Vcore 4 500mm heatbed stopped heating?

After 56 hours of total print time my bed has stopped heating. I've swapped the relay out of my vcore 3.1 and still it don't heat up. Without the bed being set a temperature it looks like the output of the relay is about 200v even when it's off! I tried re-wiring and moving things about and nothing has improved. In the end I took the bed out of my vcore 3.1 and wired it into the vcore 4 and on the relay output its reads 0v and then when set a temperature it reads 230v as expected.

Not really sure what to do next. Last night it had been printing fine. Went to print today and dead bed..

I wired the 500mm bed back in and with the bed heater set to 0c it reads 208v.