On 01/10/2012 10:00, MarkG wrote:
Hi, have a Worcester 35CDi II combi, and everything was fine until
plumbed up shower mixer valve. Now, whilst the heating works fine, the
hot water only cycles between lukewarm and cold (with the boiler
switching the heating off soon after it goes on).

Now there was some vague blurb in the mixer tap fitting instructions
about the water pressures. We have very high water pressure here
~5Bar, and I a quick Google has brought up a single mention of someone
seeing something similar, that the pressure of the cold water is going
through the valve and back down the hot output.

Can someone elaborate on this? What are my options on how to fix this?
Fit a pressure reducer to the cold feed? What sort of pressure will my
combi hot side have? I always thought it was the same as the mains
pressure when you had a combi....


Mixer PDF:
http://www.roperrhodes.co.uk/wp-cont...TRUCTIONS7.pdf


"Unbalanced Water Supply
Valves must always be operated within either the range for BS 1287 OR
BS1111 as described in the table below. Valves cannot operate
effectively where a hot or cold pressure system crosses the boundaries
of the two ranges. In addition the maximum ratio of unbalanced hot and
cold water pressures for the valves to operate effectively is 5:1. Hot
or cold pressure must be reduced or boosted so as to work within the
required range.

Maximum Water Pressure
Concealed Dual and Triple Control shower valves are suitable for use
with all water supply systems up to a maximum of 5.0 Bar. Operating
pressures above 5.0 Bar will require the installation of pressure
reducing valves."


Can you isolate the hot or cold to the shower mixer valve?
If so, do that (either of them or both) and if that solves the problem,
simply fit two non return valves to the hot and cold feed to the mixer.

If you cant isolate the shower, put the mixer to coldest setting and see
if that solves it, if so, fit the non return valves.

--
Toby...
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