Single Impeller Pump on Cold Tank

[Danny Monaghan]

Our heating and hot water run off a solid fuel Rayburn, which gives us an enormous amount of very, very hot water. I've just fitted a shower running off the hot cylinder and cold header tank (which is approx 10' up from the shower in the loft). The shower is a simple thermostatic mixer valve with an 8" soaker head on it, but the flow is a little disappointing and you have to have the mixer turned practically all the way to cold to get it cool enough to use. By way of comparison, we have a shower hose on the bath taps which runs off the rising cold main and you get good pressure and mix through this - it's just not safe if someone else turns a cold tap on.

I was planning on boosting the shower's cold supply by using a single impeller pump mounted by the tank in the loft so the cold has a lot more pressure. The reason for only pumping the cold is I've been told that the hot water from a Rayburn ruins pumps very quickly because of the temperature, and also it would balance up the mix at the shower because there would be more cold coming through.

Am I on the right track here and does anyone have a recommendation for a pump and the size that is likely to be best?

Cheers

[Bob Minchin]

I wonder if you might be better off with a larger bore cold feed to the shower so the mixer working point is more in the middle of its range. Also the position of the control on your mixer should be purely a function of the output water temperature and not needing to be set as you suggest. It would appear that the thermostatic bit is not controlling the temperature. Or may you could consider reducing the temperature of your general hot water supply. I'm not suggesting going down the route of the recent 'nanny state' thread but it does sound like there are some safety issues with your very hot water supply. just my 2p

Bob

[Dave Liquorice]

I assuming that the HW system is the normal open vented type.

What size pipe did you use to bring the cold water down to the shower mixer? I suspect the HW feed and distribution will be 22mm, the cold feed to the shower also needs to be 22mm and from the same header tank, not the one for the primary circuit... (I think you would have noticed if you'd done that though). The available flow and pressures at the shower mixer need to be fairly closely matched.

[Doctor Drivel]

From the cold tank run a dedicated 22mm pipe to the cold on the shower mixer.