Mains supply to mixer tap is pushing cold water to hot water pipe

[LordWest]

I live in an apartment block where generally hot water is supplied from the communal hot water cylinder and cold water to bathrooms is supplied from cold water tanks in the loft. It is a vented system. However, in a basement flat and a ground floor flat cold water supply to bathrooms is through the mains (as in the kitchen of course). Because the pressure from the mains is much higher than for the hot water supply, in some mixer tap the mains water in the mixer tap pushes mains water through the hot water supply into the communal hot water cylinder and then hot water rises into the cold water tank in the loft creating an overflow....

What issues should we be looking at the mixer taps for this problem? We have not identified the mixer tap yet.

Many thanks,

 

[Ben-gee]

Put a non return valve on the hot supply to each mixer tap that has mains fed cold.
This should be done on all such installations.

 

[LordWest]

Put a non return valve on the hot supply to each mixer tap that has mains fed cold.
This should be done on all such installations.

Thanks. Does this problem arise when one is using a mixer tap, or can it happen when the mixer tap is turned off? Does it usually happen because the mixer tap is faulty, faulty designed, or something else?

 

[Ben-gee]

It can even happen when off, depends on where the hot/cold shut offs are relative to the mixing chamber part of the tap.

When I am replacing kitchen taps with this set up I go for a dual flow spout, this is where no mixing occurs within the tap body - the streams just mix as they exit the spout.
This design will give you no problems when you have unequal supply pressures - it does limit design choice but there you go.

 

[LordWest]

It can even happen when off, depends on where the hot/cold shut offs are relative to the mixing chamber part of the tap.

When I am replacing kitchen taps with this set up I go for a dual flow spout, this is where no mixing occurs within the tap body - the streams just mix as they exit the spout.
This design will give you no problems when you have unequal supply pressures - it does limit design choice but there you go.

Thanks.