I had the expansion vessel on my CH boiler repressurised recently.

Now the system pressure is starting to rise imperceptibly again (0.3bar
cold pressure increase over 2 weeks).

Can someone please explain why, if the expansion vessel is losing air
and therefore the CH water has more space, why the CH pressure should
go up and not down? (The pressure guage I assume is on the 'wet' side
of the vessel.)

Thanks.

...Also, if I need to repressurise it myself, what's the simplest way to
do this without completely draining the system?

Bart

In an earlier contribution to this discussion,
Bart wrote:

I had the expansion vessel on my CH boiler repressurised recently.

Now the system pressure is starting to rise imperceptibly again
(0.3bar cold pressure increase over 2 weeks).

Can someone please explain why, if the expansion vessel is losing air
and therefore the CH water has more space, why the CH pressure should
go up and not down? (The pressure guage I assume is on the 'wet' side
of the vessel.)


Odd! I suppose that a possible explanation is that the weather is getting
warmer - so that the system water doesn't cool as much when the heating is
off - but I'm not sure that that would explain it.

Thanks.

..Also, if I need to repressurise it myself, what's the simplest way
to do this without completely draining the system?


You need to set the air pressure with the wet side de-pressurised. You don't
need to drain the system - just let some water out at the fill point - or
from a radiator bleed screw - until the gauge reads zero. And yes - the
pressure gauge *is* on the wet side.

Use a car foot pump (operated by hand) to pressurise the air side to about
0.7 bar (10 psi). Then use the filling loop to re-pressurise the wet system
to your usual cold pressure - probably about 1 bar.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sat, 03 Jun 2006 11:06:07 -0700, Bart wrote:

I had the expansion vessel on my CH boiler repressurised recently.

Now the system pressure is starting to rise imperceptibly again (0.3bar
cold pressure increase over 2 weeks).

Can someone please explain why, if the expansion vessel is losing air
and therefore the CH water has more space, why the CH pressure should
go up and not down? (The pressure guage I assume is on the 'wet' side
of the vessel.)

Thanks.

..Also, if I need to repressurise it myself, what's the simplest way to
do this without completely draining the system?

See FAQ.

Could be filling loop letting by or corrosion.


--
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
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

In an earlier contribution to this discussion,
Ed Sirett wrote:

On Sat, 03 Jun 2006 11:06:07 -0700, Bart wrote:


Can someone please explain why, if the expansion vessel is losing air
and therefore the CH water has more space, why the CH pressure should
go up and not down?


Could be filling loop letting by or corrosion.

That's a very valid point. Is the filling loop permanently connected? [It
shouldn't be!]. If it *is* and if there's a slight leak in the valves,
additional water will flow in from the mains - slowly increasing the
pressure.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

The message
from "Roger Mills" contains these words:

That's a very valid point. Is the filling loop permanently connected? [It
shouldn't be!].

They almost always are though.

--
Skipweasel
Pay no attention to that man behind the curtain.

Roger Mills wrote:
In an earlier contribution to this discussion,
Ed Sirett wrote:

On Sat, 03 Jun 2006 11:06:07 -0700, Bart wrote:


Can someone please explain why, if the expansion vessel is losing air
and therefore the CH water has more space, why the CH pressure should
go up and not down?


Could be filling loop letting by or corrosion.

That's a very valid point. Is the filling loop permanently connected? [It
shouldn't be!]. If it *is* and if there's a slight leak in the valves,
additional water will flow in from the mains - slowly increasing the
pressure.

The loop is disconnected, and there is no leak. There *was* a leak a
couple months back, but that wasn't the cause, and I fixed it anyway.
And the DHW heat exchanger was just replaced.

My fix had been to drain off water every so often, but with no new
water getting in, it's a mystery how the water seems to replenish
itself.

If the expansion vessel had no air at all, I'd imagine the system
pressure would go up (a lot) when hot then down again. But the
behaviour appears to be this regular rise over a period of weeks. Very
strange.

Bart

On Sun, 4 Jun 2006 22:01:11 +0100, Bart wrote
(in article .com):


Roger Mills wrote:
In an earlier contribution to this discussion,
Ed Sirett wrote:

On Sat, 03 Jun 2006 11:06:07 -0700, Bart wrote:


Can someone please explain why, if the expansion vessel is losing air
and therefore the CH water has more space, why the CH pressure should
go up and not down?


Could be filling loop letting by or corrosion.

That's a very valid point. Is the filling loop permanently connected? [It
shouldn't be!]. If it *is* and if there's a slight leak in the valves,
additional water will flow in from the mains - slowly increasing the
pressure.

The loop is disconnected, and there is no leak. There *was* a leak a
couple months back, but that wasn't the cause, and I fixed it anyway.
And the DHW heat exchanger was just replaced.

My fix had been to drain off water every so often, but with no new
water getting in, it's a mystery how the water seems to replenish
itself.

If the expansion vessel had no air at all, I'd imagine the system
pressure would go up (a lot) when hot then down again. But the
behaviour appears to be this regular rise over a period of weeks. Very
strange.

Bart


logic would suggest that if the filling loop is not connected that the water
is entering via the DHW heat exchanger. There aren't any other places where
mains water and the primary circuit come close together.

Could be a dud?

Andy Hall wrote:
On Sun, 4 Jun 2006 22:01:11 +0100, Bart wrote
(in article .com):

My fix had been to drain off water every so often, but with no new
water getting in, it's a mystery how the water seems to replenish
itself.
....
Bart

logic would suggest that if the filling loop is not connected that the water
is entering via the DHW heat exchanger. There aren't any other places where
mains water and the primary circuit come close together.

Could be a dud?

The problem was there with the old heat exchanger (which was full of
sludge). The probability of there being a leak in both the old and new
heat exchangers seems small.

On Sun, 4 Jun 2006 22:59:32 +0100, Bart wrote
(in article .com):

Andy Hall wrote:
On Sun, 4 Jun 2006 22:01:11 +0100, Bart wrote
(in article .com):

My fix had been to drain off water every so often, but with no new
water getting in, it's a mystery how the water seems to replenish
itself.
...
Bart

logic would suggest that if the filling loop is not connected that the water
is entering via the DHW heat exchanger. There aren't any other places where
mains water and the primary circuit come close together.

Could be a dud?

The problem was there with the old heat exchanger (which was full of
sludge). The probability of there being a leak in both the old and new
heat exchangers seems small.


I know, but to quote Sherlock Holmes:

"Once you eliminate the impossible, whatever remains, no matter how
improbable, must be the truth."

I can't think of anywhere else that it can be coming from.

wrote:
On 4 Jun,
Andy Hall wrote:

I know, but to quote Sherlock Holmes:

"Once you eliminate the impossible, whatever remains, no matter how
improbable, must be the truth."

I can't think of anywhere else that it can be coming from.

Either that or corrosion producing hydrogen. Bleeding teh radiators should
determine which.

Well, there are certainly corrosion problems.

What should I get in this case when bleeding the radiators, water or
gas, or some combination? I remember getting slightly foamy liquid
which the engineer who worked on it recently thought was inhibitor.

Anyway the CH has been off the last few weeks; would the gas produced
in the rads still have an effect?

Bart

In an earlier contribution to this discussion,
Bart wrote:


What should I get in this case when bleeding the radiators, water or
gas, or some combination? I remember getting slightly foamy liquid
which the engineer who worked on it recently thought was inhibitor.

If the system is working properly, you should get just clearish water coming
out when you open a radiator bleed valve.

If a gas comes out, you need to investigate further. It is normal to get
some air coming out for a while after the system has been re-filled, but all
the dissolved air should come out in the first few weeks. If corrosion is
occurring because there is insufficient inhibitor in the system, hydrogen
will be produced. If you hold a lighted taper by the valve when you open it,
hydrogen will burn with a blue flame, whereas air will probably blow out the
flame.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sun, 04 Jun 2006 23:23:17 +0100, Andy Hall wrote:

On Sun, 4 Jun 2006 22:59:32 +0100, Bart wrote
(in article .com):

Andy Hall wrote:
On Sun, 4 Jun 2006 22:01:11 +0100, Bart wrote
(in article .com):



I know, but to quote Sherlock Holmes:

"Once you eliminate the impossible, whatever remains, no matter how
improbable, must be the truth."

I can't think of anywhere else that it can be coming from.

It could be pressure generated by acid corrosion? This would be due to
hydrogen being formed so if any radiator needs bleeding the it should be
tested for hydrogen.


--
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
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Mon, 05 Jun 2006 11:37:43 +0100, Roger Mills wrote:

In an earlier contribution to this discussion,
Bart wrote:


What should I get in this case when bleeding the radiators, water or
gas, or some combination? I remember getting slightly foamy liquid
which the engineer who worked on it recently thought was inhibitor.

If the system is working properly, you should get just clearish water coming
out when you open a radiator bleed valve.

If a gas comes out, you need to investigate further. It is normal to get
some air coming out for a while after the system has been re-filled, but all
the dissolved air should come out in the first few weeks. If corrosion is
occurring because there is insufficient inhibitor in the system, hydrogen
will be produced. If you hold a lighted taper by the valve when you open it,
hydrogen will burn with a blue flame, whereas air will probably blow out the
flame.

Take care, there are urban myths around about scorched wall paper/
curtains/hands.


--
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
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Mon, 5 Jun 2006 18:49:03 +0100, Ed Sirett wrote
(in article .uk):

On Sun, 04 Jun 2006 23:23:17 +0100, Andy Hall wrote:

On Sun, 4 Jun 2006 22:59:32 +0100, Bart wrote
(in article .com):

Andy Hall wrote:
On Sun, 4 Jun 2006 22:01:11 +0100, Bart wrote
(in article .com):



I know, but to quote Sherlock Holmes:

"Once you eliminate the impossible, whatever remains, no matter how
improbable, must be the truth."

I can't think of anywhere else that it can be coming from.

It could be pressure generated by acid corrosion? This would be due to
hydrogen being formed so if any radiator needs bleeding the it should be
tested for hydrogen.




I suppose possibly, but it would take a lot of corrosion in such a short time
I would have thought.

On Mon, 05 Jun 2006 20:55:23 +0100, Andy Hall wrote:

On Mon, 5 Jun 2006 18:49:03 +0100, Ed Sirett wrote
(in article .uk):

On Sun, 04 Jun 2006 23:23:17 +0100, Andy Hall wrote:

On Sun, 4 Jun 2006 22:59:32 +0100, Bart wrote
(in article .com):

Andy Hall wrote:
On Sun, 4 Jun 2006 22:01:11 +0100, Bart wrote
(in article .com):



I know, but to quote Sherlock Holmes:

"Once you eliminate the impossible, whatever remains, no matter how
improbable, must be the truth."

I can't think of anywhere else that it can be coming from.

It could be pressure generated by acid corrosion? This would be due to
hydrogen being formed so if any radiator needs bleeding the it should be
tested for hydrogen.




I suppose possibly, but it would take a lot of corrosion in such a short time
I would have thought.

A litres or two of gas would bring the pressure up measurably.


--
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
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards