Thermostatic Mixer Taps

Jeepers_Creepers

grumbler said:

AFAIK, unvented means that the hot water is under mains pressure. That said, I am not sure about the regulations for thermostatic valves in this case - I can imagine hot water sucked to the mains from a hot water tank.

Argh - I meant 'vented' - fed from a CWS in t'loft.

Soz.

Moss5

For the benefit of Grumbler, allow me to explain:-
Sink/basin mixer taps can tolerate unequal pressures because the hot/cold water streams only meet at the tap outlet. 
Each waterway is independent, until exit from the tap. 
Deck mixers bring the hot/cold together inside the body of the tap, it is important that they are equal pressures or the high-pressure cold will chase the low-pressure hot back to the hot tank. (non-return valves try to solve this).
Shower hoses are a single hose, if they were twin hoses, the two pressures could blend at the outlet shower rose. 
The solution is to provide a dedicated cold water supply from cold tank to bath mixer. Then you have both supplies at equal pressure.
This problem only exists where you have a vented hot water tank and a cold water storage tank in the roof.
Combi boiler owners have equal hot/cold pressures.

Norman_Castle

follows2006 said:

ic said:

Toolstation sell bath filler tap legs, that allow you to mount any wall mounted thermostatic mixer to your bath.  As we don't take baths only showers, I've swapped our bath taps for a thermostatic shower mixer.  It's a temporary job ahead of ripping out the bathroom when an extension is done in the near future.

https://www.toolstation.com/search?q=bath filler legs

Thank you all for the input, @ic didnt know about the tap legs and same dont really use the bath at all so this would be a great solution until we have a full refit next year.

The taps you've linked to include the legs. I fitted a similar one of these about 6 years ago and am still really pleased with it. I dogsat at a friends who had a non thermostatic mixer shower which drove me nuts trying to get the temperature right.

grumbler

Moss5 said:

This problem only exists where you have a vented hot water tank and a cold water storage tank in the roof.

Vented hot water tank - is it not a usual hot water cylinder fed from a tank in the loft?

If so, I don't see any problem

The solution is to provide a dedicated cold water supply from cold tank to bath mixer.

Why "dedicated"?

If a cylinder is connected to a tank, hot inlet of the mixer tap is connected to the cylinder and the cold inlet is connected to the tank, both pressures are the same, dedicated or not.

Moss5

The driving force for the hot water is the height of the cold tank. It would need to be 10-metres high to achieve 1-bar.
The cold water main is likely to be at greater pressure.
Providing a supply from the cold tank to the bath mixer would be a good idea.

grumbler

Moss5 said:

The driving force for the hot water is the height of the cold tank. It would need to be 10-metres high to achieve 1-bar.
The cold water main is likely to be at greater pressure.
Providing a supply from the cold tank to the bath mixer would be a good idea.

Why do you think it's mains cold water in the bath, not from the tank?!