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  #1   Report Post  
Terry D
 
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Default Gravity hot water temperature control

I have an old Potterton boiler with gravity hot water and pumped heating.
The system still works very well and seems reasonably efficient (£25 monthly
for a 4 bed detached). However, during the colder months, I have far too
much hot water at too high a temperature. Would it be possible to add a
thermostatically controlled valve to the return from the hot water cylinder
(thus maintaining the vent on the flow pipe) in order to control the hot
water temperature. I have a 3-way motorised valve which I could use by
blanking one of the inlets, and then controlling it from a cylinder stat.
Would I also need a narrow bore by-pass.

Terry D.


  #2   Report Post  
IMM
 
Posts: n/a
Default Gravity hot water temperature control


"Terry D" wrote in message
...

I have an old Potterton boiler with gravity hot water and pumped heating.
The system still works very well and seems reasonably efficient (£25

monthly
for a 4 bed detached). However, during the colder months, I have far too
much hot water at too high a temperature. Would it be possible to add a
thermostatically controlled valve to the return from the hot water

cylinder
(thus maintaining the vent on the flow pipe) in order to control the hot
water temperature. I have a 3-way motorised valve which I could use by
blanking one of the inlets, and then controlling it from a cylinder stat.
Would I also need a narrow bore by-pass.


You can fit a normal DHW blending valve to the cylinder draw-off pipe, not
blocking the open vent. hot in one port from the cylinder, cold in the
other. the outlet is blended to whatever you set it to. They are in
Screwfix or http://www.plumbworld.co.uk

Better still replace the old cast-iron clunker with a modern condensing
boiler with a fully pumped system. Your £25 per month will be down to aprox
£15 per months, saving £120 per year.




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  #3   Report Post  
BillP
 
Posts: n/a
Default Gravity hot water temperature control


"Terry D" wrote in message
...
I have an old Potterton boiler with gravity hot water and pumped heating.
The system still works very well and seems reasonably efficient (£25

monthly
for a 4 bed detached). However, during the colder months, I have far too
much hot water at too high a temperature. Would it be possible to add a
thermostatically controlled valve to the return from the hot water

cylinder
(thus maintaining the vent on the flow pipe) in order to control the hot
water temperature. I have a 3-way motorised valve which I could use by
blanking one of the inlets, and then controlling it from a cylinder stat.
Would I also need a narrow bore by-pass.

Terry D.


Just done exactly this.

Fitted a 2 port spring return zone valve in the return line from the hot
water cylinder, thus leaving the vent unrestricted. Fitted a cylinder
thermostat. Modified the wiring as C plan.


  #4   Report Post  
David Hearn
 
Posts: n/a
Default Gravity hot water temperature control


"IMM" wrote in message
...

"Terry D" wrote in message
...

I have an old Potterton boiler with gravity hot water and pumped

heating.
The system still works very well and seems reasonably efficient (£25

monthly
for a 4 bed detached). However, during the colder months, I have far

too
much hot water at too high a temperature. Would it be possible to add a
thermostatically controlled valve to the return from the hot water

cylinder
(thus maintaining the vent on the flow pipe) in order to control the hot
water temperature. I have a 3-way motorised valve which I could use by
blanking one of the inlets, and then controlling it from a cylinder

stat.
Would I also need a narrow bore by-pass.


You can fit a normal DHW blending valve to the cylinder draw-off pipe, not
blocking the open vent. hot in one port from the cylinder, cold in the
other. the outlet is blended to whatever you set it to. They are in
Screwfix or http://www.plumbworld.co.uk

Better still replace the old cast-iron clunker with a modern condensing
boiler with a fully pumped system. Your £25 per month will be down to

aprox
£15 per months, saving £120 per year.


At a cost of at least £1k (unless you DIY it, but that's back to the thread
we had before...

£120 a year saving, you'd need nearly 10 years to recoup that.

D


  #5   Report Post  
Terry D
 
Posts: n/a
Default Gravity hot water temperature control

IMM wrote:
"Terry D" wrote in message
...

I have an old Potterton boiler with gravity hot water and pumped
heating. The system still works very well and seems reasonably
efficient (£25 monthly for a 4 bed detached). However, during the
colder months, I have far too much hot water at too high a
temperature. Would it be possible to add a thermostatically
controlled valve to the return from the hot water cylinder (thus
maintaining the vent on the flow pipe) in order to control the hot
water temperature. I have a 3-way motorised valve which I could use
by blanking one of the inlets, and then controlling it from a
cylinder stat. Would I also need a narrow bore by-pass.


You can fit a normal DHW blending valve to the cylinder draw-off
pipe, not blocking the open vent. hot in one port from the cylinder,
cold in the other. the outlet is blended to whatever you set it to.
They are in Screwfix or http://www.plumbworld.co.uk

Better still replace the old cast-iron clunker with a modern
condensing boiler with a fully pumped system. Your £25 per month
will be down to aprox £15 per months, saving £120 per year.

Does a condensing boiler necessarily have to be wall mounted with a balanced
flue? My old Potterton is nicely hidden away in a cupboard with no access
to an outside wall and I want to keep it that way. If I hadn't wasted £12 a
month for 20 years on a useless British Gas service contract, I could now
replace my heating system twice over. Sorry, but I'm still really not
convinced about the apparent advantages of condensing boilers, or the
ability of installers & service engineers. BG quoted me over £2000 when my
system was knocking I subsequently sorted it myself for £25. At an alleged
saving of £120 a year, it would take 16 years to recoup my investment. As
I'm 60 now, I don't think I'll bother unless I have to. I'm sitting here
now at a nice comfortable 22 deg.C with a can of lager at 15 deg. :-) Cast
iron rules-OK.

I would be very surprised if any owners of four bed detached houses are
getting away with only £15 monthly for gas heating. Let's have a survey:
1. Type of house (detached, semi etc). 2. No. of beds. 3. Size of house
(small. med or large, or sq metres). 3. Do you also cook by gas? 4. How
much do you pay monthly. 5) Who is your gas supplier?

Terry D.




  #6   Report Post  
IMM
 
Posts: n/a
Default Gravity hot water temperature control


"David Hearn" wrote in message
...

"IMM" wrote in message
...

"Terry D" wrote in message
...

I have an old Potterton boiler with gravity hot water and pumped

heating.
The system still works very well and seems reasonably efficient (£25

monthly
for a 4 bed detached). However, during the colder months, I have far

too
much hot water at too high a temperature. Would it be possible to add

a
thermostatically controlled valve to the return from the hot water

cylinder
(thus maintaining the vent on the flow pipe) in order to control the

hot
water temperature. I have a 3-way motorised valve which I could use

by
blanking one of the inlets, and then controlling it from a cylinder

stat.
Would I also need a narrow bore by-pass.


You can fit a normal DHW blending valve to the cylinder draw-off pipe,

not
blocking the open vent. hot in one port from the cylinder, cold in the
other. the outlet is blended to whatever you set it to. They are in
Screwfix or http://www.plumbworld.co.uk

Better still replace the old cast-iron clunker with a modern condensing
boiler with a fully pumped system. Your £25 per month will be down to

aprox
£15 per months, saving £120 per year.


At a cost of at least £1k (unless you DIY it,


This is DIY. A Ravenheat condensing boiler is £399.



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  #7   Report Post  
IMM
 
Posts: n/a
Default Gravity hot water temperature control


"Terry D" wrote in message
...
IMM wrote:
"Terry D" wrote in message
...

I have an old Potterton boiler with gravity hot water and pumped
heating. The system still works very well and seems reasonably
efficient (£25 monthly for a 4 bed detached). However, during the
colder months, I have far too much hot water at too high a
temperature. Would it be possible to add a thermostatically
controlled valve to the return from the hot water cylinder (thus
maintaining the vent on the flow pipe) in order to control the hot
water temperature. I have a 3-way motorised valve which I could use
by blanking one of the inlets, and then controlling it from a
cylinder stat. Would I also need a narrow bore by-pass.


You can fit a normal DHW blending valve to the cylinder draw-off
pipe, not blocking the open vent. hot in one port from the cylinder,
cold in the other. the outlet is blended to whatever you set it to.
They are in Screwfix or http://www.plumbworld.co.uk

Better still replace the old cast-iron clunker with a modern
condensing boiler with a fully pumped system. Your £25 per month
will be down to aprox £15 per months, saving £120 per year.

Does a condensing boiler necessarily
have to be wall mounted with a balanced
flue?


All domestic versions I have see, yes.

My old Potterton is nicely hidden away
in a cupboard with no access
to an outside wall and I want to keep
it that way.


Kestons can be fitted anywhere with the flue only being cheap plastic drain
pipe.

If I hadn't wasted £12 a
month for 20 years on a useless British Gas
service contract, I could now
replace my heating system twice over.


BG are not good at times.

Sorry, but I'm still really not
convinced about the apparent advantages
of condensing boilers,



Boilers are amongst the worst offenders when it comes to energy wasters in
your home. Boilers alone account for up to a third of all domestic CO2
emissions. If you donít think your boiler should get away with it any
longer, then read on. As the current lifespan of a boiler is 10-15 years,
making the wrong decision about what boiler to have really could mean a life
sentence of wasting money and time and damaging the environment.

A heating system that uses a high efficiency condensing boiler and with the
correct heating controls can save as much as 40% on your fuel bills. It
really is time to shop your old boiler.



see: http://www.saveenergy.co.uk/boilers/

At an alleged saving of £120 a year, it would
take 16 years to recoup my investment.


Your boiler will not last that long.

As I'm 60 now, I don't think I'll bother unless
I have to. I'm sitting here now at a nice comfortable
22 deg.C with a can of lager at 15 deg. :-) Cast
iron rules-OK.


Cast iron is very inefficient. Unless your house is heavily insulated, or
you turn rads off in many rooms, or you have a small house I can't see you
spending £300 on gas per year.

I would be very surprised if any owners
of four bed detached houses are
getting away with only £15 monthly
for gas heating.


That's what I pay, maybe less. I have a condensing boiler.



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  #8   Report Post  
Owain
 
Posts: n/a
Default Gas Use Survey [was: Gravity hot water temperature control]

"Terry D" wrote
| I would be very surprised if any owners of four bed detached
| houses are getting away with only £15 monthly for gas heating.
| Let's have a survey:
| 1. Type of house (detached, semi etc).

Flat

| 2. No. of beds.

1.

| 3. Size of house

27 sq metres

|3. Do you also cook by gas?

No.

| 4. How much do you pay monthly.

Last four bills, recent first, all before adding VAT

July - Oct
740 kWh @ 2.659 p/kWh
= £19.68 - 3.56 prompt payment discount on previous bill

April - July
543 kWh @ 2.659 p/kWh
= £14.44 - 6.36 ppdopb

February - April
1059 kWh @ various rates (price change)
= £25.83 - 7.20 ppdopb

October 2002 - February 2003
2029 kWh @ various rates
= £46.12 - 4.37 ppdopb

| 5. Who is your gas supplier?

Scottish Gas.

Owain

  #9   Report Post  
Andrew
 
Posts: n/a
Default Gravity hot water temperature control

"IMM" wrote in message news:bnpi44

Boilers are amongst the worst offenders when it comes to energy wasters in
your home. Boilers alone account for up to a third of all domestic CO2
emissions. If you don?t think your boiler should get away with it any
longer, then read on. As the current lifespan of a boiler is 10-15 years,
making the wrong decision about what boiler to have really could mean a life
sentence of wasting money and time and damaging the environment.

A heating system that uses a high efficiency condensing boiler and with the
correct heating controls can save as much as 40% on your fuel bills. It
really is time to shop your old boiler.



see: http://www.saveenergy.co.uk/boilers/

At an alleged saving of £120 a year, it would
take 16 years to recoup my investment.


Your boiler will not last that long.


And nor will the new one, from the very data you quote from! What's
the point in recommending someone fit a boiler expected to last 10-15
years when the payback period in their situation is 16 years?

Replace you boiler when it *needs* replacing. Otherwise you're just
contributing to pollution in the manufacture, transport and fitting of
an unneccessary replacement.
  #10   Report Post  
IMM
 
Posts: n/a
Default Gravity hot water temperature control


"Andrew" wrote in message
om...
"IMM" wrote in message news:bnpi44

Boilers are amongst the worst offenders when it comes to energy wasters

in
your home. Boilers alone account for up to a third of all domestic CO2
emissions. If you don?t think your boiler should get away with it any
longer, then read on. As the current lifespan of a boiler is 10-15

years,
making the wrong decision about what boiler to have really could mean a

life
sentence of wasting money and time and damaging the environment.

A heating system that uses a high efficiency condensing boiler and with

the
correct heating controls can save as much as 40% on your fuel bills. It
really is time to shop your old boiler.



see: http://www.saveenergy.co.uk/boilers/

At an alleged saving of £120 a year, it would
take 16 years to recoup my investment.


Your boiler will not last that long.


And nor will the new one, from the very data you quote from! What's
the point in recommending someone fit a boiler expected to last 10-15
years when the payback period in their situation is 16 years?


It is NOT 16 years. Do your sums inc capital costs of replacing the old
clunker. Did you read the web site?

Replace you boiler when it *needs* replacing. Otherwise you're just
contributing to pollution in the manufacture, transport and fitting of
an unneccessary replacement.


That is a moot point.


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  #11   Report Post  
Christian McArdle
 
Posts: n/a
Default Gravity hot water temperature control

Fitted a 2 port spring return zone valve in the return line from the hot
water cylinder, thus leaving the vent unrestricted. Fitted a cylinder
thermostat. Modified the wiring as C plan.


Be very careful. A gravity fed (not just circulated) primary system requires
an unrestricted feed line too, as well as an unrestricted vent. It is now
common practice (to avoid pumping over) to have the vent straight after the
boiler flow and then the feed. If steam is coming from the boiler flow up
the vent, the water can't enter the boiler by that path, but instead needs
an UNRESTRICTED path down the return. You may find that with an old cast
iron setup, that can happen as the flow line is on the return line next to
the boiler. You MUST check, though.

See the following system. If a zone valve is inserted at position 'Z', the
the feed line can't find its way to the boiler return inlet. The boiler flow
outlet is not accessible due to high pressure steam going through that
section up to the vent. You can use this system sometimes, but this would
require the boiler to have all the safety features required for sealed
operation or combined feed/vent systems (i.e. user resetable cutouts etc).


---
/ \
| | |
tank |-------| |
+----+--+ |
| |
feed | | vent
+--+ |
| |
---- | |
/ \ | |
| /-----Z--+-++
| \ | |
| / | +------+
| \--|---|Modern|
|HWC | |Boiler|
+----+ | |
+------+

If the system is old style feed/vent, then there isn't a problem because the
feed is further on. See below (where you can see that feed water can find
its way safely to the boiler):

---
/ \
| | |
|-------| |
+----+--+ |
| |
feed | | vent
+--+ |
| |
---- | |
/ \ | |
| /-----Z----++
| \ | | |
| / | | +------+
| \--|-----+-| Old |
| | |Boiler|
+----+ | |
+------+

This vent/feed arrangement wouldn't work with a modern boiler, as the
pressure difference across the boiler is large. This would cause a similar
pressure difference between feed and vent, causing water to be pumped
through it.

Christian.


  #12   Report Post  
IMM
 
Posts: n/a
Default Gravity hot water temperature control


"Christian McArdle" wrote in message
t...
Fitted a 2 port spring return zone valve in the return line from the hot
water cylinder, thus leaving the vent unrestricted. Fitted a cylinder
thermostat. Modified the wiring as C plan.


Be very careful. A gravity fed (not just circulated) primary system

requires
an unrestricted feed line too, as well as an unrestricted vent. It is now
common practice (to avoid pumping over) to have the vent straight after

the
boiler flow and then the feed. If steam is coming from the boiler flow up
the vent, the water can't enter the boiler by that path, but instead needs
an UNRESTRICTED path down the return. You may find that with an old cast
iron setup, that can happen as the flow line is on the return line next to
the boiler. You MUST check, though.

See the following system. If a zone valve is inserted at position 'Z', the
the feed line can't find its way to the boiler return inlet. The boiler

flow
outlet is not accessible due to high pressure steam going through that
section up to the vent. You can use this system sometimes, but this would
require the boiler to have all the safety features required for sealed
operation or combined feed/vent systems (i.e. user resetable cutouts etc).


---
/ \
| | |
tank |-------| |
+----+--+ |
| |
feed | | vent
+--+ |
| |
---- | |
/ \ | |
| /-----Z--+-++
| \ | |
| / | +------+
| \--|---|Modern|
|HWC | |Boiler|
+----+ | |
+------+


In the above, the pump must be between the zone valve (Z) and the feed &
vent pipes. The feed must be between the vent pipe and the pump, eother on
then p[ressure or suction side.

If the system is old style feed/vent, then there isn't a problem because

the
feed is further on. See below (where you can see that feed water can find
its way safely to the boiler):


But below there is a possibility of pump over. On a modern boiler there is
no need for a direct return path to the boiler for the cold feed. Modern
boilers have double protection stats: run and high limit. The probability
of both failing at the same time is very slim. That is why one pipe system
are permitted - just one 22mm pipe for the F&E tank.

---
/ \
| | |
|-------| |
+----+--+ |
| |
feed | | vent
+--+ |
| |
---- | |
/ \ | |
| /-----Z----++
| \ | | |
| / | | +------+
| \--|-----+-| Old |
| | |Boiler|
+----+ | |
+------+

This vent/feed arrangement wouldn't work with a modern boiler, as the
pressure difference across the boiler is large. This would cause a similar
pressure difference between feed and vent, causing water to be pumped
through it.


It would work, depending where the pump is located.


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  #13   Report Post  
Christian McArdle
 
Posts: n/a
Default Gravity hot water temperature control

(large snip)

I'm getting confused as to what you disagreed with. BTW, no pump was shown,
as the system is unpumped. However, in a pumped system, the pump would in
all cases between the vent (or fill point, if appropriate) and the zone
valve.

In any case, the main issue is to ensure that the filling arrangements are
suitable for the boiler, if the boiler doesn't have the safety features
required for combined fill/vent operation. As the boiler runs a gravity hot
water system, it is likely to lack such features. If the vent/fill
arrangements are like the top system and a zone valve is installed, the
system could be unsafe.

Christian.



  #14   Report Post  
IMM
 
Posts: n/a
Default Gravity hot water temperature control


"Christian McArdle" wrote in message
t...
(large snip)

I'm getting confused as to what you disagreed with. BTW, no pump was

shown,
as the system is unpumped.


You are on about modern and old. Few modern boilers allow gravity these
days. Those that do will not be around for long as legislation will phase
them out.

However, in a pumped system, the pump would in
all cases between the vent (or fill point, if appropriate) and the zone
valve.


With a pump, it should be as I explained.



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  #15   Report Post  
BillR
 
Posts: n/a
Default Gravity hot water temperature control

Christian McArdle wrote:
Fitted a 2 port spring return zone valve in the return line from the
hot water cylinder, thus leaving the vent unrestricted. Fitted a
cylinder thermostat. Modified the wiring as C plan.


[SNIP]
See the following system. If a zone valve is inserted at position
'Z', the the feed line can't find its way to the boiler return inlet.
The boiler flow outlet is not accessible due to high pressure steam

[snip]
OT - but am I missing something as whenever anyone posts ascii diagrams they
look like complete gobbledegook to me?
Shouldn't they be in a fixed font like courier ?




  #16   Report Post  
Christian McArdle
 
Posts: n/a
Default Gravity hot water temperature control

You are on about modern and old. Few modern boilers allow gravity these
days. Those that do will not be around for long as legislation will
phase them out.

With a pump, it should be as I explained.


But the system in question is: "an old Potterton boiler with gravity hot
water and pumped heating".

I'm just saying that the feed/vent arrangements must be examined to be safe
if a zone valve is installed. In particular, the feed to the system must
have clear pipework with no valves all the way to the boiler return (and not
crossing or combining with the vent pipework) unless the boiler is a
"modern" type with overheat cutout.

Christian.



  #17   Report Post  
Christian McArdle
 
Posts: n/a
Default Gravity hot water temperature control

Shouldn't they be in a fixed font like courier ?

Yes. It is up to your newsreader to choose the font. The font selection is
not part of the message, which is just simple unformatted text. Find your
newsreader's settings and change all the fonts to Courier, even the supposed
"variable width" ones.

Christian.


  #18   Report Post  
IMM
 
Posts: n/a
Default Gravity hot water temperature control


"Christian McArdle" wrote in message
t...
Shouldn't they be in a fixed font like courier ?


Yes. It is up to your newsreader to choose the font. The font selection is
not part of the message, which is just simple unformatted text. Find your
newsreader's settings and change all the fonts to Courier, even the

supposed
"variable width" ones.


Or copy all the text into Word and set courier there.


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  #19   Report Post  
BillP
 
Posts: n/a
Default Gravity hot water temperature control


"Christian McArdle" wrote in message
t...

Be very careful. A gravity fed (not just circulated) primary system

requires
an unrestricted feed line too, as well as an unrestricted vent.

Christian.



Good point. The valve is fitted in the airing cupboard in the return line as
it leaves the HW cylinder in the airing cupboard before it tees into the
feed/return line which then runs on to the boiler. Thus the gravity return
is closed off by the valve but the feed and vent is still open.


  #20   Report Post  
BillP
 
Posts: n/a
Default Gravity hot water temperature control


"BillP" wrote in message news:jLdob.399

Thus the gravity return
is closed off by the valve but the feed and vent is still open.


This should have said feed and vent lines are still open.




  #21   Report Post  
David Hearn
 
Posts: n/a
Default Gravity hot water temperature control


"IMM" wrote in message
...

"Christian McArdle" wrote in message
t...
Shouldn't they be in a fixed font like courier ?


Yes. It is up to your newsreader to choose the font. The font selection

is
not part of the message, which is just simple unformatted text. Find

your
newsreader's settings and change all the fonts to Courier, even the

supposed
"variable width" ones.


Or copy all the text into Word and set courier there.


Or even easier, copy into Notepad. Already in a fixed width font, so no
need to change it, and loads heaps quicker than Word.

D


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