Firstly, I should caution that I have no clue about plumbing, as will become immediately apparent. Not planning on doing any work myself, just trying to understand what work needs doing...
I recently had a new bathroom and shower installed in my house (c. 1980 build) and I had mistakenly selected a thermostatic shower fitting that requires 0.5 bar of pressure.
This is an integrated thermostatic mixer, not just for the shower but bath taps as well.
Ebay item number:16109524945
It is usable, but the pressure is not brilliant. This is because there is not pressure on the hot water circuit. More likely to be 0.1 bar.
It appears to be gravity fed, so there is a cold water tank in the loft, a modern condensing boiler in the kitchen and a hot water tank and central heating pump in the airing cupboard on the first floor.
Pressure on both hot and cold to the bath\shower is not brilliant. My understanding is the pipework is 22mm feeding into a 15mm fitting. No idea whether this is standard.
The shower pumps I have seen appear to sense when water is flowing and then kick in. By the sounds of it, I need a twin impeller one because both hot and cold are low pressure (I checked the flow rate).
What I am confused about is, in the bathroom, where does the sink get its water supply from? If I follow convention and site the new shower pump in the airing cupboard, does that imply I will be increasing the pressure to the sink taps as well (which I don't want to do).
The alternative would be to site the pump under the bath, which is logistically achievable, but not particularly advisable as the pump needs some ventilation, or so I have read
However, if I don't site to there I am concerned I will be increasing the flow to the sink as well.
Is it normal for shower\bath and sink water supplies to come off the same pipe?
The other query I have is, how do I rig up the pump to the hot water tank. From what I can see, you use an Deleted or surrey flange and site the pump below the level of the tank.
But the hot water tank already has three pipes going in\out of it, cold seems to come in the top, presumably from the roof tank.
Then there is a tangled quagmire of pipework which appears to be associated with the central heating pump.
If anybody can shed some light on this I would greatly appreciate it...
Hi Nick The normal method for a power shower, is to connect the hot directly to the cylinder as you describe, with a surrey, or Deleted flange. Then a separate cold supply is taken from the storage tank to the twin impeller pump. The only device served by the pump would then be the shower. In your case, shower being bath tap. the basin would remain connected to the existing supplies. The airing cupboard would be the preferred site for a pump, but under a bath is possible. If going under the bath, I would strongly advise to get the advice of an electrician first, to ensure safety, and to comply with regulations, don't just a plumber with the electrical supply.
As this is not going to be a cheap project, and some find the noise from a pump a problem, could there not be another way round the problem. Raising the storage tank on staging in the loft would increase pressure. or perhaps that mixer might just have to be replaced.
I will look into raising the height of the cold water tank as well.
Siting wise for a pump I am coming to the conclusion the airing cupboard is more suitable.
Pump Wise. Looking at a reconditioned stuart turner monsoon twin. Equivalent price to a new cheaper pump, but has the look and reputation of being built to last.
Why is a separate cold water draw required from the cold tank? At least 25mm below any existing draw as far as I can see, presumably this is to prevent the pump running dry if other taps\faucets are turned on in the house, much like the surrey flange for the hot feede.
I have a Stewart Turner at home, it serves two showers, and must now be about 20 plus years old. although I couldn't comment on a recon version. You must provide entirely separate hot and cold supplies to the pump in usually 22mm. Reasons as you say plus prevention of scalding, should another cold tap be opened.