Shower pump for low pressure hot water

Postby pete34 » Fri Jan 30, 2009 11:55 am

Hi, I need advice.
Having fitted a new bath and basin I now have low pressure/flow in the hot tap basin.
Also, the bath taps are a shower mixer and as the cold water is mains fed the water will not mix in the shower (at shower height).

Would it work if I fitted a pump, say 1.5 bar to the hot water pipe before both bath and basin and a non return/ double check valve after the pump and a pressure reducing valve to the cold feed?
I phoned a really unhelpful plumber who told me I had the wrong taps and didn't know what I was doing!

Thank you for any help
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Simply Build It

Postby stoneyboy » Sat Jan 31, 2009 5:51 pm

You will need to determine the mains pressure at the usage point and buy a single impeller pump which gives a similar output presssure. The NRV will need to be fitted in the mains pipe.
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Postby pete34 » Sun Feb 01, 2009 6:46 pm

Cheers Stoneyboy,

Thanks for your help.

I spoke to salamander 'pumpwise' but they recommended a pump that costs about £300!
By fitting a 1.5 single pump and reducing the mains pressure, if need be, I was hoping it would even out the pressures at the taps. Then I could fit an NRV to both to prevent cold flowing back into the pump or hot to the cold.

I could do this for about £120...

Any reason why it wouldn'y work?

Thanks, pete
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Postby stoneyboy » Mon Feb 02, 2009 6:00 pm

You may get a pump for £120 but you need to add about £40 for a proper pressure reducer with gauge (careful you don't get fobbed off with a flow reducer).
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Postby plumbbob » Mon Feb 02, 2009 11:22 pm

You may still have problems even with the expensive pump because as the feeds are from different supplies, it is going to be almost impossible to balance them exactly.

Frankly, if you are going to try something, spend as little as possible (a 1.5 bar) and do as Stoneyboy suggests. It may work, but maybe not. Can't say, as it is not a standard installation.
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Postby rosebery » Tue Feb 03, 2009 12:57 pm

Whilst it sounds as if the plumber you consulted was less than sympathetic I'm afraid he's probably correct. I'll bet you have 1/4 turn ceramic disc taps and the basin is a monobloc (with those dreadful 7mm restricted tails). Your restrictions on the BSM is discs plus tails plus the diverter.

If you used standard isolating valves to comply with water regs these are also restrictive and should be full bore. I'm presuming you also fitted a non return vv on the BSM hose if it didn't come with one which is also restrictive.

The main problem is not pressure its flow rate with the restrictions imposed as above.

There is, however, a possibility of a pressure problem if you've used those nice up and over U shaped taps which do affect pressure because of reduced static head.

I'd suggest you run a cold feed from the CWST (so both hot and cold will be at same pressure) use a pump and pump BOTH hot and cold because as already mentioned it will be virtually impossible to get them balanced properly with pumped hot and mains cold. Even if you do achieve it then all the water board has to do is change the mains pressure even slightly and they'll be unbalanced again.

If you don't fancy that little lot then perhaps you should look at changing the taps.

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