"John" wrote
| My mum has an electric shower (Mira Supreme, which according to the
| web is either an 8 or 9 Kw, I have yet to go and look at it) that
| has been in the house since new build in 1994. She is telling
| me the 'pressure' has decreased over the last few months, it
| still works OK to have a shower but "not as powerful as it was",

Is it possible that your mother is noticing the flow is decreasing because
it (both the weather generally, and the incoming water temperature) is
getting colder as we approach winter? If she's turning the temperature up to
get a hotter shower (or trying to keep the same output temp with colder
incoming water) then the flow will decrease.

If you turn the temp down then the flow should increase. If the flow is low
even at low temps, then suspect physical impediment to water flow.

Owain