Bath mixer tap issue

bazzabear · 17 Dec 2019 at 10:01

This is a slightly weird one.

We have a mixer tap on the bath in our (quite) new bathroom. If you run the hot water, it works fine. If you turn the mixer a little to add in some cold it is initially fine, but then goes to just cold water quite quickly. Turning the whole thing off when you realise this and restarting it turned all the way to hot - you still get freezing cold water.

I'm not quite sure what's happening. Is it that the cold feed is overpowering the hot to the extent that it's even forcing cold water back up the hot pipe?

Is this a known thing that can happen, and if so what's the fix? Some sort of non-return valve?

bazzabear · 17 Dec 2019 at 10:04

Forgot to say - Once this has happened, you can't get hot water back out of that tap for a few minutes (although that may be unfair - I've always only given it very short attempts, because it's making my bathwater cold!)

bremen1874 · 17 Dec 2019 at 10:07

How are the hot/cold water provided? Mains pressure, mavity, pumped?

if the cold is mains pressure and the hot mavity you can have problems.

Slade2 · 17 Dec 2019 at 10:16

If its a new bathroom you might find the tap has been fixed with a TMV. The TMV will be set to only get hot water out up to 42Degrees.

bazzabear · 17 Dec 2019 at 10:22

It is mavity fed hot. And I believe mains cold, I think the stored cold is only attached to the power showers.

bremen1874 · 17 Dec 2019 at 10:51

I'm not sure there is a good cheap fix for this.

Does it need to be a mixer tap?

Wayne666 · 17 Dec 2019 at 13:14

You can get taps which work with unbalanced pressures but it sounds like yours is not one of those. A non return valve will not work as the cold pressure will close the valve and you'll get no hot coming through anyway.

Option 1 - But a new tap.
Option 2 - Fill you bath with as much hot water as you need, then top up with as much cold water as it takes to get the bath temp to your liking.

Thebug · 17 Dec 2019 at 17:46

You could try turning down the cold side to balance them by closing the isolation valve slightly

R.C.Anderson · 17 Dec 2019 at 18:01

As others have said, it sounds like an issue with unbalanced water pressures, and a tap that can't handle it.

Easiest option would be a new tap, that can cater for the difference in pressures.

Another option (although I'm not sure if it'll work, but might give you something to look into), is a pump on the hot water to increase the pressure from the tank. I know you can do it with showers, for increased pressure & flow, so I don't really see why you couldn't do it for a bath mixer etc, but I've not looked into it, and I'm not an expert. (although if this did work, it might be able to increase the hot water pressure through the house)