"Dave" wrote in message
...

what's the MCB rate at ?
how many kilowatts is the shower ?

It's marker B40 - and shower is 9.6kW. The booklet that came with it says
use
mcb 40/45A.

MCB rating is right on the limit (9.6Kw = 40Amps)

Think I've found the trouble though. The copper link that feeds into
the mcb has cracked through but was still making some sort of contact. The
heat
generated has melted some mcb case (!) All is isolated now and I'm off to
get
some new parts tomorrow. I think the copper link cracked as it was folded
at
quite an angle there.

That usually means the MCB wasn't attached to the DIN rail
properly.
You need to look at the cable, it should be 10mm with
a 45Amp MCB
While shopping buy an RCD if you haven't already got one.