Shower - high pressure when on cool, low pressure when hot?

The pressure will drop as you turn the temp control up.

The shower will slow the flow rate so that the water running past the heating elements is heating it up enough for you.

So, the colder you have it, the less the shower needs to heat it so will run it through quicker. The hotter you need it, the more time it needs to flow over the elements to heat the water up and it will slow the water down.

You will notice a drop in pressure as you turn up the heat - this is normal. If it's not a pumped shower it can sometimes slow the water down a little too much to make it an effective shower.

Spanner Man
October 2008

This isn't really likely in the most of the UK but I lived in a remote area on a group water scheme in another country until a couple of years ago and our shower used to loose pressure when running on hot.
First of all it was fed from a tank in the loft so make sure that your tank is filling properly if this is the same setup for you. then my problem was that the filter was getting blocked up with silt and weed as we got our water from a lake and it wasn't filtered.
As I say not likely with Thames water or the like but keep it in mind. If it is doing this then the temp will rise compared to where you have set the knob over a period of time, so you will find its hotter at a lower setting but less water flow. our man Rich above is likely to have the more likely answer though.
Another possibility in hard water areas is that its just scaled up. This will mean it takes longer to reach temperature and the controls will slow the water down until it reaches the required temp.
If this is the case and you really feel like messing about for an afternoon ( wet, nothing on telly, all pubs in the country on strike, missus giving you funny looks) you could remove the wee boiler and try to descale it either with the citrus acid descaler you get in the shops or with a strong mix of lemon juice and vinegar but FLUSH IT OUT AFTERWARDS. Like I say really messy.
Good luck

Kenny F
October 2008

But it was a fine a couple of years ago, winter or summer!?

Mark
October 2008

Dead easy,no problem with your shower at all,the water in the reservoir is 'bo@@ick'ar@e'freezing at the moment and your shower can't run at full pelt and heat the water up as it did a month ago.The shower power determines the heat+force,run it slow=hot water run it fast=cooler water,look at showers in DIY stores(B&Q-Wickes etc)1000kw shower or under about £90 quid or so,then the price jumps ?£250 upward!If you want lots of heat and power you will have to upgrade mate!

Rich
October 2008