Eva Electric Shower Not Working?

We bought a property that had an Eva Electric shower installed. Since this was a weekend property we would typically turn the water off when we leave and turn off the power to the shower as well. Failure to turn off the power to the shower would result in our returning to a loud beeping noise. We assumed it was a low pressure warning. Turning the water back on resolved the issue.

On one occassion we forgot to turn the power to the shower off and returned to no beeping but no lights on the shower panel either. There is power getting to the shower itself but we cannot get it to work. Alas the way it is plumbed.. no power = no shower as no water will run at all.

Does anyone have any thoughts on this. A manual might help. I've been told the manufacturer is no longer in business.

Thanks in advance