Ultra store water heater is tripping out

My Ultra store water heater is tripping out my Sargent PSU when I put it onto mains electric.  I think what may have happened is there was a power cut to a site I was staying at and when the electric was restored some type of damage may have occurred.  I was not aware until I went to another site CC and found the pole was tripping out and also my water heater trip on the PSU.  Along with a very helpful l warden we tested the cable from the pole and were able to establish it is the water heater that is causing the problem.  I am able to use it on gas no problems at all.  When I arrived home I confirmed the problem still exists when I push the on switch on the Sargent PSU panel it trips out.  Both the space heater and charger are working fine so I just keep the water heater off.  Any thoughts on what could be wrong or what else to check?  I did have a look at the rear of the Sargent PSU with a view to swapping the cables just to establish if it is the water heater or in fact the PSU that may be at fault? But not the same type of connections.

Thanks