I've just had a completely new system installed. The boiler is a BAXI
'System' 35/60 with pump and expansion vessel built in. We have 6
Radiators plus indirect cyclinder and a 3 way valve.

My question is this. As long as I leave the system running, ie HW
and/or CH demand on 'all day' the pressure sits between 1 and 1.5 bar
all week, or for as long as you keep it all running.

If I let the system go off, ie do not programme CH or HW to come on at
all (say over night), and allow everything to cool right down the
pressure drops right down to almost 0 by the morning.

I have been all over the system and cannot find any leaks and it only
takes a small amount of water through the filling loop to bring the
pressure back up.

My question is this. Why does the pressure only drop when the system is
allowed to cool right down? and could it be related to this... In the
commissioning stage of the install instructions for the boiler it says
to open the screw on the automatic air valve in the boiler. It does not
mention closing it again. I have checked and the screw is definately
loose (open). Is this correct? Or should it be closed once the system
is filled and bled?

On 31 Jan 2005 03:04:36 -0800, "kmillar" wrote:

I've just had a completely new system installed. The boiler is a BAXI
'System' 35/60 with pump and expansion vessel built in. We have 6
Radiators plus indirect cyclinder and a 3 way valve.

Its not critical but your sealed system should be about 1 bar or so
when cold and between 1 and 2 when up to full temp. If there are no
leaks present then the key might be that its a new system. When new,
the system has been filled with oxygenated fresh water,,obviously
there is some settlement and so the pressure drops back a bit,,top it
up when cold to read 1 to 1.3 bar. Observe it over a few weeks and
ensure that the cold pressure remains the same. If not,you probably
have a very small leak somewhere.

By the way,the pressure varies with temp simple because hot water
expands and occupies a greater volume. As yours is a sealed system,it
has nowhere to expand to apart from into. The expansion vessel takes
up most of the expansion but some pressurisation does occur....

joe

Thank you for the reply.
BTW, do you know wether the screw on the "auto air vent" in the boiler
should be open or closed?

In an earlier contribution to this discussion,
kmillar wrote:

I've just had a completely new system installed. The boiler is a BAXI
'System' 35/60 with pump and expansion vessel built in. We have 6
Radiators plus indirect cyclinder and a 3 way valve.

My question is this. As long as I leave the system running, ie HW
and/or CH demand on 'all day' the pressure sits between 1 and 1.5 bar
all week, or for as long as you keep it all running.

If I let the system go off, ie do not programme CH or HW to come on at
all (say over night), and allow everything to cool right down the
pressure drops right down to almost 0 by the morning.

I have been all over the system and cannot find any leaks and it only
takes a small amount of water through the filling loop to bring the
pressure back up.

My question is this. Why does the pressure only drop when the system
is allowed to cool right down? and could it be related to this... In
the commissioning stage of the install instructions for the boiler it
says to open the screw on the automatic air valve in the boiler. It
does not mention closing it again. I have checked and the screw is
definately loose (open). Is this correct? Or should it be closed once
the system is filled and bled?

1 - 1.5 bar is a bit low for a hot system. If you use the filling loop to
charge it up to 1 bar *cold*, does it *still* only get up to 1.5 hot and
then go back to zero when it cools?

If so - and possibly indicated by the fact that it only takes a small amount
of water to re-charge it - it sounds to me as if you could have a problem
with the pressure vessel. If this isn't working properly, it can't absorb
the expansion when the water gets hot - so pressure builds up (for a short
time which you might miss) to over 3 bar - whereupon the pressure relief
valve opens and lets some water out. You can test this by tying a plastic
bag round the end of the discharge pipe (which should go out through a wall
into fresh air) and seeing whether any water collects in the bag. If it
does, come back - and we'll tell you what to do next.

I would close the auto air valve once the system is fully bled. I doubt
whether this is the source of your problem unless there is any evidence of
*water* having come out through it.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

I found the problem.

I had a leak which only leaked when the system was cold. I've reapired
the leak and the problem has gone away.

-K

In article . com,
"kmillar" writes:
I found the problem.

I had a leak which only leaked when the system was cold.

This is quite common, except I suspect it's more a case
of it only showing when system is cold -- when system is
hot, it dries up as fast as it leaks.

I've reapired the leak and the problem has gone away.

--
Andrew Gabriel

This is quite common, except I suspect it's more a case
of it only showing when system is cold -- when system is
hot, it dries up as fast as it leaks.

Not quite, because the water pressure never dropped while the system
was hot - it could run for days (and nights obviously) with no trouble.
Only when I let the system go cold did the leak appear.

As it happens, some parts of the install are using PE-X plastic pipe,
and I think they are moving when heating/cooling and had highlighted a
poor joint when they cooled, and moved again.