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Keith Refson - real email address in signature
 
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Default CH system has no vent on primary

I have posted before about the wonderful Servowarm gas CH system I
inherited with the "new" house, but now as I am preparing to upgrade
the controls and pipework to a more modern configuration I have just
noticed a new twist.

There is apparently no vent pipe on the primary!

In brief the system was installed by servowarm about 12 years ago consisting
of an Elite 50 boiler feeding a fully pumped system and an indirect HW
cylinder. The system appears to be a prehistoric version of a Y-plan
except that the diverter valve is a manual one and for the complete
absence of any thermostats (other than the boiler stat). The primary
circuit is fed from a conventionally set-up expansion tank/cistern
arrangement in the loft which is hooked in just before the diverter
valve splits the feed from the boiler.

I believe the usual recommendation is for a 22mm or larger vent pipe
to discharge over the expansion tank, but there is no sign of this at
all. This leaves just the 15mm feed pipe to the cistern which is far
from straight.

There is a vent pipe on the *secondary* circuit discharges over the
larger cold -water cistern, but this is of course not connected to the
primary.

The only possible safety feature I can see on the primary is a device
fitted to a Tee at the highest point in the primary circuit which I
can not identify. This is a vertical brass cylinder about 5cm high
and 4cm diameter with a screw-on brass lid with an offset plastic
knurled nut just under 1cm diameter with a screw head in the middle.
There's a single 15mm pipe entry at the bottom connected to the
primary circuit.

Can anyone help me identify this device? I'm rather hoping it's some
sort of pressure relief valve, but if not it seems that the system is
potentially dangerous in its current state.

Since I'm redoing some of the pipework anyway, it would actually be a
relatively straightforward matter to install a vent if that's
necessary. I'd very much appreciate a comment from one of the
well-informed regulars on this system and whether adding a vent is
essential or not.

Keith Refson

--
Keith Refson 01865 435302 (Home)
23 Napier Road 07773 074233 (Mobile)
Oxford OX4 3HZ K.Refson AT Ntlworld.com
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Keith Refson - real email address in signature
 
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Default CH system has no vent on primary


Just to follow up my own post,

(Keith Refson - real email address in signature) writes:

I have posted before about the wonderful Servowarm gas CH system I
inherited with the "new" house, but now as I am preparing to upgrade
the controls and pipework to a more modern configuration I have just
noticed a new twist.

There is apparently no vent pipe on the primary!

The only possible safety feature I can see on the primary is a device
fitted to a Tee at the highest point in the primary circuit which I
can not identify. This is a vertical brass cylinder about 5cm high
and 4cm diameter with a screw-on brass lid with an offset plastic
knurled nut just under 1cm diameter with a screw head in the middle.
There's a single 15mm pipe entry at the bottom connected to the
primary circuit.

Can anyone help me identify this device? I'm rather hoping it's some
sort of pressure relief valve, but if not it seems that the system is
potentially dangerous in its current state.



I think I have now identified the device, and it's just an air
separator. See

http://www.rwc.co.uk/rwc/pricelist/heating.htm#air

and scroll down to "Automatic air vents".

http://www.rwc.co.uk/rwc/pricelist/i...g/Air_vent.gif

So am I correct in believing that this company installed a system
which is against recommendations and dangerous as used?

Keith Refson
--
Keith Refson 01865 435302 (Home)
23 Napier Road 07773 074233 (Mobile)
Oxford OX4 3HZ K.Refson AT Ntlworld.com
  #3   Report Post  
Christian McArdle
 
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Default CH system has no vent on primary

There is apparently no vent pipe on the primary!

I'd convert to sealed pressurised operation if the boiler, cylinder and
pipework can take it.

Christian.


  #4   Report Post  
Ed Sirett
 
Posts: n/a
Default CH system has no vent on primary

Keith Refson - real email address in signature wrote:

I have posted before about the wonderful Servowarm gas CH system I
inherited with the "new" house, but now as I am preparing to upgrade
the controls and pipework to a more modern configuration I have just
noticed a new twist.

There is apparently no vent pipe on the primary!

In brief the system was installed by servowarm about 12 years ago consisting
of an Elite 50 boiler feeding a fully pumped system and an indirect HW
cylinder. The system appears to be a prehistoric version of a Y-plan
except that the diverter valve is a manual one and for the complete
absence of any thermostats (other than the boiler stat). The primary
circuit is fed from a conventionally set-up expansion tank/cistern
arrangement in the loft which is hooked in just before the diverter
valve splits the feed from the boiler.

I believe the usual recommendation is for a 22mm or larger vent pipe
to discharge over the expansion tank, but there is no sign of this at
all. This leaves just the 15mm feed pipe to the cistern which is far
from straight.

There is a vent pipe on the *secondary* circuit discharges over the
larger cold -water cistern, but this is of course not connected to the
primary.

The only possible safety feature I can see on the primary is a device
fitted to a Tee at the highest point in the primary circuit which I
can not identify. This is a vertical brass cylinder about 5cm high
and 4cm diameter with a screw-on brass lid with an offset plastic
knurled nut just under 1cm diameter with a screw head in the middle.
There's a single 15mm pipe entry at the bottom connected to the
primary circuit.

Can anyone help me identify this device? I'm rather hoping it's some
sort of pressure relief valve, but if not it seems that the system is
potentially dangerous in its current state.

Since I'm redoing some of the pipework anyway, it would actually be a
relatively straightforward matter to install a vent if that's
necessary. I'd very much appreciate a comment from one of the
well-informed regulars on this system and whether adding a vent is
essential or not.


This is standard fair for Servowarm. You may also find that the header
tank is a manual top up device i.e. not with an auto top-up float valve.
You just have to keep aware of when the sytsem is getting low . 8-(

The boiler may be able to take a sealed primary system if the
manufactuers say so and there is at least one manually (= non-automatic)
overheat cutout. They usually interrupt the thermocouple circuit on this
age of boiler.

However there are so many other difficiencies in the control and
efficiency of the system it might be cheaper to decide do a major
overhaul (likely involving a new boiler).

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
  #5   Report Post  
Keith Refson - real email address in signature
 
Posts: n/a
Default CH system has no vent on primary

Ed Sirett writes:

Keith Refson - real email address in signature wrote:

I have posted before about the wonderful Servowarm gas CH system I
inherited with the "new" house, but now as I am preparing to upgrade
the controls and pipework to a more modern configuration I have just
noticed a new twist.

There is apparently no vent pipe on the primary!


This is standard fair for Servowarm. You may also find that the header
tank is a manual top up device i.e. not with an auto top-up float valve.
You just have to keep aware of when the sytsem is getting low . 8-(


But is it actually dangerous?


The boiler may be able to take a sealed primary system if the
manufactuers say so and there is at least one manually (= non-automatic)
overheat cutout. They usually interrupt the thermocouple circuit on this
age of boiler.


There is another cutout which appeas as you describe. (It tripped once
and needed resetting manually before i could relight the pilot.)

However there are so many other difficiencies in the control and
efficiency of the system it might be cheaper to decide do a major
overhaul (likely involving a new boiler).


I'm actually in the middle of a medium-level overhaul including the
replacement of the manual diverter and conversion to a proper
electronically controlled S-plan system, adding some thermostatic
radiator valves and a pressure bypass valve. So if I am going to add a
vent, now would be a good time!

The trouble with this is that I have spotted the other defect in the
system which is that the expansion tank feed is on the wrong side of
the pump, and a likely culprit for the air ingress problems I have been
seeing.

If I were to move the expansion pipe and add the vent to the boiler
output these would be on opposite sides of the pump, and I'd be asking
for pump-over. I could put the vent and the expansion pipe close
together on the boiler output but would not then cure the air ingress.

The pump is integral to the boiler housing and well separated from the
area I am working on by the cylinder, so it would be a larger
operation than I am happy with to move the pump at this stage.

Funnily enough the boiler itself appears to be performing well and I
don't think it needs changing at this stage. I was rather hoping to
upgrade the rest of the system so a drop-in replacement would be
sensible when it becomes necessary.

Keith Refson

--
Keith Refson 01865 435302 (Home)
23 Napier Road 07773 074233 (Mobile)
Oxford OX4 3HZ K.Refson AT Ntlworld.com


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Christian McArdle
 
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Default CH system has no vent on primary

The trouble with this is that I have spotted the other defect in the
system which is that the expansion tank feed is on the wrong side of
the pump, and a likely culprit for the air ingress problems I have been
seeing.


If you are rejigging the system so much, you really should convert to
pressurised operation rather than faff around with vent pipes, tanks, feeds,
pumping over and airlocks. You will need to check the boiler is suitable,
but the presence of the manually reset cutout is a good sign. It will be far
easier to convert to pressurised operation than to debug a poor vented
design. To convert, a competent DIYer should manage it in a hour or two, if
you exclude removing all the old detritus, tanks etc. Don't forget to add an
additive filling point. Far less hassle than faffing with radiator injectors
that squirt inhibitor over the carpet.

Christian.


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Keith Refson - real email address in signature
 
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Default CH system has no vent on primary

"Christian McArdle" writes:

If you are rejigging the system so much, you really should convert to
pressurised operation rather than faff around with vent pipes, tanks, feeds,
pumping over and airlocks. You will need to check the boiler is suitable,
but the presence of the manually reset cutout is a good sign. It will be far
easier to convert to pressurised operation than to debug a poor vented
design. To convert, a competent DIYer should manage it in a hour or two, if



Is it allowed for a DIY job? I thought this was forbidden, or is that
only for a pressurised secondary circuit?

Keith Refson

I'm not familiar with the design of pressurised primary circuits. Is
there some information you could point me at?

Keith Refson
--
Keith Refson 01865 435302 (Home)
23 Napier Road 07773 074233 (Mobile)
Oxford OX4 3HZ K.Refson AT Ntlworld.com
  #8   Report Post  
Christian McArdle
 
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Default CH system has no vent on primary

Is it allowed for a DIY job? I thought this was forbidden, or is that
only for a pressurised secondary circuit?


The primary circuit is fine for DIY. It is having large volume tanks at
pressure that call for special safety measures.

A boiler primary circuit just needs an expansion vessel, 3 bar pressure
relief valve, detachable filling loop and pressure gauge.

I'm not familiar with the design of pressurised primary circuits. Is
there some information you could point me at?


You can buy a kit that contains all the required parts which may even have
instructions. Fundamentally, you just plumb them into the system anywhere
that can't be totally isolated off from the boiler. The pressure relief
valve needs to be near an external wall. The pressure gauge needs to be next
to the filling loop. The filling loop needs a mains water supply. The
expansion vessel can go anywhere. Often these requirements can be fulfilled
in a single location, next to the boiler.

Look in the FAQ for futher info. www.diyfaq.org.uk.

Christian.


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Ed Sirett
 
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Default CH system has no vent on primary

Keith Refson - real email address in signature wrote:

"Christian McArdle" writes:

If you are rejigging the system so much, you really should convert to
pressurised operation rather than faff around with vent pipes, tanks, feeds,
pumping over and airlocks. You will need to check the boiler is suitable,
but the presence of the manually reset cutout is a good sign. It will be far
easier to convert to pressurised operation than to debug a poor vented
design. To convert, a competent DIYer should manage it in a hour or two, if


Is it allowed for a DIY job? I thought this was forbidden, or is that
only for a pressurised secondary circuit?

Keith Refson

I'm not familiar with the design of pressurised primary circuits. Is
there some information you could point me at?

Well you could start with the SealedCH FAQ below and see what else you
need to know.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
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