Problem with cold water supply to shower

Postby markushaighus » Sat Jul 04, 2009 4:43 pm

Since moving into a 20 year old house last september, we found both showers to be faulty. The main issue being that the mixer shower temperature could not be altered. I have recently installed a new high pressure mixer shower in the ensuite as the system is using a combi boiler. The new shower has not made any difference and i have since discovered that I have a cold water tank in the loft. At first i thought this tank was redundant but have now found that the cold water supply to the shower is fed from this tank by gravity. Am I right in thinking that if the hot and cold pressures to the shower are NOT equal, then the shower will not work??? Shouldn't the shower be fed from the cold water main feed?
Any help would be appreciated.
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Simply Build It

Postby rosebery » Sun Jul 05, 2009 2:53 pm

You are correct you need balanced feeds. If the cold is gravity and the hot is at mains pressure then the hot will always overwhelm the cold. What slightly intrigues me is that you still have a CWST that feeds the shower when you have a combi boiler. Does it also feed bath and basin taps and loo?

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Postby markushaighus » Sun Jul 05, 2009 8:18 pm

the CWST must supply the bath as the cold tap on the bath doesn't work now the tank is empty. Not sure about the other taps though. Spoke to a plumber today who told me to redirect the shower pipe into the cold water mains supply to solve the problem. Thanks for the help.
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Postby plumbbob » Mon Jul 06, 2009 11:08 pm

It is normal as Rosebery says to remove the header tank when installing a combi. Maybe there is an obscure reason for this. Possibly the mains cold water pressure is so low it would take ages to fill a bath???

There are more showers on the market these days that have optional flow restrictors which the installer fits to balance unequal pressures between hot and cold. Normally, it has to balance high pressure cold and low pressure hot but I could see it working in reverse.

If you have good cold mains pressure, cut the header tank out but remember, if the toilet is fed from the tank, the ball valves will need replacing or modifying.
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Postby markushaighus » Tue Jul 07, 2009 6:02 pm

thanks for the help mate, yeah did the modification yesterday as i found that it was only the bath and the shower that were fed from the tank. The toilets were fed from the mains. There was another pipe coming from the bottom of the tank but have since found this capped off in the airing cupboard. Obviously this was used when the old hot water cylinder was present. I have now disconnected the tank and fed the shower and bath from the mains with expected positive results. I now have a shower that works!!!!! Looks like it was a bit of an oversight when the new combi was fitted. Not like it was difficult to do though. The people who had the house for 10 years before us must have had a low of very hots showers!!
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