Following on from my request for info on shower pumps, I have now spoken to a neighbour who advises me she has had a shower system installed which relies on mains presure to give a strong shower.She gave me some leaflets which show she has a TREVI boost. Because she is recently widdowed, I don't want to trouble her any further .To me it seems too good to be true (no pump, no essex flange , easier plumbing).
Has anybody had experience of such showers?

I had a look at their web site and it appears to use the power of a (new) mains pressure cold pipe to boost the flow rate of the (tank pressure) hot supply.

http://www.trevishowers.co.uk/builtin_valves/boost_a.html

Looks like you would need to run a new pipe from the mains pressure input to the house to the shower. That might be harder than inserting a pump in the existing pipe and running a new pipe back to the tank. All depends on the layout.

I've only fitted one of them and wouldn't do it again. The temp was not that good and the only way to get it higher was to turn up the cylinder to over 65Deg. Pressure/flow wasn't that good either, mains was about 3bar.

Not had any problems with other Trevi mixers, fitted loads of Therms.

Jason