Thanks for youre answer. My unit has been kleened like new. I also have increased the filter area by 30%. It buggs me that it can run 28 days 3to4 hours each and then crap out. I will check the filter tomorrow and let you know.
i have already raised the blower speeds. New clue-- the failure is the first 5 min after sitting all night on set back. Peter
ps maybe the blower is lazy out of the gate. maybe the high limit is not working causing the over temp to fail????