We also have been having failures in the variable channels, but ours run up to 8 hours a day every day, so they get a lot of use and voltage run through them.
One problem we do have, when set to fixed, often they revert to variable on their own, which can be frustrating, explaining to those running to check if it has gone back to variable, and walking them through a reset to fixed. Do that 5 times (5 TIU's in super TIU) and it takes a bit.
