Gainsborough ambassador shower
 

Hi

My wife noticed that the thermostatic gainsborough ambassador shower
was dripping from around the dial today, so I removed the cover to
identify where the water was coming from (with the water supply off).

However, as soon as I turned it back on again the centre dial of the
thermostatic cartridge flew out with the pressure of the water, and
now I can't reassemble it in any way which actually allows the shower
to turn off. It is permanently on!!

The part in question is the very tip of this
http://www.gainsboroughshowers.co.uk...r-Concealed/7/

Does anyone have any experience with the "right" way to reassemble?
The dial seems to fit onto a pink threaded plunger which inserts
through the thermo cartridge.

Failing that, how simple would changing the cartridge likely be?
Simply a matter of unscrewing the existing one and replacing with a
new one?

THanks in advance for any help!

Matt