I'm replacing the basin taps in the downstairs cloakroom with a single basin mixer, fed by mains pressure cold and hot from the hot water tank (unsealed system) so the pressures are quite different. I've noticed when looking through catalogues that some mixers have a low or high pressure option. Which type do I use in this situation ? couyal
It's very difficult to get a decent blended mix if the pressures are very different. At very least, you need a tap which feeds hot and cold separately right to the outlet nozzle - which almost certainly means that it will have separate hot and cold levers. If it mixes further back - as with a single lever tap - you stand a very good chance that the cold will force the hot back up into the header tank rather than coming out of the nozzle.
I haven't tried it, but I guess that you *could* use a low pressure mixer tap with a pressure reducer on the cold feed.
"Roger Mills" wrote
I have used a Hansgrohe single lever mixer in this application, which the suppliers claimed was suitable (thanks to the late Andy Hall for the recommendation). Fitted a non-return valve in the hot supply to avoid the back pressure situation. Removed the spring from the NRV though and installed it in the vertically upwards orientation (the spring causes a significant flow restriction).
Phil
How well did it blend hot and cold? The non-return valve would stop reverse hot flow,but it wouldn't necessarily prevent the high cold pressure from cutting off the hot flow.
There are thermostatic shower mixers designed for this -- designed specifically for multipoint or combi use. More specifically, they are designed for wide ranging hot pressure, varying in use, and very fast response. I fitted a Gainsburough one, and I was amazed at how well it worked -- whatever you did with the hot water pressure and temperature, it kept the output pretty constant, and shut it off completely if it couldn't (e.g. if you turned down the cold supply too far for it to mix in).
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