Nearly a year ago I changed the old vented system to a sealed one,
whilst also adding new rads and splitting it into zones. It all works
well BUT the pressure falls VERY slowly, probably from 1 bar to 0.7 bar
over about 6 weeks.
I can't find any dampness around the rad valves or visible joints so
have resigned myself to waiting for the leak to get worse before I can
find it. Are there any suggestions on how to find the leak, or for
anything I can add to seal the leak (probably not a good idea)?

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?

Dave

In ,
Dave scribed:
Nearly a year ago I changed the old vented system to a sealed one,
whilst also adding new rads and splitting it into zones. It all works
well BUT the pressure falls VERY slowly, probably from 1 bar to 0.7 bar
over about 6 weeks.
I can't find any dampness around the rad valves or visible joints so
have resigned myself to waiting for the leak to get worse before I can
find it. Are there any suggestions on how to find the leak, or for
anything I can add to seal the leak (probably not a good idea)?

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?

Dave

Have you checked the pressure of the CH Expansion vessel? (Don't forget to
depressurise the CH first) On my Vaillant, it should be between 0.7 - 0.9
bar. It should have a car-tyre type valve located on it around the base of
the unit which you can check using a car tyre pressure gauge or similar.

Are you seeing any drips coming from the pressure relief valve outlet pipe,
to indicate either that the valve seat is not closing tightly either due to
grit or that the system doesn't have an effective 'shock absorber' because
the expansion vessel has failed?

There is a good FAQ on this he
http://www.makewrite.demon.co.uk/SealedCH.html

hth
Nigel

"Dave" wrote in message
...
Nearly a year ago I changed the old vented system to a sealed one, whilst
also adding new rads and splitting it into zones. It all works well BUT
the pressure falls VERY slowly, probably from 1 bar to 0.7 bar over about
6 weeks.
I can't find any dampness around the rad valves or visible joints so have
resigned myself to waiting for the leak to get worse before I can find it.
Are there any suggestions on how to find the leak, or for anything I can
add to seal the leak (probably not a good idea)?

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?

Dave

I take it you've got a pressure relief valve vented safely to the outside?
Is this pipe dripping?

Alternitavely, I take it you've installed an expansion vessel into the
system - has this got the correct charge (Around 0.7 bar cold)?

Angus

Angus

Fentoozler wrote:
"Dave" wrote in message
...

Nearly a year ago I changed the old vented system to a sealed one, whilst
also adding new rads and splitting it into zones. It all works well BUT
the pressure falls VERY slowly, probably from 1 bar to 0.7 bar over about
6 weeks.
I can't find any dampness around the rad valves or visible joints so have
resigned myself to waiting for the leak to get worse before I can find it.
Are there any suggestions on how to find the leak, or for anything I can
add to seal the leak (probably not a good idea)?

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?

Dave


I take it you've got a pressure relief valve vented safely to the outside?
Is this pipe dripping?

Alternitavely, I take it you've installed an expansion vessel into the
system - has this got the correct charge (Around 0.7 bar cold)?

Angus

Angus



No drips.
The expansion vessel is built-in to the boiler (30SXi).

Dave

"Dave" wrote in message
...
Fentoozler wrote:
"Dave" wrote in message
...

Nearly a year ago I changed the old vented system to a sealed one, whilst
also adding new rads and splitting it into zones. It all works well BUT
the pressure falls VERY slowly, probably from 1 bar to 0.7 bar over about
6 weeks.
I can't find any dampness around the rad valves or visible joints so have
resigned myself to waiting for the leak to get worse before I can find
it. Are there any suggestions on how to find the leak, or for anything I
can add to seal the leak (probably not a good idea)?

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?

Dave


I take it you've got a pressure relief valve vented safely to the
outside? Is this pipe dripping?

Alternitavely, I take it you've installed an expansion vessel into the
system - has this got the correct charge (Around 0.7 bar cold)?

Angus

Angus

No drips.
The expansion vessel is built-in to the boiler (30SXi).

Dave

Auto-Air-Vent leaking (behind pump inside boiler)? You've got pressure
leaving the system somewhere - check the tails on all the rads.

Angus

In article ,
Dave writes:
Nearly a year ago I changed the old vented system to a sealed one,
whilst also adding new rads and splitting it into zones. It all works
well BUT the pressure falls VERY slowly, probably from 1 bar to 0.7 bar
over about 6 weeks.
I can't find any dampness around the rad valves or visible joints so
have resigned myself to waiting for the leak to get worse before I can
find it. Are there any suggestions on how to find the leak, or for
anything I can add to seal the leak (probably not a good idea)?

A leak that slow probably evaporates before a drip forms.
You are more likely to find it with the heating off (cold),
and the pressure increased to the hot running pressure.
I suggest you leave this until summer when the heating is
off.

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?

1 bar will ensure pipework up to 30 feet above the pressure
guage is pressurised, which is enough for most houses. In a
3 or more storey house with the pressure guage in the basement,
you will need higher pressure if the pipework extends more than
30 feet in height above the pressure guage. (The pressure at 33
feet above the pressure guage will be 1 bar less than the guage
reads.)

Also, the boiler probably has a pressure loss detector which
will lockout the boiler if the pressure drops below something
like 1/4 - 1/2 bar.

As nrh said, check the FAQ too.

--
Andrew Gabriel

In ,
Dave scribed:


No drips.
The expansion vessel is built-in to the boiler (30SXi).


What do you mean by 'built-in'? If you mean it is an integral component of
the boiler unit hung on the wall, then yes, so is mine, but it can still
fail/leak. Can you not take a pressure reading of that expansion vessel
alone?

As suggested in the FAQ, (and I have had to resort to this while I await the
arrival on my new expansion vessel), try creating a temporary expansion
'vessel' from one of the least used rads on the circuit. You'll have to
drain it of liquid first, and then shut off just one of the valves allowing
one connection to operate as the pressure 'overflow' into the rad. When I
did that, my pressure loss which was previously at around half a bar per
day, almost stopped completely and now drops less than that in a week. ;-)

hth
Nigel

On Thu, 05 Jan 2006 17:33:17 +0000, Dave wrote:

Nearly a year ago I changed the old vented system to a sealed one,
whilst also adding new rads and splitting it into zones. It all works
well BUT the pressure falls VERY slowly, probably from 1 bar to 0.7 bar
over about 6 weeks.
I can't find any dampness around the rad valves or visible joints so
have resigned myself to waiting for the leak to get worse before I can
find it. Are there any suggestions on how to find the leak, or for
anything I can add to seal the leak (probably not a good idea)?

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?

Loads of background info in the Sealed CH FAQ.
I doubt the relief valve is dripping but do check.

It will be almost impossible to find a leak that small.
I suggest that you partially drain down and add some internal leak sealer.
(fernox and sentinel do versions), this should seal the tiny leak up.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Fentoozler wrote:
.... snipped

Auto-Air-Vent leaking (behind pump inside boiler)? You've got pressure
leaving the system somewhere - check the tails on all the rads.

Angus



Thanks for that one, I'd forgotten about the auto vent.
I'll check when I can next leave the system cold.

Dave

nrh wrote:
.... snipped

As suggested in the FAQ, (and I have had to resort to this while I await the
arrival on my new expansion vessel), try creating a temporary expansion
'vessel' from one of the least used rads on the circuit. You'll have to
drain it of liquid first, and then shut off just one of the valves allowing
one connection to operate as the pressure 'overflow' into the rad. When I
did that, my pressure loss which was previously at around half a bar per
day, almost stopped completely and now drops less than that in a week. ;-)

hth
Nigel


Thanks for pointing that out (and for reminding me to look at the FAQ)
but I can't see how adding additional expansion capacity can reduce
leakage, do you mean that your old expansion vessel was faulty?

Dave

In news Ed Sirett scribed:


I don't think you actually have to shut off both valves.

Both? I have only turned off just the one.

When you refill
the water will enter the radiator about half way up. So you can still get
some heating and you won't be sending any air round the circuit.

Duly noted, thanks Ed.

Nigel

Andrew Gabriel wrote:
.... snipped


The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?


1 bar will ensure pipework up to 30 feet above the pressure
guage is pressurised, which is enough for most houses. In a
3 or more storey house with the pressure guage in the basement,
you will need higher pressure if the pipework extends more than
30 feet in height above the pressure guage. (The pressure at 33
feet above the pressure guage will be 1 bar less than the guage
reads.)

.... snipped

Sorry, I don't understand that explanation. The system is sealed,
therefore it's all at the same pressure; how does atmospheric pressure
(32 ft of water) affect anything?

Dave

Ed Sirett wrote:
On Thu, 05 Jan 2006 17:33:17 +0000, Dave wrote:


Nearly a year ago I changed the old vented system to a sealed one,
whilst also adding new rads and splitting it into zones. It all works
well BUT the pressure falls VERY slowly, probably from 1 bar to 0.7 bar
over about 6 weeks.
I can't find any dampness around the rad valves or visible joints so
have resigned myself to waiting for the leak to get worse before I can
find it. Are there any suggestions on how to find the leak, or for
anything I can add to seal the leak (probably not a good idea)?

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?


Loads of background info in the Sealed CH FAQ.
I doubt the relief valve is dripping but do check.

It will be almost impossible to find a leak that small.
I suggest that you partially drain down and add some internal leak sealer.
(fernox and sentinel do versions), this should seal the tiny leak up.


Thanks Ed, it looks like the bottom line is that it's nothing too much
to worry about; I'll add the sealer next time I need to drain down.

Another question:
When I did the initial design I was worried that the internal expansion
vessel wouldn't be enough for the size of the system (16 rads) so I was
expecting to have to add an additional one. I was expecting to see a
large increase in pressure from cold to hot but I've been surprised at
how little it varies - maybe an increase of 0.2 at the most. Did I just
overestimate the volume of water (and a small pressure increase is
normal) or might there be something else going on?

Dave

In ,
Dave scribed:



Thanks for pointing that out (and for reminding me to look at the FAQ)
but I can't see how adding additional expansion capacity can reduce
leakage, do you mean that your old expansion vessel was faulty?

Dave

Yes, and still is as it remains in place until my new one arrives (hopefully
tomorrow).
It puzzled me too as to why it should improve although the 'leak' is still
there, so I assumed one of two things is happening. Either the perforation
in the inner airbag has been 'sealed' shut by the pressure of the
surrounding water which I assume now fills the expansion vessel where the
air would previously have been. Or, that the PRV (pressure relief valve) was
opening under pressure when water heated up and was gently dumping water
(and hence system pressure) out of the escape pipe leading to the outside.
Although I could occasionally see drips hanging off the end, I was going to
check that by attaching a polythene bag to the end of the pipe. But as the
boiler is located on the first floor, it's a bit of a clamber up to it on a
pretty long ladder. And I'm not good with heights! :-( So I just decided to
live with the minimal loss of pressure now that the spare rad is taking the
strain as a make-shift expansion vessel. Case of not looking the gift horse
in the mouth, I guess!

Nigel

In article ,
Dave writes:

Sorry, I don't understand that explanation. The system is sealed,
therefore it's all at the same pressure;

It's not at the same pressure. The weight of water increases
the pressure linearly as you go lower down the system. It
increases by 1 bar every 33 feet (and conversely decreases
by 1 bar every 33 feet above any given point). The pressure
guage only tells you what the pressure is at the height of
the guage itself, but you can work out the pressure at every
other point in the system by knowing its height above or below
the pressure guage.

(The pump can generate a differential pressure on top of this
of a couple of feet or so at different points in the system,
but that's rather insignificant in the scale of things).

how does atmospheric pressure
(32 ft of water) affect anything?

Well, you probably don't want the water at lower pressure than
atmospheric at any point in the system.

--
Andrew Gabriel

In article , Dave
writes
Nearly a year ago I changed the old vented system to a sealed one,
whilst also adding new rads and splitting it into zones. It all works
well BUT the pressure falls VERY slowly, probably from 1 bar to 0.7 bar
over about 6 weeks.
I can't find any dampness around the rad valves or visible joints so
have resigned myself to waiting for the leak to get worse before I can
find it. Are there any suggestions on how to find the leak, or for
anything I can add to seal the leak (probably not a good idea)?

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?

Wot everyone said but also look for stains rather than drips, the leak rate
you describe is very low and will likely evaporate before you see moisture
on a hot system. Fernox and related corrosion inhibitors will leave a brown
stain on evaporation & that is what to look for. I had a similarly slow leak
for a very long time and eventually traced it to a very silly & obvious
position but all I saw was the stain on a pipe, no sign of moisture at all.

HTH
--
fred
Plusnet - I hope you like vanilla