What is causing false tube faults in VTL MB450 Series III?

Swap the tubes between the amps and see if the tube fault follows the set of tubes.

Have done that. Still same amp. Thanks

That’s strange. Have you isolated the amp from the preamp and speakers and repeated the power on sequence? Since the tube swap did not eliminate the problem, I suggest that you start from the basics…disconnect all things connected and start from scratch. Swap the power cord, if problem persists, swap to a new outlet, preferably, the one that your other amp is using. If problem still persists after having disconnected the speakers and preamp cables, and after swapping cords and/or outlets, then your amp is the culprit. If there are smaller signal tubes on the amp, repeat the tube swap process. Good luck. 

@michaeldouimette 

Seems obvious, but isn't VTL helping you troubleshoot this?

Guys, as the OP has already figured out, It appears to be the VTL tube monitoring/troubleshooting cirecuit that is at fault, giving false indications of a bad tube.  

I don't know how to troubleshoot this.

Jerry

If your experience with VTL service is anything like mine, good luck.  They could not have been less responsive and Bea said their service is backed up 6 months.  I live around LA so I took mine to George Meyer.  Two week and it was fine.

Jeez

George Meyer is great Place.

Just brought my monos in for a alignment ect.

They have the "Big" stuff there Saw the Big brother to your 450's there Woltan

and 10 tons more.