Kitchen Mixer Tap - Urgent help required please

[alfazzr]

New on here, but hoping for some quick assistance. Has anyone plumbed in a kitchen mixer tap with spray head attachment. You know the type, singe hole stainless steel 11/2 bowl sink and ss tap, single lever mixer art base rising up to a horizontal swivel 'neck' for the main tap (with second on/off 90 degree tap at the end) and an outlet for the main tap.

Rising up above the main horizontal outlet is the attachment to a flexible hose in a large coil spring leading to a spray outlet which resides in a swivel holding arm projecting from the main body.

OK, I plumbed it in yesterday replacing an older leaking swan neck two valve mixer. I had isolation valves under the sink but instead of the previous soft copper tails this one has long flexible braided connectors so I used adapters after the isolators for go from 15mm copper to a half inch bsp screw to fix the flexibles to.

On refilling the system the cold works fine. The hot has vey little flow. I can only think that I have possible restricted it with some stray ptfe tape OR something else in the tap is introducing additional resistance on the hot side. (Mine is a hot cylinder with loft header tank system).

Now, when I put the main valve to mix flows and close the outlet at the end of the horizontal arm (ready to use the spray head) I can hear the cold flowing back up my hot pipes and if left on would eventually overflow the header in the loft I guess. Although it is less noticeable I think I get the same effect when just using the mixer tap normally (ie cold flowing back up the hot side).

What is normally there to stop this happening? I can imagine a non return valve on the hot side would possibly cure it but this is surely not an essential but unmentioned part of the installation.

Any helpful thoughts gratefully received.

[alfazzr]

Do these taps come in types for combi's only by any chance - it was not marked as such but that might explain it if they required equal pressure on hot and cold sides ? (I do hope not).

[htg engineer]

You need to check the taps instructions and/or with the manufacturer/supplier. The tap could be meant for use on mains pressure systems not tank fed.

[stoneyboy]

alfazzr,
Unfortunately you have a tap intended for a combi boiler.
Fitting a non return valve in the hot feed will further restrict the hot flow.
You have two choices: fit a pump in the hot water supply or scrap the tap and replace it with one for low pressure. Be wary of claims that taps are suitable for low pressure - even some of the ones claiming this do work but take forever to fill a bowl with hot water.
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