Triton t50i used to be plenty hot enough with the temperature dial around
half way. Now it's only just hot enough turned fully up.

I'd replace the whole unit, but it is an obsolete model, and I don't want
to fit anything larger such as a t60i. So I'm planning to replace the can
as I assume it's scaled up (we have very hard water). Sound reasonable?

Should I replace the stabiliser valve while I'm at it?

If it is a buildup of scale, can I descale the 'old' can and keep it as a
spare?

Oh, flow rate is fine - Plenty of pressure. It popped it's PRD ages ago
because I hadn't descaled the shower head for ages. Occasionally it trips
it's MCB (maybe twice in the last year).

Any other possible causes that I haven't thought of?

Cheers,

Al.