Need a surface mounted thermostatic mixer shower. Hot pressure is much lower than cold, ie vented cylinder versus mains. Any recommendations, suggestions etc?


NT

wrote in message
...
Need a surface mounted thermostatic mixer shower. Hot pressure is much
lower than cold, ie vented cylinder versus mains. Any recommendations,
suggestions etc?

Plowman is your man.

On Tuesday, 18 July 2017 00:59:58 UTC+1, bm wrote:
tabbypurr wrote in message
...
Need a surface mounted thermostatic mixer shower. Hot pressure is much
lower than cold, ie vented cylinder versus mains. Any recommendations,
suggestions etc?

Plowman is your man.

I don't know where you got that rumour but it's not true


NT

wrote in message
...
On Tuesday, 18 July 2017 00:59:58 UTC+1, bm wrote:
tabbypurr wrote in message
...
Need a surface mounted thermostatic mixer shower. Hot pressure is much
lower than cold, ie vented cylinder versus mains. Any recommendations,
suggestions etc?

Plowman is your man.

I don't know where you got that rumour but it's not true

Surely not? Dave knows all there is to know about ****-all, everyone knows
that.
You are misguided

On 18/07/2017 00:56, wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

A few options... running gravity hot and mains cold is always tricky -
unless you fit non return valves to the hot you may find you just back
fill your hot water cylinder with cold water from the mixer.

Options that would work include using a venturi shower (it uses the cold
pressure to in effect boost the hot), or adding a single impeller pump
and attempting to mix pumped hot and mains cold, or better, a dual
impeller pump and pump both hot and cold (from a dedicated additional
feed from the cold cistern).


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
o.uk...
On 18/07/2017 00:56, wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

A few options... running gravity hot and mains cold is always tricky -
unless you fit non return valves to the hot you may find you just back
fill your hot water cylinder with cold water from the mixer.

Options that would work include using a venturi shower (it uses the cold
pressure to in effect boost the hot), or adding a single impeller pump and
attempting to mix pumped hot and mains cold, or better, a dual impeller
pump and pump both hot and cold (from a dedicated additional feed from the
cold cistern).

Great post John, pity that stupid phucker the ex sound engineer can't post
something similar.

On Tuesday, 18 July 2017 01:39:36 UTC+1, John Rumm wrote:
On 18/07/2017 00:56, tabbypurr wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

A few options... running gravity hot and mains cold is always tricky -
unless you fit non return valves to the hot you may find you just back
fill your hot water cylinder with cold water from the mixer.

yeah, the old one can do that

Options that would work include using a venturi shower (it uses the cold
pressure to in effect boost the hot), or adding a single impeller pump
and attempting to mix pumped hot and mains cold, or better, a dual
impeller pump and pump both hot and cold (from a dedicated additional
feed from the cold cistern).

pump? no no. Venturi it is. Cheers.


NT

On 18/07/2017 01:39, John Rumm wrote:
On 18/07/2017 00:56, wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

A few options... running gravity hot and mains cold is always tricky -
unless you fit non return valves to the hot you may find you just back
fill your hot water cylinder with cold water from the mixer.

Where does the displaced hot water go? Up into the cold water tank? I do
hope it's cast iron, not plastic.

wrote:
Need a surface mounted thermostatic mixer shower. Hot pressure is much lower than cold, ie vented cylinder versus mains. Any recommendations, suggestions etc?


NT


Use a manual valve. Better reliability and control.

On 7/18/2017 1:39 AM, John Rumm wrote:
On 18/07/2017 00:56, wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

A few options... running gravity hot and mains cold is always tricky -
unless you fit non return valves to the hot you may find you just back
fill your hot water cylinder with cold water from the mixer.

Options that would work include using a venturi shower (it uses the cold
pressure to in effect boost the hot), or adding a single impeller pump
and attempting to mix pumped hot and mains cold, or better, a dual
impeller pump and pump both hot and cold (from a dedicated additional
feed from the cold cistern).


I'd go for the last one. Don't get a cheap shed / SF / TS pump, get a
Stuart Turner or at least a metal regenerative one from someone like
Grundfoss.

On 18/07/2017 08:20, GB wrote:
On 18/07/2017 01:39, John Rumm wrote:
On 18/07/2017 00:56, wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

A few options... running gravity hot and mains cold is always tricky -
unless you fit non return valves to the hot you may find you just back
fill your hot water cylinder with cold water from the mixer.

Where does the displaced hot water go? Up into the cold water tank?

Yup.

I do
hope it's cast iron, not plastic.

You would have to spend a long time standing under a cold shower to
displace a whole cylinder full ;-)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Tuesday, 18 July 2017 09:47:45 UTC+1, Capitol wrote:
tabbypurr wrote:
Need a surface mounted thermostatic mixer shower. Hot pressure is much lower than cold, ie vented cylinder versus mains. Any recommendations, suggestions etc?

Use a manual valve. Better reliability and control.

A manual mixer valve is what I'm after. I'm not clear what other option there would be. Maybe I'm misunderstanding what you mean. It needs a protective thermostat to prevent scalding. And a nonreturn valve. On second thoughts I'm not convinced venturi is needed, there is enough HW delivery there. I definitely don't want a pump.


NT

On 18/07/2017 00:56, wrote:
Need a surface mounted thermostatic mixer shower. Hot pressure is much lower than cold, ie vented cylinder versus mains. Any recommendations, suggestions etc?


NT

Would a pressure reducing valve on the cold supply work with a normal mixer?

Cheers
--
Clive

On 18/07/2017 12:33, wrote:
On Tuesday, 18 July 2017 09:47:45 UTC+1, Capitol wrote:
tabbypurr wrote:
Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

Use a manual valve. Better reliability and control.

A manual mixer valve is what I'm after. I'm not clear what other
option there would be.

A manual mixer is basically just a mixer tap - like the Mirra 88 with no
thermostat or pressure balancing "smarts"

Maybe I'm misunderstanding what you mean. It
needs a protective thermostat to prevent scalding.

Manual mixers may not even have that.

And a nonreturn
valve.

That would be separate from the shower valve usually.

On second thoughts I'm not convinced venturi is needed, there
is enough HW delivery there. I definitely don't want a pump.

The issue is whether the DHW has adequate pressure to overcome the back
pressure from the shower head while also being fed with mains cold, and
not permit the cold to flow back up the DHW feed. The double check valve
will certainly stop the backflow, but you may find that its very
difficult or impossible to balance the temperature you want - a tiny
change in cold tap position will have a disproportionate effect on the
shower temperature.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article ,
wrote:
On Tuesday, 18 July 2017 00:59:58 UTC+1, bm wrote:
tabbypurr wrote in message
...
Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

Plowman is your man.

I don't know where you got that rumour but it's not true


Probably because I've got a low pressure Mira thermostatic shower, which
is excellent. High flow, rather than high pressure. But both hot and cold
come from the header tank - via 22mm tube. No idea if using mains cold
would work - I suspect not very well. If there is a big pressure
differential.

--
*Do paediatricians play miniature golf on Wednesdays?

Dave Plowman London SW
To e-mail, change noise into sound.

On Tuesday, 18 July 2017 14:38:56 UTC+1, John Rumm wrote:
On 18/07/2017 12:33, tabbypurr wrote:
On Tuesday, 18 July 2017 09:47:45 UTC+1, Capitol wrote:
tabbypurr wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

Use a manual valve. Better reliability and control.

A manual mixer valve is what I'm after. I'm not clear what other
option there would be.

A manual mixer is basically just a mixer tap - like the Mirra 88 with no
thermostat or pressure balancing "smarts"

that would be ok but for one thing. If cold pressure drops there would be risk of scald, so really I need a thermostat to minimise any risk.

Maybe I'm misunderstanding what you mean. It
needs a protective thermostat to prevent scalding.

Manual mixers may not even have that.

And a nonreturn
valve.

That would be separate from the shower valve usually.

On second thoughts I'm not convinced venturi is needed, there
is enough HW delivery there. I definitely don't want a pump.

The issue is whether the DHW has adequate pressure to overcome the back
pressure from the shower head while also being fed with mains cold, and
not permit the cold to flow back up the DHW feed. The double check valve
will certainly stop the backflow, but you may find that its very
difficult or impossible to balance the temperature you want - a tiny
change in cold tap position will have a disproportionate effect on the
shower temperature.

The main problem with the current aqualisa is that it goes from too hot to too cold over a very narrow range, making it a sod to set the temp usably. The fact that the mechanism has gotten somewhat sticky makes it overly difficult to set. I can do it ok but others find it a headache. It also backfeeds & goes cold if turned on too far. Really one has to understand the issues to set it effectively. Add to that the fact that every so often it completely changes its setting and it can't just be left alone.

I can't help thinking an easy option might be the old fashioned 2 tap approach. But no thermostat :/

I don't really know where to go with it. I don't want to replumb or add a pump because there is enough hot delivery. I want a shower that won't go from ice to steam in one degree of movement, and that has a thermostat for safety.


NT

wrote:
On Tuesday, 18 July 2017 09:47:45 UTC+1, Capitol wrote:
tabbypurr wrote:
Need a surface mounted thermostatic mixer shower. Hot pressure is much lower than cold, ie vented cylinder versus mains. Any recommendations, suggestions etc?

Use a manual valve. Better reliability and control.

A manual mixer valve is what I'm after. I'm not clear what other option there would be. Maybe I'm misunderstanding what you mean. It needs a protective thermostat to prevent scalding. And a nonreturn valve. On second thoughts I'm not convinced venturi is needed, there is enough HW delivery there. I definitely don't want a pump.


NT


Why do you need to prevent scalding? Is the hot supply above 65C? I
find our thermostatic valve is a pain to use, with lousy temperature
control. Our manual control shower valves work perfectly. You can turn
the heat up to max to warm up the shower area and then reduce it to the
shower temperature you desire.

On Tuesday, 18 July 2017 08:20:43 UTC+1, GB wrote:
Where does the displaced hot water go? Up into the cold water tank?

Yes, wherefrom it will overflow into the loft.

(Whether it's a hot or cold overflow is another matter, but irrelevant as far as plasterboard is concerned)

Owain

On 18/07/2017 18:15, wrote:
On Tuesday, 18 July 2017 08:20:43 UTC+1, GB wrote:
Where does the displaced hot water go? Up into the cold water tank?

Yes, wherefrom it will overflow into the loft.

(Whether it's a hot or cold overflow is another matter, but irrelevant as far as plasterboard is concerned)

Hopefully the cold cistern would have an overflow pipe out of the loft...


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message ,
writes
The main problem with the current aqualisa is that it goes from too hot
to too cold over a very narrow range, making it a sod to set the temp
usably. The fact that the mechanism has gotten somewhat sticky makes it
overly difficult to set. I can do it ok but others find it a headache.
It also backfeeds & goes cold if turned on too far. Really one has to
understand the issues to set it effectively. Add to that the fact that
every so often it completely changes its setting and it can't just be
left alone.

I can't help thinking an easy option might be the old fashioned 2 tap
approach. But no thermostat :/

I don't really know where to go with it. I don't want to replumb or add
a pump because there is enough hot delivery. I want a shower that won't
go from ice to steam in one degree of movement, and that has a
thermostat for safety.

Not been following but I noticed your comment about Aqualisa. We have
one installed 23 years ago:-)

When first used, I called the plumber back because I was convinced he
had swapped the hot and cold pipes! In fact the shower control is very
sensitive to flow rates and will not control the water temperature
reliably if you run at a low setting.

Ours is fed by a Stuart Turner double head pump because the header tank
is so low (included attic house). Turning up the wick solved the
problem.

I have replaced the thermostatic control once, lime scale, otherwise
very reliable.


NT

--
Tim Lamb

On 18/07/2017 16:28, wrote:
On Tuesday, 18 July 2017 14:38:56 UTC+1, John Rumm wrote:
On 18/07/2017 12:33, tabbypurr wrote:
On Tuesday, 18 July 2017 09:47:45 UTC+1, Capitol wrote:
tabbypurr wrote:

Need a surface mounted thermostatic mixer shower. Hot
pressure is much lower than cold, ie vented cylinder versus
mains. Any recommendations, suggestions etc?

Use a manual valve. Better reliability and control.

A manual mixer valve is what I'm after. I'm not clear what other
option there would be.

A manual mixer is basically just a mixer tap - like the Mirra 88
with no thermostat or pressure balancing "smarts"

that would be ok but for one thing. If cold pressure drops there
would be risk of scald, so really I need a thermostat to minimise any
risk.

Maybe I'm misunderstanding what you mean. It needs a protective
thermostat to prevent scalding.

Manual mixers may not even have that.

And a nonreturn valve.

That would be separate from the shower valve usually.

On second thoughts I'm not convinced venturi is needed, there is
enough HW delivery there. I definitely don't want a pump.

The issue is whether the DHW has adequate pressure to overcome the
back pressure from the shower head while also being fed with mains
cold, and not permit the cold to flow back up the DHW feed. The
double check valve will certainly stop the backflow, but you may
find that its very difficult or impossible to balance the
temperature you want - a tiny change in cold tap position will have
a disproportionate effect on the shower temperature.

The main problem with the current aqualisa is that it goes from too
hot to too cold over a very narrow range, making it a sod to set the
temp usably. The fact that the mechanism has gotten somewhat sticky
makes it overly difficult to set. I can do it ok but others find it a
headache. It also backfeeds & goes cold if turned on too far. Really
one has to understand the issues to set it effectively. Add to that
the fact that every so often it completely changes its setting and it
can't just be left alone.

That pretty much describes the behaviour one would expect with
significantly unbalanced pressures on the feeds.

I can't help thinking an easy option might be the old fashioned 2 tap
approach. But no thermostat :/

Unlikely to be noticeably different.

I don't really know where to go with it. I don't want to replumb or
add a pump because there is enough hot delivery.

The delivery rate is not really the issue. Its lack of hot pressure (or
too much cold). Taps do an effective job of setting a required delivery
rate regardless of the actual pressure.

I want a shower that
won't go from ice to steam in one degree of movement, and that has a
thermostat for safety.

So you need to fit a thermostatic mixer, and then either boost the hot
pressure, or limit the cold pressure.

You could try using a PRV on the cold feed before the shower. However
even of you get closer to a balance you then potentially still run into
the normal problems with low pressure showers - i.e. you need carefully
considered pipe runs and attention to detail in the ways water take-off
happens elsewhere in the house to maintain decent steady state conditions.

If however you start with high pressure hot and cold, then they tend to
be less influenced by these factors.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article ,
writes
On Tuesday, 18 July 2017 08:20:43 UTC+1, GB wrote:
Where does the displaced hot water go? Up into the cold water tank?

Yes, wherefrom it will overflow into the loft.

(Whether it's a hot or cold overflow is another matter, but irrelevant
as far as plasterboard is concerned)

Owain

Your header tank will (should) have an overflow out of the house.
--
bert

On 18/07/2017 10:03, newshound wrote:
On 7/18/2017 1:39 AM, John Rumm wrote:
On 18/07/2017 00:56, wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

A few options... running gravity hot and mains cold is always tricky -
unless you fit non return valves to the hot you may find you just back
fill your hot water cylinder with cold water from the mixer.

Options that would work include using a venturi shower (it uses the
cold pressure to in effect boost the hot), or adding a single impeller
pump and attempting to mix pumped hot and mains cold, or better, a
dual impeller pump and pump both hot and cold (from a dedicated
additional feed from the cold cistern).


I'd go for the last one. Don't get a cheap shed / SF / TS pump, get a
Stuart Turner or at least a metal regenerative one from someone like
Grundfoss.

We had a cheap, noisy and only just sufficient flow pump. It failed a
while ago and was replaced with brass Grundfoss Watermill one. Far better.

SteveW

On Tuesday, 18 July 2017 20:26:36 UTC+1, John Rumm wrote:
On 18/07/2017 16:28, tabbypurr wrote:
On Tuesday, 18 July 2017 14:38:56 UTC+1, John Rumm wrote:
On 18/07/2017 12:33, tabbypurr wrote:
On Tuesday, 18 July 2017 09:47:45 UTC+1, Capitol wrote:
tabbypurr wrote:

Need a surface mounted thermostatic mixer shower. Hot
pressure is much lower than cold, ie vented cylinder versus
mains. Any recommendations, suggestions etc?

Use a manual valve. Better reliability and control.

A manual mixer valve is what I'm after. I'm not clear what other
option there would be.

A manual mixer is basically just a mixer tap - like the Mirra 88
with no thermostat or pressure balancing "smarts"

that would be ok but for one thing. If cold pressure drops there
would be risk of scald, so really I need a thermostat to minimise any
risk.

Maybe I'm misunderstanding what you mean. It needs a protective
thermostat to prevent scalding.

Manual mixers may not even have that.

And a nonreturn valve.

That would be separate from the shower valve usually.

On second thoughts I'm not convinced venturi is needed, there is
enough HW delivery there. I definitely don't want a pump.

The issue is whether the DHW has adequate pressure to overcome the
back pressure from the shower head while also being fed with mains
cold, and not permit the cold to flow back up the DHW feed. The
double check valve will certainly stop the backflow, but you may
find that its very difficult or impossible to balance the
temperature you want - a tiny change in cold tap position will have
a disproportionate effect on the shower temperature.

The main problem with the current aqualisa is that it goes from too
hot to too cold over a very narrow range, making it a sod to set the
temp usably. The fact that the mechanism has gotten somewhat sticky
makes it overly difficult to set. I can do it ok but others find it a
headache. It also backfeeds & goes cold if turned on too far. Really
one has to understand the issues to set it effectively. Add to that
the fact that every so often it completely changes its setting and it
can't just be left alone.

That pretty much describes the behaviour one would expect with
significantly unbalanced pressures on the feeds.

I can't help thinking an easy option might be the old fashioned 2 tap
approach. But no thermostat :/

Unlikely to be noticeably different.

I don't really know where to go with it. I don't want to replumb or
add a pump because there is enough hot delivery.

The delivery rate is not really the issue. Its lack of hot pressure (or
too much cold). Taps do an effective job of setting a required delivery
rate regardless of the actual pressure.

I want a shower that
won't go from ice to steam in one degree of movement, and that has a
thermostat for safety.

So you need to fit a thermostatic mixer, and then either boost the hot
pressure, or limit the cold pressure.

You could try using a PRV on the cold feed before the shower. However
even of you get closer to a balance you then potentially still run into
the normal problems with low pressure showers - i.e. you need carefully
considered pipe runs and attention to detail in the ways water take-off
happens elsewhere in the house to maintain decent steady state conditions.

If however you start with high pressure hot and cold, then they tend to
be less influenced by these factors.

It's beginning to sound like what I need is a pump, and keep the existing shower.

I don't suppose an old CH circulator would do the job? I have one. And maybe a valve on the cold to tame it a little, not too much.


NT

On 18/07/2017 18:15, wrote:
On Tuesday, 18 July 2017 08:20:43 UTC+1, GB wrote:
Where does the displaced hot water go? Up into the cold water tank?

Yes, wherefrom it will overflow into the loft.

(Whether it's a hot or cold overflow is another matter, but irrelevant as far as plasterboard is concerned)

Owain


What I had in mind was this frightful case, which was much more extreme
than the OP's:-

http://www.telegraph.co.uk/news/ukne...on-to-bed.html

A young mother died when boiling water from a faulty heater poured
through the ceiling as she lay asleep in bed, an inquest heard yesterday.
Sharon Minister, 30, was with her boyfriend, Mark Nicholas, when the
plastic water tank in the loft above her melted and dumped 50 gallons of
boiling water on to them.
Mr Nicholas, 27, survived but Miss Minister died in a specialist burns
unit a week later, the hearing in Helston, Cornwall, was told.
Miss Minister's children Jessica, nine, and Victoria, six, were not hurt
but they ran from the house in Penzance to a neighbour, crying
hysterically: "Mark is bleeding and Mummy is burned."
Mr Nicholas told the inquest that the couple woke in the dark to find
themselves in terrible pain but with no idea what had caused it.
He said his girlfriend had spent 17 months complaining about dampness in
the loft beams but he claimed Penwith Housing Association, which owned
the property, had done nothing about it.
Mr Nicholas said he heard strange bubbling noises coming from the
immersion heater as he went to sleep an hour and a half before the water
came through.

In message ,
writes
It's beginning to sound like what I need is a pump, and keep the
existing shower.

I don't suppose an old CH circulator would do the job? I have one. And
maybe a valve on the cold to tame it a little, not too much.

The nice thing about the Stuart Turner pump set up is the *auto start*
arrangement.

Somebody in here once explained the mechanism but mine just works! You
turn on the shower flow control and the pump starts!

--
Tim Lamb

On 19/07/2017 00:36, wrote:
On Tuesday, 18 July 2017 20:26:36 UTC+1, John Rumm wrote:
On 18/07/2017 16:28, tabbypurr wrote:

I want a shower that
won't go from ice to steam in one degree of movement, and that has a
thermostat for safety.

So you need to fit a thermostatic mixer, and then either boost the hot
pressure, or limit the cold pressure.

You could try using a PRV on the cold feed before the shower. However
even of you get closer to a balance you then potentially still run into
the normal problems with low pressure showers - i.e. you need carefully
considered pipe runs and attention to detail in the ways water take-off
happens elsewhere in the house to maintain decent steady state conditions.

If however you start with high pressure hot and cold, then they tend to
be less influenced by these factors.

It's beginning to sound like what I need is a pump, and keep the existing shower.

Well its an option. Alternatively the venturi shower is designed for
situations such as yours.

Have you measured the actual cold main pressure? It would help to work
out how much boost or cut you need to get things closer to balanced.

Stuart turner to a do one of their entry level Showermate single sided
pumps for around £130... that will do about 2.5 bar IIRC.

I don't suppose an old CH circulator would do the job? I have one.

Not really ideal for the job... many of the entry level ones will have a
maximum head of only 5m (so about 0.5 bar) where you could do with
something closer to 3 probably. Also they lack a mechanism to detect the
onset of flow and power up automatically, and shut off when flow ceases.
Lastly they are not really designed for fresh water applications -
especially if its a hard water area.

And maybe a valve on the cold to tame it a little, not too much.

You could try that first - it might give you a cheap improvement.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 19/07/2017 08:10, GB wrote:
On 18/07/2017 18:15, wrote:
On Tuesday, 18 July 2017 08:20:43 UTC+1, GB wrote:
Where does the displaced hot water go? Up into the cold water tank?

Yes, wherefrom it will overflow into the loft.

(Whether it's a hot or cold overflow is another matter, but irrelevant
as far as plasterboard is concerned)

Owain


What I had in mind was this frightful case, which was much more extreme
than the OP's:-

http://www.telegraph.co.uk/news/ukne...on-to-bed.html


A young mother died when boiling water from a faulty heater poured
through the ceiling as she lay asleep in bed, an inquest heard yesterday.
Sharon Minister, 30, was with her boyfriend, Mark Nicholas, when the
plastic water tank in the loft above her melted and dumped 50 gallons of
boiling water on to them.

Yup, there have been a few cases like that (hence my comment about my
suspicion that there are more serious accidents with gravity hot water
systems). Many of these seem to be caused by electrically heated
cylinders boiling and overflowing into plastic cold cisterns that are
not well enough supported.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 7/18/2017 4:28 PM, wrote:
On Tuesday, 18 July 2017 14:38:56 UTC+1, John Rumm wrote:
On 18/07/2017 12:33, tabbypurr wrote:
On Tuesday, 18 July 2017 09:47:45 UTC+1, Capitol wrote:
tabbypurr wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

Use a manual valve. Better reliability and control.

A manual mixer valve is what I'm after. I'm not clear what other
option there would be.

A manual mixer is basically just a mixer tap - like the Mirra 88 with no
thermostat or pressure balancing "smarts"

that would be ok but for one thing. If cold pressure drops there would be risk of scald, so really I need a thermostat to minimise any risk.

Maybe I'm misunderstanding what you mean. It
needs a protective thermostat to prevent scalding.

Manual mixers may not even have that.

And a nonreturn
valve.

That would be separate from the shower valve usually.

On second thoughts I'm not convinced venturi is needed, there
is enough HW delivery there. I definitely don't want a pump.

The issue is whether the DHW has adequate pressure to overcome the back
pressure from the shower head while also being fed with mains cold, and
not permit the cold to flow back up the DHW feed. The double check valve
will certainly stop the backflow, but you may find that its very
difficult or impossible to balance the temperature you want - a tiny
change in cold tap position will have a disproportionate effect on the
shower temperature.

The main problem with the current aqualisa is that it goes from too hot to too cold over a very narrow range, making it a sod to set the temp usably. The fact that the mechanism has gotten somewhat sticky makes it overly difficult to set. I can do it ok but others find it a headache. It also backfeeds & goes cold if turned on too far. Really one has to understand the issues to set it effectively. Add to that the fact that every so often it completely changes its setting and it can't just be left alone.

I can't help thinking an easy option might be the old fashioned 2 tap approach. But no thermostat :/

I don't really know where to go with it. I don't want to replumb or add a pump because there is enough hot delivery. I want a shower that won't go from ice to steam in one degree of movement, and that has a thermostat for safety.


NT

If you are confident that you have enough hot delivery, just use a
relatively cheap manual low pressure mixer taking the cold feed from
your header tank. I was working to a tight budget when I put my current
shower in many years ago and the ceramic mixer tap (probably Wickes,
possibly Screwfix) is smooth, progressive, and very controllable. I
don't have vulnerable users so don't see the need for thermostatic
control or protection. I do have a double ended pump to get a decent
pressure and flow rate, originally a cheap one until it leaked.

As an aside, I now mount my pumps in a small plastic header tank with a
drain into the shower tray, having had two of them develop leaks.

On Tue, 18 Jul 2017 00:56:09 +0100, wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is much lower than cold, ie vented cylinder versus mains. Any recommendations, suggestions etc?

Wimp, take a cold shower. Soap dissolves in cold water.

--
If Christians want us to believe in a Redeemer, let them act redeemed. -- Voltaire

On 20/07/2017 00:41, James Wilkinson Sword wrote:
On Tue, 18 Jul 2017 00:56:09 +0100, wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is much
lower than cold, ie vented cylinder versus mains. Any recommendations,
suggestions etc?

If its a vented cylinder then it must have a cold header tank. Run cold
from that and use a shower pump.

Mike

On Tuesday, 18 July 2017 00:56:12 UTC+1, tabby wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is much lower than cold, ie vented cylinder versus mains. Any recommendations, suggestions etc?

Am searching for venturi showers. Not seen anything suitable yet.

But this isn't quite adding up. Specs on the units I've seen say for 0.3m or 5m head. But the HW head is 3 floors up, so nearly 2 bar, and the pipework 22mm. There's plenty of HW flow to the bathroom sink, but the shower behaves as if the HW flow & pressure are poor.

Something tells me this is not the setup venturi showers are designed for, and that there is maybe a problem with the mixer rather than the DHW supply.. Or perhaps what's on the mixer's outlet. It's an early 80s aqualisa, no idea what model number.
This was the original shower head:
https://www.showerspares.com/images/...e_025 204.jpg
The mixer is round surface mounted.

Is there significant difference in flow per pressure in shower heads & hoses? What's on there now is some cheap chinese stuff.


NT

On 20/07/2017 23:16, wrote:
On Tuesday, 18 July 2017 00:56:12 UTC+1, tabby wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

Am searching for venturi showers. Not seen anything suitable yet.

But this isn't quite adding up. Specs on the units I've seen say for
0.3m or 5m head. But the HW head is 3 floors up, so nearly 2 bar,

2 bar would be 60' of head...

If you really have that, then unless the mains is at a significantly
higher pressure you should be able to get reasonably performance out of
a mixer with just a bit of pressure reduction on the cold side.

Have you measured the static mains pressure?

and the pipework 22mm. There's plenty of HW flow to the bathroom
sink, but the shower behaves as if the HW flow & pressure are poor.

Something tells me this is not the setup venturi showers are designed
for, and that there is maybe a problem with the mixer rather than the
DHW supply. Or perhaps what's on the mixer's outlet.

Have you checked it with the shower head removed? Is it a hard water
area? Shower heads can restrict flow dramatically, especially if scaled
a bit. The restriction will make the mixing at unbalanced pressures more
"twitchy"





--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Friday, 21 July 2017 00:59:21 UTC+1, John Rumm wrote:
On 20/07/2017 23:16, tabbypurr wrote:
On Tuesday, 18 July 2017 00:56:12 UTC+1, tabby wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

Am searching for venturi showers. Not seen anything suitable yet.

But this isn't quite adding up. Specs on the units I've seen say for
0.3m or 5m head. But the HW head is 3 floors up, so nearly 2 bar,

2 bar would be 60' of head...

no... 3 floors is about 20-25' so 2/3 bar not 2 bar.

If you really have that, then unless the mains is at a significantly
higher pressure you should be able to get reasonably performance out of
a mixer with just a bit of pressure reduction on the cold side.

Have you measured the static mains pressure?

No I don't have a measuring wotsit. But at any given flow knob setting presumably a service valve could help equalise pressures more nearly.

and the pipework 22mm. There's plenty of HW flow to the bathroom
sink, but the shower behaves as if the HW flow & pressure are poor.

Something tells me this is not the setup venturi showers are designed
for, and that there is maybe a problem with the mixer rather than the
DHW supply. Or perhaps what's on the mixer's outlet.

Have you checked it with the shower head removed? Is it a hard water
area? Shower heads can restrict flow dramatically, especially if scaled
a bit. The restriction will make the mixing at unbalanced pressures more
"twitchy"

I'm going to check it like that, I suspect that may be part of the problem. The shower mixer has endured 35 years or so of scaly water, though the head & hose are recent.


NT

On Friday, 21 July 2017 01:48:52 UTC+1, tabby wrote:

Would the HW feed be better off with a single or double nonreturn valve? I presume the latter would have more impact on flow.


NT

In message , John
Rumm writes
On 20/07/2017 23:16, wrote:
On Tuesday, 18 July 2017 00:56:12 UTC+1, tabby wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

Am searching for venturi showers. Not seen anything suitable yet.

But this isn't quite adding up. Specs on the units I've seen say for
0.3m or 5m head. But the HW head is 3 floors up, so nearly 2 bar,

2 bar would be 60' of head...

If you really have that, then unless the mains is at a significantly
higher pressure you should be able to get reasonably performance out of
a mixer with just a bit of pressure reduction on the cold side.

Have you measured the static mains pressure?

and the pipework 22mm. There's plenty of HW flow to the bathroom
sink, but the shower behaves as if the HW flow & pressure are poor.

Something tells me this is not the setup venturi showers are designed
for, and that there is maybe a problem with the mixer rather than the
DHW supply. Or perhaps what's on the mixer's outlet.

Have you checked it with the shower head removed? Is it a hard water
area? Shower heads can restrict flow dramatically, especially if scaled
a bit. The restriction will make the mixing at unbalanced pressures
more "twitchy"

The thermostatic control in our 22 year old Aqualisa has been changed
twice despite being fed from the water softener.

Shower doctor dot com

--
Tim Lamb

On 21/07/2017 01:48, wrote:
On Friday, 21 July 2017 00:59:21 UTC+1, John Rumm wrote:
On 20/07/2017 23:16, tabbypurr wrote:
On Tuesday, 18 July 2017 00:56:12 UTC+1, tabby wrote:

Need a surface mounted thermostatic mixer shower. Hot pressure
is much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

Am searching for venturi showers. Not seen anything suitable
yet.

But this isn't quite adding up. Specs on the units I've seen say
for 0.3m or 5m head. But the HW head is 3 floors up, so nearly
2 bar,

2 bar would be 60' of head...

no... 3 floors is about 20-25' so 2/3 bar not 2 bar.

With careful piping and a shower designed for low pressure operation,
2/3rds bar would be ok with the same pressure feed and flow on both
feeds. Its going to be very difficult however if you are attempting to
mix with a source at say 3 bar or more.

If you really have that, then unless the mains is at a
significantly higher pressure you should be able to get reasonably
performance out of a mixer with just a bit of pressure reduction on
the cold side.

Have you measured the static mains pressure?

No I don't have a measuring wotsit.

Might be worth getting one, so you have a feel from the magnitude f the
problem you are trying to solve. Probably only 10 to 15 quid from a
plumber's merchant.

But at any given flow knob
setting presumably a service valve could help equalise pressures more
nearly.

A service valve can throttle the maximum flow rate, but it won't reduce
the pressure. So if you attempt to to mix with a low pressure DHW, and
then apply enough flow resistance to the outlet of the mixer, you will
still likely back feed the DHW.

You need a PRV. One like:

https://www.toolstation.com/shop/p11827?table=no

Might be handy since it shows you what output pressure you are getting.

and the pipework 22mm. There's plenty of HW flow to the bathroom
sink, but the shower behaves as if the HW flow & pressure are
poor.

Something tells me this is not the setup venturi showers are
designed for, and that there is maybe a problem with the mixer
rather than the DHW supply. Or perhaps what's on the mixer's
outlet.

Have you checked it with the shower head removed? Is it a hard
water area? Shower heads can restrict flow dramatically, especially
if scaled a bit. The restriction will make the mixing at unbalanced
pressures more "twitchy"

I'm going to check it like that, I suspect that may be part of the
problem. The shower mixer has endured 35 years or so of scaly water,
though the head & hose are recent.

You may find you need to specifically look for a head that is designed
for low pressure operation.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 21/07/2017 02:04, wrote:
On Friday, 21 July 2017 01:48:52 UTC+1, tabby wrote:

Would the HW feed be better off with a single or double nonreturn valve? I presume the latter would have more impact on flow.

Single would be better (double is only usually a requirement when
protecting a public water supply from contamination).

However you may just find that the cold pressure forces it shut and you
get no HW flow at all.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article ,
Muddymike wrote:
Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

If its a vented cylinder then it must have a cold header tank. Run cold
from that and use a shower pump.

You don't need a pump with adequate sized pipework (with careful pipe
runs) and a low pressure shower.

--
*Honk if you love peace and quiet.

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 21 Jul 2017 13:20:54 +0100, Dave Plowman (News) wrote:

In article ,
Muddymike wrote:
Need a surface mounted thermostatic mixer shower. Hot pressure is
much lower than cold, ie vented cylinder versus mains. Any
recommendations, suggestions etc?

If its a vented cylinder then it must have a cold header tank. Run cold
from that and use a shower pump.

You don't need a pump with adequate sized pipework (with careful pipe
runs) and a low pressure shower.

Why not just have a normal electric shower? Mains pressure, heated as you use it.

--
The man who fell into an upholstery machine is fully recovered.