On 01/10/2012 18:26, MarkG wrote:
On Mon, 01 Oct 2012 17:49:25 +0100, Phil Addison
wrote:

On Mon, 01 Oct 2012 16:39:37 +0100, Roger Mills
wrote:

On 01/10/2012 10:00, MarkG wrote:


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....


Chances are that the combi needs to throttle the water going through it
in order to heat it sufficiently. [Otherwise you might have a very high
flow of luke warm water].

What flow rate do you get at (say) the kitchen hot tap? How does this
compare with the rate at the kitchen cold tap. If the cold rate is much
higher than the hot, throttle it so that they are more or less equal.
The shower mixer should then work better.

You seem to have been to posh bathroom supplier, at least by the look
of their website.
Would it not be their responsibility to have installed a shower
suitable for your
pre-existing boiler?

--
Phil Addison


Well it's suitable for both hi and low pressure systems, but clearly can
get freaked out by large differentials in pressure. They didn't
install it, they just supplied the valve, and it's not even theirs, it's
a stock concealed thermostatic triple valve that every man and his dog
seems to use these days, they just do their own knobs and faceplates to
suit...


Been on a trip to Plumbase and picked up a 15mm pressure reducing valve
on the cold side.

http://www.ebay.co.uk/itm/Honeywell-...item3ccade1b3c


or a check valve on the hot side to stop the cold going back down.

http://www.ebay.co.uk/itm/BRASS-SING...item3a5e3438e2


Not sure what's going to be best (opinions???), but have both options
available.. The other option I have considered is that my boiler might
not be pressursing the hot side correctly, and it's only become a
problem now, so I guess I need to pressure check both sides to see what
I have...

You want to use the non return valve on both hot sides!

What is happening is this...

Your shower comprises of a mixer then a simple on/off valve, so when the
valve is off, this is just stopping the mixed water from exiting through
the shower head, it should already have a check valve, the PDF you
linked to shows it does, but this doesn't seem to be working, or the
shower only has one on the cold, or it has one on the hot, but has been
connected the wrong way around (do you get hot water out the shower when
you ask it to deliver hot!?)

Fitting a non return valve to the hot feed to the shower will prevent
cold water passing through the valve when you open a hot tap, and the
boiler restricts the flow to get the temperature you have asked of it,
if the boiler didn't restrict the flow, then too much water would pass,
and the boiler would not be able to raise the temperature enough, so
when the boiler is restricting the flow, water then passes through the
shower mixer, as it is an easier path.

If you are just taking cold water at a high rate (bath tap, or multiple
taps open on cold possibly), then I expect you may end up with water
flowing the other way through the shower valve, this is why I suggested
having two non-return valves on the shower, one on each feed.

--
Toby...
Remove pants to reply