Shower pressure problem?!

[eddyc2353]

Please help?! This has been going on since July 2012 last year!!
Had a new bathroom installed inc shower, bath, basin, toilet etc. the shower is a concealed shower valve with a large ceiling head shower.
It worked for a few weeks then there would be a short delay of water when the shower was turned and this got longer as time went on. Until nothing. I noticed that if you turned it to cold water came out but then I would add hot water and it would stop.
plumbing, gravity fed, 25 gallon header tank, shower cold has been taken off mains and hot from the cylinder. I have NO pump. Shower valve instructions state min 2.0 bar. The shower is on the ground floor, cold tank in loft and hot water cylinder on 1st floor.
work so far:
Valve was replaced suggestion of faulty non return Valve
Another new valve again
checked for air locks
you can sometimes get hot but most of the time no water comes out when on warm/hot temp. Cold always comes out when selected.
suggestions:
low pressure shower valve
single shower pump for hot supply to shower. Still be unbalanced as cold on mains so would you have to get a pressure reducing valve to control cold?
pipe in dedicated cold supply in for shower and fit 2.0bar pump.
But only got 35 gallon cold water tank? Will this run dry?
Unvented system ? This has been suggested because HOT WATER TAKES AGES to come out all over the house.
I know there has been plumbing downfalls, fitting a high pressure shower valve to a low pressure system, cold for shower taken from mains so we have an inbalance ... These are shocking errors in my opinion but we need a resolution.
Please help we are confused and desperate for the shower to work.
Thank you

 

[Howsie]

Get the people who installed it back. Total cock up from your description.

 

[Destroyer2813]

I would be thinking a bigger cold water tank with a pump and a dedicated cold supply from tank to pump, and get whoever installed it to sort itthey sshould of known it wouldn't work with unbalanced supplies

 

[PlumbBobBob]

as already stated get back whoever fitted it as the shower is not suitable for your system. i would say without measuring, that your hot water was at a maximum of 0.8 bar. the only way to get this working properly would be to get a pump fitted to the system with a larger cold tank (at least 50 gallons) as destroyer said.

 

[eddyc2353]

Get the people who installed it back. Total cock up from your description.

Yes needless to say we have been back, long story but they have been put to bed and we have a learnt a new lesson in life. I know they did the installation wrong but that is in the last. Future please!
thoughts on unvented system. Taking into consideration it takes ages and ages to get hot water in taps downstairs?!

 

[Destroyer2813]

Unvented is the best system for me, if you have sufficient incoming water pressure and flow

 

[Howsie]

Unvented.