Combi boiler: shower pressure too high

[apjilly]

We recently had a Bosch combi bolier installed and a new Mira Discovery shower (because the old Mira wouldn't work without a gravity feed, and the tanks above the shower were taken out with the old boiler).

We tried the shower and it seemed to have a mind of its own (even when no other appliances were in use), adjusting from hot to cold, and from a trickle to full blast. Our installer told us the reason was that the Mira Discovery (which they selected and supplied), when used with a combi bolier, must have the shower pressure set to full or the boiler will get confused and will cut the supply. Apparently at lower pressure settings the water spends too long in the boiler, gets too hot and then cuts off - surely the boiler should regulate this?

At full blast the pressure is so high it hurts - it feels like you have pins and needles.

We can't find the 'Eco' setting on the showerhead (which should be there according to the instruction book) so we have no way of reducing the pressure without the boiler cutting the entire water supply. I'm dubious that this showerhead setting would solve the problem sufficiently anyway.

It seems the shower and boiler are incompatible. We were told before the work started that the temperature and pressure would both be adjustable, but they aren't. We've been offered the money back for the shower (which was supposedly a freebie) but from what they've said a replacement won't be any different. It sounds to me like only an electric shower or a different boiler (like our old one, complete with hot tank) would enable us to have adjustable heat and pressure.

Can you tell me if what the installer says is true, and recommend anything we could try?
Cheers

[ChrisR]

WOuld be surprised if Mira and Bosch don't work together.
Has the shower hose got twisted inside?
Suppose you turn the temp down on the boiler?
It could be the boiler isn't cutting heat down ("modulating") properly.

And I'd call Mira technical.