Increase water pressure to shower pump?

Hi everyone, I have used these forums a lot to help me over the years but this is my first post.
I have recently removed my electric shower and fitted a mixer shower with shower pump (salamander CT75). It has a direct feed from my cold water tank and the hot water cylinder as instructed. The problem is there is not enough pressure to keep the pump running constantly. Turning the shower to full cold or full hot makes the pump run fine but at my preferred temp it cuts on and off all the time. With the pump switched off the water only just dribbles out the shower head. If I disconnect the outlet pipes from the pump it flows through the pump quite fast though. I think the problem is the height of the shower head compared to the water tank (shower head is directly below the tank). Anyway it is only a 25l tank in the loft and due to the shallow pitch of my roof it cannot be mounted any higher. My question is would adding a 2nd 25l water tank beside the existing one increase the pressure or is there any other way to do this?

The pressure switches which turn on the pump aren’t activating correctly; ideally you need 600mm or more from the tank to the shower head or you could potentially be in a negative head situation but in some cases you can get away with just 200mm. Did you use the old shower pipe work or run new & what size is it? Can you explain a little more (or better still sketch/photo) where the pump, pipes & shower head are located.

Minimum recommended capacity for a power pump system is 250 litre per bathroom. I find it difficult to believe you have only a 25 litre cws tank , it sounds like a central heating header tank; are you sure that’s correct? If it is you will have to restrict yourself to very short showers!

I had a similar problem and a pair of RCM3's sorted it:- (scroll down page)

http://www.h-i-e.co.uk/acatalog/Right_RSP_Pumps.html
[/url]

Thanks for the advice, I think my best option would be to fit a new pump that works for negative head systems. Can anybody recomemd one that will suit my needs. Needs to pump both hot and cold feeds and I would like a similar bar rating to my existing (2.1 bar).
Thanks

Why not fit the RCM negative head unit Boxerman recommends, it will turn your existing positive head pump to negative head, if that is indeed your problem. Salamander also make a self selecting unit ESP 75 which is 2.5 Bar but, remember, even a negative head pump must still be mounted below the CWS tank.

Are you sure that’s your problem; you didn’t say weather or not the pipe work is new? & whatever pump you fit it won’t work effectively if the CWS tank is of insufficient capacity; you didn’t say if the previous 25l figure you quoted was in fact correct? If it is, the system will never work.