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.
I have two 600m in a cabinet under my Oppo for 6 months and never even turned them off since purchase. So far no problems. They just get warm never hot. Just try swapping them around to help isolate the problem. If one is really bad I can’t believe that Bel Canto would not step up to help you figure it out. Intermittent problems are really a pain sometimes. Good luck.
I never heard of Bel Canto not stepping up their game to resolve a product defect for a customer. I recommend having a friend test the suspected amp in his system. If he confirms the suspected defect, then get on Bel Canto to resolve the issue. If he can’t confirm the suspected defect (that is, it performs normally as Bel Canto claims), then it’s something about your home theater setup.  
Agree with colander 

which power cord are you using? 
Using any power isolaters? Power Conditioners? Etc 
wall outlet ok? Using the same outlet for other uses that may interfere?
are the impedances b/w amp and preAmp a goood match?
etc etc
Heat is an issue and I am experimenting w amps outside the cabinet. Interestingly, the 150s and one of the ref 600 m amps have been fine in the cabinet the entire time.
The 150's and one of the 600's that don't turn off could have a slightly higher temp threshold (Thermistor spec variations) before turning off.

Cheers George