Bel canto problems

Looking for guidance. I have several bel canto 600 ref m amps in a home theater set up. Two of the amps have had intermittent output problems which I ascribe to either overheating in the cabinet or a short internally. One of the amps actually is off more than on. (Btw the amp led is always on)
i have sent amps back to the factory and the problem amp back twice. Bel canto always says they are fine and then the problem starts right back up.
at this stage I would love to get out but the factory does not seem to know or care how to fix the amp (s). The amps were bought q4 2015 and have not worked right in two years. Any suggestions other than cursing the gods would be welcome. I used to be a big bel canto fan but this is pretty bad for amps that are considered high end.