Electrician advice

[Meldrew2]

Almost certainly loose termination... with 6mm and 10mm T&E being multi-stranded, it is important to not disturb the gentle twist of the strands and then clamp the cable cores firmly. Having a strand out of place can make for a less firm connection and condensation can only make things worse.

Check cable size and shower rating - but in general a shower fault will cause the circuit breaker to "blow" before any cable / connection damage is caused, provided of course that shower, cable and breaker have been selected correctly.

Of course, if the shower was originally an 8.5kw unit and has been replaced by a more powerful unit, all bets are off...