I checked the pressure on the expansion vessel with the boiler "quiet"
and this showed 2.25 bar. According to the technical data in the
manual:
Expansion vessel charge pressu 3 bar
Expansion valve setting: 6 bar
On the expansion vessel itself (this is a large silver container at the
front of the boiler) it shows that the vessel should be set at 1 bar.
I'm therefore a little confused at these different figures, so I tried
a couple of different settings!
When set at 3 bar the pressure gauge on the boiler went up quickly
within about 5 minutes and it started venting water. I then released
some pressure, down to 1.5 bar and this reduced the pressure shown in
the gauge to just below 2 where it hovered for a short time before
jumping up to over 3 bar again and started leaking.
So, setting the expansion vessel pressure to 1.5 or 3 bar doesn't seem
to solve the problem and appears to just affect how quickly the boiler
starts loosing water.
I did determine that no water is leaking out of the expansion vessel
valve so I guess this means that it isn't punctured.
Any comments on my findings?
Paul.
Ed Sirett wrote:
On Thu, 30 Mar 2006 04:28:29 -0800, Milleniumaire wrote:
I have a Saunier Duval Thelia Twin 28E combination boiler which was
installed when the house was built seven years ago. Over the last 3/4
years it has caused us a lot of problems usually due to lack of
pressure but for the last 8 months (since it was last repaired) it has
been okay.
Now it is loosing pressure so quickly that it needs to be topped up
every 3/4 hours. I have placed a bucket underneath and this is
catching water leaking from an overflow pipe under the boiler. There
is also an overflow pipe outside but this is dry. The boiler only
seems to leak when I initially top up the pressure, it then settles
down, but after 3/4 hours has lost so much pressure that it cuts out.
I have found that if I turn down the CH thermostat so that the boiler
is off and ensure no hot water is being used, then I allow water in to
top the pressure up, the pressure still falls slightly over a short
period e.g. 15 minutes even though the boiler isn't being used. During
this period no water is seen to be coming out of the overflow pipe
under the boiler. Initially, this suggested to me that I had a leak in
the CH system and so checked all the radiators and pipes in the house
but couldn't see any evidence of this. The only pipes I can't check
are those under the downstairs floorboards. I would expect to see damp
patches in the ceiling if pipes between the floors were leaking.
Besides, if there was a leak in the CH system then surely this would
result in the highest radiators (in the loft) having "cold patches"
where air had replaced the lost water. This is not the case, in fact,
I have bled all radiators and none had any significant amount of air in
them. Does this suggest that the CH system is NOT leaking and that the
problem is definately with the boiler?
We have already had an engineer replace a part last week (after waiting
for 2 weeks for the replacement part to arrive) but this hasn't made
the slightest bit of difference. Sorry, but I don't know what part he
changed!
Are there any more tests I can perform to try to confirm that this is
definately a boiler problem and not caused by leaking radiators/pipes?
The boiler is covered by an insurance policy, but the radiators and
pipes aren't so I want to make sure that the engineer doesn't try to
blame a leaking system for the fault rather than a faulty boiler on his
next visit.
If it is the boiler, any idea what might be causing it?
Thanks.
Try the SealedCH FAQ. It's the expansion vessel for sure.
--
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