Shower mixer tap fitting

31 Mar 2012
Reaction score
United Kingdom
I am considering replacing a failed electric shower with a set of bath taps with integral shower head. Cold water is off the mains and hot is from a vokera combi boiler. Hot feed to tap is 22mm fitted with a flexible pipe and cold is 15mm, also with a flexible pipe. If I fit the new tap/shower mixer to the bath and the existing pipes will there be any risk that the restriction of the shower head will cause the cold water to enter the hot line and flow back to the boiler. Would it be necessarry or advisable to fit non return valve to the tap inlets. Sorry if this is a dumb question.
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As the shower head can enter the bath water, as far as I know you need check valves.

To stop the potential of dirty bath water entering the mains cold supply via the shower head.
I intend to fix the head to the wall to be used as an over the bath shower so the head should not come into contact with the bath water. My concern is whether the shower head would cause back pressure in the hot sysytem.
I'm sure the shower head could still be left in the bath, so I think my point still stands.

As you are on a combi, it's mains pressure on both.
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Thanks Paul, I appreciate I will have to fit a check on the cold as understand this is a legal requirement, correct me if I am wrong, I was unsure whether one was needed on the hot as well.
I would assume the combi will have a check valve built in for the hot, but you may have to wait for more responses on that.

Cold, yes.

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