Power Shower switch melting



Super Minty Mod
My Satellite Setup
1200cc with 100,000,000,000 neurons and 100,000,000,000,000 connections
My Location
Fife, Scotland
I'm just back from a longer then expected stay with my parents, they have a Mira power shower and the switch for it outside the bathroom wasn't working properly.

About a year and a half ago the switch started making a squeaking noise when the shower was drawing a high current (with the shower on cold it was silent, as the heat was turned up the noise got louder). I changed the switch and the noises stopped.

This time the switch wasn't turning on, it felt loose as if the mechanism had come apart inside, so I took it apart to see. It hadn't come apart, but melted.

The most melted part is the neutral supply connector, the cable covering had even melted slightly an inch or so up the cable and become very thin where it pressed against the wall box. To me this is quite alarming, it doesn't look that far away from starting a fire.

The shower is either 8 or 9 KW (can't remember the model number to check it), the switch is rated at 45A and in the fuse box the shower circuit breaker is 40A.

I changed the switch for another one, but I'm worried that the same thing is going to happen again, has anyone seen anything like this before, or know what could be causing it?