Would there happen to be a SINGLE pole thermostat in the circuit somewhere ahead of where you are testing as well as possibly another heater in the circuit after the thermostat still connected????..
I have seen this a few times where they use a single pole stat to break one of the hot legs of a heating circuit, which works effectively BUT when you test from any point in the circuit after the stat you will see 120V to ground, that is with the heater still connected across both legs... That will allow you to see 120V to ground on both legs but no 240V, as long as the stat is open.... Close the stat and you see 240 across both legs..
A.D
