Did the continuity test on the pressure switch, all good.
Cleaned the hole in the fan already as well.
Managed to find the error code, pointing to the thermostat.
I already replaced the old thermostat with one i had laying around (never used), and did not make a difference, would work for a few days and then crap out.
I assume i could have ywo bad thermostats, I guess.
Ill go buy a third one tomorrow and if nothing else I should be able to return it if it doesn't fix things ...