Get an electrician (or plumber?) in to check it out.

In the meanwhile, you can try (workaround) turning down the temperature dial (if it has one) in increments of 20% or so, and see if that helps. It did at several of the B&Bs we've stayed at over there.

Theory being, that the water was too cold for the size of heater/circuit to keep up with, and the heater actually, well, overheats, and then shuts itself off for safety reasons.

A slightly lower output temperature can allow things to muddle by until the root cause is fixed.

Cheers