It's always run 240V, I'm getting 120V at the black heater output and 0V at the red one - I checked and have 2x120V at the two inputs.
I'm beginning to think that one of the relays I used to replace the bad ones was bad too?
You wouldn't happen to know which of, I'm guessing, K2 or K3 powers which line? It's not clear from the schematic nor the circuit board - I suspect that it's K3 and that's the problem. Fortunately, I over ordered when I got the replacement power relays but it's not a trivial job to pull out the circuit board and remove/replace the relay again.
Before I did this I had 2 x 0V at both red and black at J9 - so I'm fairly sure it's the relay.