I have a pressurised CH combi boiler, the system pressure has gone up by
around 2 bar over the last few weeks.

Bleeding the radiators reveals pale water that seems to have some tiny air
bubbles.

Any ideas what's causing this? And can I just keep bleeding to get the
pressure down? The boiler hasn't minded working at 3.5bar or so, so far.

Thanks.

Bart

I have a pressurised CH combi boiler, the system pressure has gone up by
around 2 bar over the last few weeks.

Most likely either a not disconnected filling loop that is passing water
(you hope) or a leak in the combi water to water heat exchanger (you hope
not). An outside chance of a dodgy pressure gauge.

Christian.

Bart C wrote:

I have a pressurised CH combi boiler, the system pressure has gone up by
around 2 bar over the last few weeks.

Bleeding the radiators reveals pale water that seems to have some tiny air
bubbles.

Any ideas what's causing this? And can I just keep bleeding to get the
pressure down? The boiler hasn't minded working at 3.5bar or so, so far.

The problem will be that the pressure release valve will open shortly,
and these don't always reseal correctly. You then have a drip outside.
Also it suggests you are continously introducing fresh (i.e. oxygenated)
water into the system that will dilute the inhibitor and cause corrosian.

Is the filling loop still attached to the pipework? If so remove this
and check the filling tap is not letting by a constant trickle of water.

If this is not the case, then the only place where the domestic hot
water and the heating system water come close to each other is in the
plate heat exchanger in the boiler. If this had a pinhole leak between
primary and secondary sides it could also cause your problem.

(this all assumes you don't have a pressurised stored hot water cylinder
run from the heating side of the combi)

--
Cheers,

John.

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"John Rumm" wrote in message
...
Bart C wrote:

I have a pressurised CH combi boiler, the system pressure has gone up by
around 2 bar over the last few weeks.

Bleeding the radiators reveals pale water that seems to have some tiny
air bubbles.

Any ideas what's causing this? And can I just keep bleeding to get the
pressure down? The boiler hasn't minded working at 3.5bar or so, so far.

The problem will be that the pressure release valve will open shortly, and
these don't always reseal correctly. You then have a drip outside. Also it
suggests you are continously introducing fresh (i.e. oxygenated) water
into the system that will dilute the inhibitor and cause corrosian.

Is the filling loop still attached to the pipework? If so remove this and
check the filling tap is not letting by a constant trickle of water.

Disconnected this and there is a leak from the inlet service valve of about
1 drop every 10-15 seconds.

If that's the cause then it's amazing such an innocuous looking drip should
pressurise my CH system.

Thanks for both your replies.

Bart

In an earlier contribution to this discussion,
Bart C wrote:


Disconnected this and there is a leak from the inlet service valve of
about 1 drop every 10-15 seconds.

If that's the cause then it's amazing such an innocuous looking drip
should pressurise my CH system.

Yes, but think about it. Four or five drops per minute - how many litres is
that is several weeks? Introducing that amount of extra water will
*certainly* pressurise it!
--
Cheers,
Roger
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Roger Mills wrote:
In an earlier contribution to this discussion,
Bart C wrote:


Disconnected this and there is a leak from the inlet service valve of
about 1 drop every 10-15 seconds.

If that's the cause then it's amazing such an innocuous looking drip
should pressurise my CH system.

Yes, but think about it. Four or five drops per minute - how many litres is
that is several weeks? Introducing that amount of extra water will
*certainly* pressurise it!
--

It's not really that many drops entering the system over a period of
time more that the pressure in the two systems will try to equate over
a period of time. If the mains is the same pressure as the "sealed"
system then no water will enter. The reason the filling loop *must* be
disconnected in the opposite problem - if the mains pressure drops
water from your boiler system could be introduced into the mains water.

wrote:

It's not really that many drops entering the system over a period of
time more that the pressure in the two systems will try to equate over
a period of time. If the mains is the same pressure as the "sealed"

Unlikely I would ahve thought. Most combis will have the blow off valve
set at between 3 and 3.5 bar. Mains water will frequently be more than
that.

system then no water will enter. The reason the filling loop *must* be
disconnected in the opposite problem - if the mains pressure drops
water from your boiler system could be introduced into the mains water.

That is also the reason there must be a double check valve fitted to the
heating circuit so that water can not escape from it even if the tap
were open and the mains pressure dropped below the system pressure.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In an earlier contribution to this discussion,
John Rumm wrote:

wrote:

It's not really that many drops entering the system over a period of
time more that the pressure in the two systems will try to equate
over a period of time. If the mains is the same pressure as the
"sealed"

Unlikely I would ahve thought. Most combis will have the blow off
valve set at between 3 and 3.5 bar. Mains water will frequently be
more than that.


"Try to equate" is correct. It will take a long time at a very small flow
rate, and the safety valve will operate before it actually gets there. From
what the OP said, it was getting that way before he decided to do something
about it!
--
Cheers,
Roger
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