Bath Mixer Tap with Shower - different pressures

[StephenW]

Just fitted a bath mixer tap with shower attachment. It is a Bristan tap and says it's suitable for all pressures. However, I have mains cold and low pressure hot. This works fine for the tap but when diverted to shower the cold water overpowers the hot and starts to force it back down the supply pipe (the pipe goes cold). Both are supplied at 22mm although the cold starts off at 15mm and becomes 22mm from a tee-piece feeding the cold water tank in the loft.
I have the cold feed turned down at the isolator but can't turn it any lower and still have adequate flow to the bath.
Do I need a one-way valve in the hot supply to stop the cold forcing it back? If so, what specification do I need? I know pumping the hot would probably answer the problem but that will have to be a longer-term solution. Thanks.

 

[muggles]

It'll say somewhere in the installation instructions that the pressures should be roughly equal. Although the tap is suitable for all pressures it is not suitable for very unbalanced pressures. You could try a check valve on the hot (I do hope you've fitted one on the cold...) but I doubt it'll ever work properly

 

[Goldspoon]

A similar thread running now:

//www.diynot.com/forums/viewtopic.php?t=200084&postdays=0&postorder=asc&start=0

 

[StephenW]

Chewing it over I realise that a non-return valve in the hot might stop the cold from filling it but that the hot pressure (or lack of) will still mean that the hot can't get through. So, is pumping the hot (it comes from a hot water cylinder) the answer? If so, what pump would be most suitable?

 

[muggles]

You could pump the hot but you'll need to get a pump that's matched to your mains pressure otherwise you'll still get problems to some extent. The other option is to pump both hot and cold.

Salamander, Stuart Turner and Smedegaard are all good pump manufacturers

 

[Goldspoon]

Take your cold supply from the cold water supply tank?

 

[StephenW]

I've about reached the conclusion that an electric shower with the mains cold feed will be the best bet and probably come to about £200 with the cost of electrical bits as well (qualified electrician comes free!). Any other methods (pumped hot or pumped hot and cold) would probably cost as much, be more hassle and may still not provide the ideal solution. Thanks for your help in this and the other related threads.

 

[kevplumb]

Any other methods (pumped hot or pumped hot and cold) would probably cost as much, be more hassle and may still not provide the ideal solution.

better than any electric shower