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Problems with hot water since fitting shower mixer valve.
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MarkG
Oct 1, 2012, 5:00:47 AM10/1/12
to
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-content/uploads/2012/02/DUAL_TRIPLE-INLINE-SHOWER-VALVE-INSTRUCTIONS7.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."
--
Using Opera's revolutionary email client: http://www.opera.com/mail/
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-content/uploads/2012/02/DUAL_TRIPLE-INLINE-SHOWER-VALVE-INSTRUCTIONS7.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."
--
Using Opera's revolutionary email client: http://www.opera.com/mail/
Toby
Oct 1, 2012, 7:19:11 AM10/1/12
to
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...
Remove pants to reply
MarkG
Oct 1, 2012, 10:15:30 AM10/1/12
to
up for a while, he only turned the isolators on last night, which was
exactly the time the other problem cropped up, so pretty sure it's related.
Will the non-return valves limit flow in any way? Is there a specific
type? Going to pop down plumbase and pick a couple up in a mo....
Roger Mills
Oct 1, 2012, 11:39:37 AM10/1/12
to
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
> 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....
>
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.
--
Cheers,
Roger
____________
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Toby
Oct 1, 2012, 12:22:48 PM10/1/12
to
sure it won't be a problem.
Message has been deleted
Message has been deleted
fred
Oct 1, 2012, 2:47:25 PM10/1/12
to
In article <op.wlif25ksxafqef@desktop>, MarkG <m...@nospam.com> writes
>
>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-3-4-INCH-Pressure-Reducing-Valve-PRV-for-
>15mm-or-22mm-1-5bar-6bar-/261101591356?pt=UK_Home_Garden_Hearing_Coolin
>g_Air&hash=item3ccade1b3c
>
>or a check valve on the hot side to stop the cold going back down.
>
>http://www.ebay.co.uk/itm/BRASS-SINGLE-CHECK-VALVE-15MM-NON-RETURN-
>COMPRESSION-/250688583906?pt=UK_DIY_Materials_Plumbing_MJ&hash=item
>3a5e3438e2
>
>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...
>
I am a bit surprised by your problems. One of the main benefits of combi
boilers is that you get balanced pressure of both hot and cold water
(the hot water comes from the mains too, it just passes thro a heat
exchanger).
A quick look at the installation manual for the boiler shows that it is
suitable for use on mains supply of up to 10bar without the use of a
pressure reducing valve so I wouldn't expect one to be fitted to yours
(it would be on the cold feed to the boiler).
That said, the symptoms you describe do suggest back pressure on the hot
side, reducing or stopping flow and causing the boiler to shut off.
Have a look to see if you can see a pressure reducing valve before the
boiler as that could be an explanation. The manual I looked at did not
show an internal pressure reducing valve.
You also say the mixing valve has a maximum pressure of 5bar so there
may be an issue there too but the bad news is that if you have over 5bar
on both hot and cold then you may need to pressure reduce both.
I don't think a check valve on the hot side will be of benefit as if the
fault is a cold to hot pressure differential then the valve will be held
closed by the pressure diff, no water will flow end the boiler wont
fire.
As an experiment, try opening a hot tap in the bathroom a bit then turn
on the shower valve. If the flow from the hot tap increases then you
have back flow cold to hot.
HTH
--
fred
it's a ba-na-na . . . .
>
>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-3-4-INCH-Pressure-Reducing-Valve-PRV-for-
>15mm-or-22mm-1-5bar-6bar-/261101591356?pt=UK_Home_Garden_Hearing_Coolin
>g_Air&hash=item3ccade1b3c
>
>or a check valve on the hot side to stop the cold going back down.
>
>http://www.ebay.co.uk/itm/BRASS-SINGLE-CHECK-VALVE-15MM-NON-RETURN-
>COMPRESSION-/250688583906?pt=UK_DIY_Materials_Plumbing_MJ&hash=item
>3a5e3438e2
>
>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...
>
I am a bit surprised by your problems. One of the main benefits of combi
boilers is that you get balanced pressure of both hot and cold water
(the hot water comes from the mains too, it just passes thro a heat
exchanger).
A quick look at the installation manual for the boiler shows that it is
suitable for use on mains supply of up to 10bar without the use of a
pressure reducing valve so I wouldn't expect one to be fitted to yours
(it would be on the cold feed to the boiler).
That said, the symptoms you describe do suggest back pressure on the hot
side, reducing or stopping flow and causing the boiler to shut off.
Have a look to see if you can see a pressure reducing valve before the
boiler as that could be an explanation. The manual I looked at did not
show an internal pressure reducing valve.
You also say the mixing valve has a maximum pressure of 5bar so there
may be an issue there too but the bad news is that if you have over 5bar
on both hot and cold then you may need to pressure reduce both.
I don't think a check valve on the hot side will be of benefit as if the
fault is a cold to hot pressure differential then the valve will be held
closed by the pressure diff, no water will flow end the boiler wont
fire.
As an experiment, try opening a hot tap in the bathroom a bit then turn
on the shower valve. If the flow from the hot tap increases then you
have back flow cold to hot.
HTH
--
fred
it's a ba-na-na . . . .
Message has been deleted
MarkG
Oct 1, 2012, 2:57:58 PM10/1/12
to
On Mon, 01 Oct 2012 19:47:25 +0100, fred <n...@for.mail> wrote:
> In article <op.wlif25ksxafqef@desktop>, MarkG <m...@nospam.com> writes
>
> In article <op.wlif25ksxafqef@desktop>, MarkG <m...@nospam.com> writes
>
> You also say the mixing valve has a maximum pressure of 5bar so there
> may be an issue there too but the bad news is that if you have over 5bar
> on both hot and cold then you may need to pressure reduce both.
>
Well it states a maximum "static" pressure of 10bar and a maximumk "flow"
> may be an issue there too but the bad news is that if you have over 5bar
> on both hot and cold then you may need to pressure reduce both.
>
pressure of 5 bar.
What's the difference? - please no wise asses saying 5 bar :-)
MarkG
Oct 1, 2012, 3:05:04 PM10/1/12
to
shower valve is on....
--
fred
Oct 1, 2012, 3:10:03 PM10/1/12
to
In article <op.wlikawzlxafqef@desktop>, MarkG <m...@nospam.com> writes
10 bar, when it is operating (on) however the pressure limit is lower,
5bar.
No idea what the reason for this is, it may be a pressure balance issue
or it may be that post valve sealing is not proof to higher levels.
>On Mon, 01 Oct 2012 19:47:25 +0100, fred <n...@for.mail> wrote:
>
>> In article <op.wlif25ksxafqef@desktop>, MarkG <m...@nospam.com> writes
>
>> You also say the mixing valve has a maximum pressure of 5bar so there
>> may be an issue there too but the bad news is that if you have over 5bar
>> on both hot and cold then you may need to pressure reduce both.
>>
>Well it states a maximum "static" pressure of 10bar and a maximumk "flow"
>pressure of 5 bar.
>
>What's the difference? - please no wise asses saying 5 bar :-)
>
This means that when it is off it wont leak or burst at a pressure up to
>
>> In article <op.wlif25ksxafqef@desktop>, MarkG <m...@nospam.com> writes
>
>> You also say the mixing valve has a maximum pressure of 5bar so there
>> may be an issue there too but the bad news is that if you have over 5bar
>> on both hot and cold then you may need to pressure reduce both.
>>
>Well it states a maximum "static" pressure of 10bar and a maximumk "flow"
>pressure of 5 bar.
>
>What's the difference? - please no wise asses saying 5 bar :-)
>
10 bar, when it is operating (on) however the pressure limit is lower,
5bar.
No idea what the reason for this is, it may be a pressure balance issue
or it may be that post valve sealing is not proof to higher levels.
Roger Mills
Oct 2, 2012, 10:22:16 AM10/2/12
to
On 01/10/2012 19:57, MarkG wrote:
>
> Well it states a maximum "static" pressure of 10bar and a maximumk
> "flow" pressure of 5 bar.
>
> What's the difference? - please no wise asses saying 5 bar :-)
Are you asking why static and flow pressure are different, or why this
>
> Well it states a maximum "static" pressure of 10bar and a maximumk
> "flow" pressure of 5 bar.
>
> What's the difference? - please no wise asses saying 5 bar :-)
device has different limits for the two? Someone else has addressed the
second possibility, so I will address the first.
Static pressure is what you get when there is no flow, so the full
pressure generated by the pump - or whatever is driving it - is seen at
the point of application. Flow pressure is what you get when liquid is
flowing, and is lower than static pressure because some of the pressure
is lost along the way, overcoming flow resistance.
The electrical analogy is to consider the difference of measuring first
the Open Circuit voltage at a point in an electrical circuit, and then
the voltage when current is flowing. The second measurement is lower due
to the internal resistance of the power supply and the resistance of the
cables etc.
MarkG
Oct 2, 2012, 2:08:55 PM10/2/12
to
OK, picked up a pressure gauge from PlumbCentre, measured 4Bar on cold
side and 3.3Bar on the hot side.
So it's below the 5Bar limit, which is good, so the question is, would a
0.7bar difference in pressure cause this sort of problem? Seems like a
VERY picky thermostatic mixer, or is this perfectly normal?
side and 3.3Bar on the hot side.
So it's below the 5Bar limit, which is good, so the question is, would a
0.7bar difference in pressure cause this sort of problem? Seems like a
VERY picky thermostatic mixer, or is this perfectly normal?
Toby
Oct 2, 2012, 4:37:40 PM10/2/12
to
pressure to be the same on both the hot and the cold if they are both
"powered" by the incoming mains supply.
In the PDF you linked to, it shows a non return valve, are you able to
see if this is actually present on the unit you have?
I asked earlier if the pipes were connected the correct way around, are
they (do you get hot water from the shower if the mixer is set to hot only?)
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