Poor hot water flow on new mixer tap

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brassmonkey | 19:53 Wed 29th Nov 2006 | DIY
5 Answers
I've just upgraded to a fancy new mixer tap with a pull-out showerhead for the kitchen. I always had slightly low hot water pressure in the kitchen, but now it is at a point where I barely get a trickle. If I run the cold water only, it pushes the hot water back up the pipe. If I use the shower attachment, the hot water flow is twice as good!

If I swap the hot and cold connections round, it doesn't help. I've checked for airlocks and cannot find anything obviously wrong with the tap itself. I'm pretty sure that the design of the tap itself is no good for my hot water pressure, but it was a Fleabay item bought some time ago, so I can't take it back. Anyhow, I love the design and the missus is really keen on the shower bit!

My question is, can I buy some kind of small shower pump or a Grundfos underneath the sink to boost the pressure to the hot side? I don't want to shell out on a big pump for the whole system for the sake of one tap - the rest of the house is OK. Do I need to fit non-return valves on the inlet pipes if I do this? Or am I just better off giving it up as a bad lot and buying a different tap? I'd still have rather low pressure with a new tap, but it would probably be passable.


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Hi Brassmonkey,

Do you live in a Bungalow?

A small single pump should do the trick. You also need double check valves fitted and isolation valves fitted aswell regardless if you have a pump or not. You may if you have one that is; move the header tank higher up to get more head ( pressure) if this is practical.
Also If you have just fitted this tap your self you have to get the local council to come out and check it is installed to regulations , And seems as though it is a mixer tap and you havent allowed for any backflow protection then you have just breeched regs and it will be condemed you may even be pollouting the local drinking water, and be in serious trouble. All plumbing, ventilation and gas works have to be carried out by a competent person or passed by a building inspector in the case of water if you DIY.
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I don't live a bungalow, the header tank is in the loft. I have isolation valves and will fit check valves ASAP.
It could be the problem is the tap itself. Many European taps these days are designed to work at about 1 bar pressure from both the hot and cold supply. Where you have an unvented system like a combi boiler, hot and cold are at mains pressure, so this is not such a problem. But if you have a gravity feed hot-water tank, there may not be enough pressure for the type of tap.
As gasman says, this can cause problems with backflow in mixer taps between cold and hot pipes, and, yes, there are regulations about this. Fitting a pump alone can just increase the backflow problem. It's not like the old days. You have my sympathy!
Heatfield is correct I suspect. Most taps are now issued with the following abbreviations:
LP - low pressure
HP - high pressure
AP - all pressures
The problem is the people who sell them are either not properly trained or couldn't care less as long as they get a sale.

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