Problem solved. It turns out that it was a problem with how the
humidifier was wired. My HVAC buddy says the humidifier 24VDC was
pulling power from the wrong place in the furnace. It was likely
draining power from the furnace main control board caus...
I'm having the same issue. I also am starting to suspect it is the Nest
causing the furnace 33 error. I've checked several things on the furnace
itself. Going to run furnace without Nest manually like you did to test
the theory.
