Gary wrote:
I think ours is on the way out. It doesn't really get hot any more
despite the hot water temperature in the taps being more than hot
enough.

It's gravity fed from the hot water tank and a header tank in the loft
(fairly certain of this). I'm not sure what model the shower is as it
was fitted by the builders when the house was built 6 years ago. This
means it was probably cheap.

How easy are these kind of things to change? For one who knows
nothing of matters plumb?

It could well be scale as others have said, but if you want to change them;

Turn the water off. Go up into the loft & find the big cold water tank.
There may be a stop cock on the pipe going in (the one connected to the
float valve). If so, turn it off. If not place a piece of wood across the
tank & tie the float arm up with string so no water enters the tank.

Now open the cold taps in the bathroom & wait till no more water comes out -
can take 15-20 mins with a big tank.

When no more water comes out, open the hot taps. Water should stop in a few
mins.

If over bath, remove bath panel, or gain access to back of pipes. Buy one
of these http://www.wickes.co.uk/invt/500535 or one of these
http://www.wickes.co.uk/invt/420064

Most of the time the pipes will meet up on old & new, if not you can always
use flexibles http://www.wickes.co.uk/icat/cfflexible

Under a bath is usually more difficult because of the confined space.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257