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thermostatic mixer shower pressure

Postby jayrice72 » Sat Jun 23, 2012 11:57 am

I have had 2 different plumbers round and both have told me conflicting information.
Basically, we have installed a thermostatic mixer shower in the upstairs bathroom. We have mains cold water feed and hot water from a tank in the airing cupboard. The problem we are having is that the cold water pressure is much higher than the hot water pressure. As such the shower is running freezing cold and running a bath takes so long because we have to have the cold tap on low so we get enough hot running through, but of course this decreases the water flow and filling the bath takes for ever.
One plumber told us to fit a pump at the base of our hot water tank to increase the pressure, but the other plumber said this will make no difference and that basically we have the wrong type of plumbing for any shower other than an electric one.
We live in a council house and have been told that we will never be allowed to buy it. Hence, we do not want to spend lots of money on an electric shower plus the plumbing and electrician costs.
We are desperate- Does anyone have any kind of solution for this problem. Some sites have suggested fitting a pressure reduction valve to the cold pipe but I'm not convinced this will work either.
Please help!!!!
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Postby Barry Bunsen » Sun Jun 24, 2012 7:57 am

I think you have a few issues here.
Firstly I cannot see that the bath filling problem has anything to do with the shower. It seems your hot water flow rate is poor. If the hot water to the bath fills slower than it used to (or slower than your neighbours) there may be a blockage or air lock in the pipe or tap.
The thermostatic shower is working at unequal pressures (cold=mains/high : hot=gravity/low) and almost certainly wont function properly with this set up.
You cannot switch the hot to mains pressure without something like a combi boiler or unvented cylinder.
You can switch the cold to gravity pressure with more pipework from the loft but as your flow rate is poor I doubt it would help unless you then fit a pump. I cannot believe this would be a cheaper option than an electric shower.
In your position I would first try to find out what works for your neighbours as they should have a similar water pressure to you. Then I would investigate how to improve your hot water flow rate if it is possible. You will then be better informed to make a decision about your shower.
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Postby Perry525 » Mon Jun 25, 2012 7:15 pm

Replace the shower thermostat with a manual low pressure tap.
Lift the cold water tank in the loft as high as you can, to increase the pressure.
Take a direct feed from the hot water tank using 22mm dia pipe, bring this as close to the shower as you can, ditto for the feed from the cold tank.
This will solve your problem.
Do leave enough space round the cold tank to access the ball valve, should it need repair.
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Postby plumbbob » Sat Jun 30, 2012 11:24 pm

The problem with the shower is simple and I can't understand why your plumbers seem unable to offer a solution. I suggest you find someone who is experienced at plumbing!

Almost all mixer showers MUST have equal pressures on both hot and cold sides. You simply cannot use mains cold pressure on one side and low pressure hot fed from a header tank in the loft. If you want to see a diagram of how the plumbing should work, visit any shower mixer valve website and download any of the installation instructions.

in your system, both feeds should be low pressure. The hot feed should come from the top of the hot water cylinder and the cold should be from a dedicated connection to the header tank in the loft.

The temperature will then be even, but if you want to increase the flow from the shower head, fit a twin impeller pump that will boost both the hot and cold equally. UNDER NO CIRCUMSTANCES PUT A PUMP IN ONE FEED ONLY!

Hot and cold feeds must be fed from the same system ensuring the flow rates are always equal. This is to prevent a temperature fluctuation whilst the shower is in use which could result in a scolding accident.
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