodically has a 2-3 light condition but seems to run fine with it. Stove runs just fine for up to a week between cleanings as long as I keep the thermostat at 4 or bellow.

Remove the side panels and/or filter temporarily and see if the prob persists. A blocked or excessively dense filter can cause a #3.

If your stove is of approx 2005 vintage, check the R36 resistor, which sets the sensitivity of the fault detection. Early stoves were too sensitive, and a simple fix was made by changing the resistance. It is explained here: forum.iburncorn.com/wiki/index.php/Bixby#Light_.233 along with other possible causes of the #3 shutdown.

Corny:

Thanks for the hint. I do have one of those 'better' filters on the stove. I will remove it temporarily (and replace it with an economy one) and try upping the level past 4 as soon as the air temp outside cools down again so I need it.

We had some below zero weather and I was able to burn on level 7 for 3 days straight. Thanks again for the help.

Thanks for closing the loop, burnsy. I'm glad that it worked out and that the fix was cheap and easy. Reminds me that I should be attending to my own filter soon. Happy burning.