Additional Cold Water tank to increase hot water flow.

[lidster]

Hi All,
Ive got a vented gravity system. 50 gal cold tank in the loft. bought a new mixer tap for the bathroom sink which is on mains cold, but the hot water is from my tank.
https://www.screwfix.com/p/bristan-blitz-basin-mono-mixer-tap-with-clicker-waste/410gf

Flow through the hot side is terrible. a trickle, despite it being suitable for gravity fed systems in the screwfix description. Ive noted that it needs 0.2 bar pressure. I have exactly 2 metres of head to this tap outlet.... possibly im out by 10cm.... the cold feed into the bottom of the hot water tank is 2.6 metres. It needs a non return valve adding - the cold is pushing the hot back into the tank - its all isolated at the moment - just using the coldfor now.

I am going to replace the isolation valve just under the sink to a full bore one.
I have also bought a non return valve for the hot but cant see any full bore ones....

My question is - will the full bore fittings make much difference? The flexy hoses provided into the tap are reducing the pipe diameter anyway.

Ive also read that flow is increased if I join another Cold Water Tank in the loft - so that a greater body of water is pushing down the pipe. This seems to be debated a lot with most people saying its only the height that matters....

Any help /advice please?

 

[bernardgreen]

This seems to be debated a lot with most people saying its only the height that matters....

It is only the height that matters as regards the pressure ( aka head ). From surface of the water in the tank down to the tap.

 

[Madrab]

Water pressure in a gravity fed system is dictated purely by height above a given outlet, hence the saying - meters or ft of head of water.

Your issue is that you are using mains cold water and gravity hot water and the higher cold mains pressure is restricting the hot water pressure in the body of the tap. Unless you equalise the hot water pressure with the cold you will continue to have issues with a single flow tap, regardless of what you add to the system.

You need a dual flow tap or pump the hot.

 

[JohnD]

or run a new cold water pipe to the bathroom from the loft tank.

It will be less noisy, and will enable your mixer taps to work, and will remove the risk of cold pushing into the hot cylinder and causing the loft tank to overflow.

 

[polesapart]

You can get copper tails to replace the narrow-bore hoses e.g.

https://www.wolseley.co.uk/product/bristan-copper-tails-12-x-265mm/

But mono-cartridge mixers like yours don't like unbalanced supply pressures