Is this (easily) fixable


My in laws have a mixer shower that me and he fitted a few years ago. Their system then was a gravity fed solid fuel system, with a copper cylinder and a massive cold water header tank in the loft. The shower was fed from these two tanks. They have now had the system changed to a gas combi boiler and all is fed at mains pressure, the main reason for the change is they are getting on a bit and the thought of having to go for the fuel at the bottom of the garden started to look less appealing!
The problem is if anybody flushes a toilet, turns a cold tap on etc. when the shower is in use it gets a bit hotter due to the 'now shared' cold water pressure. It doesn't get hot enough to scald so isn't a major rproblem but if it can be quite easily and quickly remedied the FIL would like to do it. Due to him being nearly 70 and the bathroom looking really nice with flush fitting shower valve and head, replacing it with a thermostitic mixer is NOT an option.
Any ideas / thoughts most welcome.
Cheers
John
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Replacing it with a thermostitic mixer suitable for combi/multipoint is probably the only thing which will give a satisfactory fix. The combi installer should have warned you about this as it's entirely predictable. (I wonder if they checked the mains pressure and flow rate was suitable for a combi?)
Other things you might try... Reduce the flow to the toilet cistern so it makes less impact on the water pressure, at the expense of taking longer to fill. If it's got an isolating valve, you could try half closing it. You could try the same for other water consuming items. If your mains water pressure is reasonably high, you could fit a pressure reducing valve on the shower cold water supply, so it doesn't see pressure fluctuations, providing the supply pressure doesn't drop below the pressure reducing valve set pressure.
--
Andrew Gabriel

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John wrote:

IANA plumber but did see something in the Screwfix catalogue that might help:
You can get inline thermostatic mixing valves, that you could connect into the existing hot water supply going to the shower, plus a connection to the cold water supply.
http://www.screwfix.com/app/sfd/cat/pro.jsp?id 024&ts0564
That will limit the hot water temperature available at the shower.
Whether you would be allowed to use one on this system, is a different matter.
--
Sue

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If you have access to the water pipes try fitting this in place. http://www.plumbworld.co.uk/344-0000
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In an earlier contribution to this discussion,

It might help.
What worries me a bit is that a sudden demand for water from - say - a cistern will reduce *both* the cold and the hot flow. So even if you balance the pressures, the reduced flow through the combi may result in a higher outlet temperature - so the mixed temperature will *still* rise.
--
Cheers,
Roger
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Think you're right Rog, bugger.
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fred
Plusnet - I hope you like vanilla
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I agree - reducing the flow will result in higher temps. In the depth of winter I find that flushing the toilet will give a warmer shower for a few minutes!
John
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wrote:

I'm not quite sure how to picture that.. ;-)
Prob. best not to..

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Opening the main stop cock a bit may reduce the effect as may closing down the toilet cistern inlet but are unlikely to totally cure the problem.
Using a pressure balancing valve may work better than a pure (wax capsule) thermostatic valve as it will respond more quickly to a step change in pressure.
See: http://www.plumbingpages.com/featurepages/Greens.cfm for a case study almost exactly matching your situation but it's 40 quid for the parts alone: http://www.plumbworld.co.uk/344-0000 or a bit cheaper here: http://www.bes.ltd.uk/products/110.asp (this price + vat & post).
--
fred
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