I recently purchased and installed a tap (pics below). I found that if I keep the main tap handle open but keep the outlets closed, I hear hiss sound of the water as if the water is still running. I ignored this and then water started overflowing from an overhead tank in the attic.

A handy-man told me that the tap hasn't got a non-return valve. I should put a NRV. Is he correct? Can I add an NRV to the existing pipework? Have I bought a wrong type of tap?

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  • When you say "main tap handle", are you referring to the squeeze lever at the end of the sprung hose or are you talking about the temperature/control lever at the fixed base, just above the sink? Which "outlets" are you keeping closed?
    – FreeMan
    Jan 4, 2022 at 12:25
  • main handle = mixer lever on the left Jan 4, 2022 at 14:52

1 Answer 1


The cold supply has a higher pressure than the hot which is fed from the tank in the attic.

So you need to fit a not return valve in the hot supply to the tap shown and make sure it is fitted so flow is from the pipe to the tap.

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