Can someone solve my electric shower problem?

[Goldberg]

Does the shower have dual heat setting ( selected by buttons on the shower)?

Of course it does:

If so, could it be that when your mate clamped the shower feed, the shower was on half power?

Of course it could.

If the shower is working correctly theres no resason to assume it will be drawing any less then 40A, and the circuit should be designed to take that.

There's every reason to know it:

9.5kw at 240v is just under 40A

not this shower as its rated @ 230v

No it isn't.

more like 43.1A @ 240

Nonsense. Does it not occur to you that shower manufacturers design their showers to work within the limits of the easily available CPDs?

A 9.5kW shower will take more than 32A so the fuse would blow eventually. If all was OK with the shower I would expect the fuse to last quite a while before blowing. If however there is a fault, it would blow quickly, with some noise or smell somewhere.

If your mate was reading 20 odd amps, I would suspect that the power was on half power or the meter reading incorrect.

Ideally for a 9.5kW shower you would need 10mm cable with a 40A breaker. Just fitting a 40A fuse or breaker on yours would be Ok for the shower but wouldn't protect the cable from overload. The cable would overheat before the fuse blows.

All of that has already been said.