Air drawn into sealed system
 

I've been having a problem with air in a sealed system, not huge
amounts but enough to make the system noisy. It only seems to be
noticable when the hot water is on by itself, and i'm not getting much
air in the rads.

- Definately air not hydrogen, and there is plenty of inhibitor in
system.
- Quite a large system, 30KW condensing boiler, 6m head Grundfos Alpha
pump set to max. Pressure vessel is between boiler & pump intake.
- Zone valves are on returns, not feeds.
- Boiler, pump, zone valves etc all downstairs, and there is quite a
long run to HW cylinder (17m of pipework approx).
- System pressure seems to remain constant, and does not drop over
time.

I've pressurised system to 3bar and checked for leaking compression
joints, rad valves etc, everything seems fine.

How long roughly does it normally take for air in the system to clear
after a refill on a sealed system? (note there is no air separator)

I'm pretty sure air is being drawn in, any suggestions to what the most
likely causes could be?

Air drawn into sealed system
 

Yes there is an auto air vent in the airing cupboard.

Maybe the pressure isn't rising as i'm being to efficient at removing
the air as it accumulates? (via a manual air vent above the boiler).

Having said that i haven't bled the rads for a few weeks so don't know
what is in them at the moment.

Air drawn into sealed system
 

On Tue, 04 Apr 2006 03:26:55 -0700, Mary Hinge wrote:

Yes there is an auto air vent in the airing cupboard.

Maybe the pressure isn't rising as i'm being to efficient at removing
the air as it accumulates? (via a manual air vent above the boiler).

Having said that i haven't bled the rads for a few weeks so don't know
what is in them at the moment.

Is the auto-vent functioning?

--
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

Air drawn into sealed system
 

Most definately working.

Air does tend to also get trapped on pipework around the boiler, since
the feed & return drop down 2m immediately before/after the boiler if
you get my drift, i just bleed these using the manual air vents?

Is it really necessary to have auto air vents wherever air tends to
accumulate to ensure all the air comes out of a sealed system? I sort
of assumed that after a short period it would just end up in the rads
where it can be bled out, leaving an air-free system.

My gut feeling is air is being pulled in around the area of the pump
inlet, is this possible and how common is it?

Thanks,

MH

Air drawn into sealed system
 

On Tue, 04 Apr 2006 11:48:56 -0700, Mary Hinge wrote:

Most definately working.

Air does tend to also get trapped on pipework around the boiler, since
the feed & return drop down 2m immediately before/after the boiler if
you get my drift, i just bleed these using the manual air vents?

Is it really necessary to have auto air vents wherever air tends to
accumulate to ensure all the air comes out of a sealed system? I sort
of assumed that after a short period it would just end up in the rads
where it can be bled out, leaving an air-free system.

My gut feeling is air is being pulled in around the area of the pump
inlet, is this possible and how common is it?

The whole system is under pressure. It is possible apparently for a system
to draw in air even though it is under pressure through small leaks.

The auto air vent is a convenience really rather than an absolute
necessity, it can even be closed once all the air is out.

If I were faced with the system professionally then assuming I haven't
missed anything in your posts then I would go for sealing it up with
Fernox LS-I or equivalent.


--
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

Air drawn into sealed system
 

Thanks for the replies :o)

I did bleed a reasonable amount of air from one of the rads yesterday
(it seems to acculumate in just one rad due to the system layout), and
noticed the pressure may have dropped very slightly, so it could be a
small leak somewhere on the pipework that is not visible.

I just surprised that air can still sneak in on a pressurised system,
and that it can make quite a noticeable amount of noise. I'm guessing
this would be a very small, slow leak due to the lack of immediately
noticable pressure drop. The problem did go away about 6 months ago
(after the system was pressurised), but seems to have come back after a
couple of rads were added to the system (all the new pipework looks
watertight).

I'll give the leak sealer a bash and see if that resolves, I assume
this stuff is quite effective and has solved similar issues in the
past?

Many Thanks,

MH

Air drawn into sealed system
 

Two litres of Betz-Dearborn's finest Sentinel leak sealing fluid and
the problem persists :o(

Any other suggestions? This is really starting to get me down...

Cheers,

MH

Air drawn into sealed system
 

On Wed, 12 Apr 2006 03:24:35 -0700, Mary Hinge wrote:

Two litres of Betz-Dearborn's finest Sentinel leak sealing fluid and
the problem persists :o(

Any other suggestions? This is really starting to get me down...

How long has it been in?
Expect to get some air out for the next few weeks - even a system which is
completely air/water tight will take some time to get all the air out.
Have you closed the auto vent yet?

--
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

Air drawn into sealed system
 

Ok thanks - i'll give it a fews weeks and see what happens - yes the
AAV is still open.

Cheers,

MH

Air drawn into sealed system
 

Update: I stumbled across this thread http://tinyurl.com/j86v2 (warning
this is a long read!)

Basically this guy's problem was very similar to mine (I also have a 6m
head pump set to max), in fact i had tried many of the steps he had
(conversion to combined feed & vent etc) also without success, before
going sealed which resolved the air issue, until we had some work done
in the house five months or so later.

After reading this thread I did recall that after the plumber converted
to a sealed system i did notice the cold pressure was quite high, near
1.5 bar, whereas I had been pressurising to around 1.25 bar cold. So a
couple of nights ago I increased the cold pressure to 1.5 bar and
hey-presto, problem solved immediately, no more air.

Whilst i'm relieved that the problem has gone away, I am perplexed as
to how you could have a leak that doesn't let water out, but plenty of
air in unless you pressurise to 1.5 bar? Bear in mind this issue wasn't
a small amount of air, but what seemed like loads, ie the system made
noises you associate with venting a refilled system every time I had
the hot water circuit on by itself.

Any ideas? I don't really feel like I've solved the problem, just found
a work-around.