Check for the voltages in the breaker box. You can get faulty readings at the thermostats and individual breakers.

Turn off the breakers to all the individual circuits in the breaker box, then check for 240V across the main breaker. We had one leg of the 240V go out and if you don't turn off the individual breakers, you'll get some feed-through across the heaters and see 120V from the faulty leg to neutral or ground.

If you see 240V across the main, then start working your way "inward" from the main breaker to the individual breakers.