My sealed CH system appears to be playing up, although is still heating
the water (tank) and the rads.

I noticed that the pressure guage on the boiler dropped to zero
yesterday when the main room themostat reached the temp limit. Prior
to that the pressure had been at around 2.5-3 bar. Last night I shut
it all off and the pressure settled at 1 bar. I turned everything back
on and this time when the thermostat clicked off the pressure settled
back to 1 again.

But this morning it clicked off and dropped back to 0.5bar.

Anyone got any ideas what I should check? I don't know much about the
setup, but it has got 2 zone valves under the HW tank (one of which the
BGas engineer changed recently)

On 5 Oct 2005 02:33:41 -0700, "Alan" wrote:

My sealed CH system appears to be playing up, although is still heating
the water (tank) and the rads.

I noticed that the pressure guage on the boiler dropped to zero
yesterday when the main room themostat reached the temp limit. Prior
to that the pressure had been at around 2.5-3 bar. Last night I shut
it all off and the pressure settled at 1 bar. I turned everything back
on and this time when the thermostat clicked off the pressure settled
back to 1 again.

But this morning it clicked off and dropped back to 0.5bar.

Anyone got any ideas what I should check? I don't know much about the
setup, but it has got 2 zone valves under the HW tank (one of which the
BGas engineer changed recently)

I'd check the expansion vessel first. An operating pressure of 2.5-3 bar is
too high for most systems. You'll need to locate the vessel (often in the
boiler casing), and then release water from the system so that the boiler
gauge drops to 0. If you put a tyre pressure gauge on the expansion vessel
valve, it should be around 1 bar (iirc). If not, pump it up. If it holds
pressure, then it has just gone down slowly over the years (using Schrader
valves pretty much guarantees this in time). Then refill the system to the
correct pressure on the boiler gauge (1 bar plus natural head on mine). If
your vessel won't hold pressure, it will need to be replaced as the internal
diaphragm is shot.

Without an effective expansion vessel, your system is "full" of water and
any temperature rise produces large pressure rises. The expansion vessel is
there to provide a "cushion", when it's working properly, that is.

I'm at a loss to explain the variation in non-running pressure, though.

--
Aging is bad, but consider the alternative.

Thanks John, The tank/piping in my airing cupboard looks like this
pictu
http://www.diydoctor.org.uk/projects...s.htm#Unvented
system: (sealed system)

Would this expansion vessel be the one I need to check (or is there
another in the boiler casing, boiler is an Ideal Classic). I did point
out the high pressure to the BGas man, but he said it was ok. It
wasn't dropping to zero at this point in time though.

Could the gauge be faulty?

And I checked the tundish yesterday, there was no sign of it having
been wet recently (and in fact in was coated in dust on the inside.)

In an earlier contribution to this discussion,
Alan wrote:

Thanks John, The tank/piping in my airing cupboard looks like this
pictu

http://www.diydoctor.org.uk/projects...s.htm#Unvented
system: (sealed system)

Would this expansion vessel be the one I need to check

NO! Not if your airing cupboard looks like the one in the diagram. This
shows an unvented (mains pressure) hot water system - whereas your problem
is in the *primary* circulation system - i.e. the water which circulates
from the boiler, through the internal coil in the hot cylinder, and through
the radiators.


(or is there
another in the boiler casing, boiler is an Ideal Classic). I did
point out the high pressure to the BGas man, but he said it was ok.
It wasn't dropping to zero at this point in time though.

If it's a sealed primary system, there'll be another one somewhere. It may
be spherical or - if it's inside the boiler casing - it could look like a
large fat pancake.

Could the gauge be faulty?

It's possible. Usually, if the pressure genuinely fluctuates by too much,
water is lost through the safety valve - and when the system cools, the
pressure then goes to zero.

With the primary circuit de-pressurised, the gas in the expansion vessel
should be at about 0.7bar (10psi) as measured at the Schrader valve. If it's
less than this, pump it up with a car tyre pump. Then use the filling loop
to pressurise the wet primary system to about 1bar when cold. When the
system gets hot, the pressure should rise to about 2bar. If it goes
significantly higher than this, you have a problem. The safety valve is
designed to operate at 3bar - but you *don't* want that to happen!
--
Cheers,
Set Square
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On 5 Oct 2005 04:32:01 -0700, "Alan" wrote:

Thanks John, The tank/piping in my airing cupboard looks like this
pictu
http://www.diydoctor.org.uk/projects...s.htm#Unvented
system: (sealed system)

Would this expansion vessel be the one I need to check (or is there
another in the boiler casing, boiler is an Ideal Classic). I did point
out the high pressure to the BGas man, but he said it was ok. It
wasn't dropping to zero at this point in time though.

Could the gauge be faulty?

See Set Square's response. I would note that the expansion vessel in my
boiler is actually hanging on the back of it, nearest the wall, and can be
seen without removing any panels. It's a large, red, pancake thing :-)

They can be completely external, however.

--
The knuckles! The horrible knuckles!

The weirdest things happen. I found the red flat pancake thing under
the top cover on the boiler, along with a valve with a wire going to
the pressure gauge - I had a poke around, but I didn't touch anything
switch/button like. I checked upstairs in the airing cupboard, no sign
of leaks, and the expansion vessel upstairs didn't look like it had
been touched in ages (covered in dust), didn't see a valve (although
there must have been one somewhere).

The boiler was burning away, pressure was approaching 3bar again - I
went outside to check the pressure relief pipe, which appeared to have
been dripping at some point (slightly wet). Went back in and the
boiler pressure had dropped to 1 bar and the heating was off (boiler
themostat). I adjusted the boiler themostat, which kicked the boiler
back in, turned it down, it cut out as expected. At this point I
noticed an 'orange' glowing light from the control board, which I don't
remember seeing before but I might have just missed it.

Anyway, the boiler now appears to be ok - cold pressure settles at 1
bar, running pressure is just above 1.5 bar. I have no idea what
happened, maybe poking around (and moving the cover) fixed something,
or there was a blockage somewhere that's now gone. The pump now
appears to run once the boiler themostat cuts out, which I definitely
couldn't hear before (and neither could the BGas man the other week).
Perhaps I've got a faulty control board?

I wish I had a nice simple heating system!

Thanks for the help.

Alan.

In an earlier contribution to this discussion,
Alan wrote:


Anyway, the boiler now appears to be ok - cold pressure settles at 1
bar, running pressure is just above 1.5 bar.

That sounds about right.

I have no idea what
happened, maybe poking around (and moving the cover) fixed something,
or there was a blockage somewhere that's now gone.

Unlikely! Someone else has asked a very valid question about the filling
loop being left connected - which may explain things if it is.


The pump now
appears to run once the boiler themostat cuts out, which I definitely
couldn't hear before (and neither could the BGas man the other week).
Perhaps I've got a faulty control board?

Does the pump run for ever, or only for a short time after the boiler stops?
If the latter, this is intentional - to carry the residual heat away and
stop the boiler from overheating.
--
Cheers,
Set Square
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The filling loop, at least the one in the airing cupboard, which is the
only one afaik and does affect the pressure gauge, is permanently
connected by the look of it. I've never tried to remove it, and the 2
BGas engineers that looked at the system didn't comment on the fact it
was. I'll check if it has got a leak.

The pump only runs until the room themostat cuts out, which also cuts
off the boiler if it was burning. I can definitely hear it running
now, which I couldn't before when the boiler stopped burning.

Hopefully it's ok, I'll check the filling loop and pressure relief pipe
again tonight.

In an earlier contribution to this discussion,
Alan wrote:

The pump only runs until the room themostat cuts out, which also cuts
off the boiler if it was burning. I can definitely hear it running
now, which I couldn't before when the boiler stopped burning.

That's ok - that's how it should be.

Hopefully it's ok, I'll check the filling loop and pressure relief
pipe again tonight.

The filling loop *must* be disconnected after use. Otherwise, any leakge
through its valves can over-pressurise the system from the mains.
--
Cheers,
Set Square
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On Thu, 6 Oct 2005 20:32:31 +0100, "Set Square" wrote:

The filling loop *must* be disconnected after use.

Care to put a figure on the percentage that actually are, though ?

Otherwise, any leakge
through its valves can over-pressurise the system from the mains.

The system over-pressure valve would presumably have to fail for damage to
occur, though. So that's three valve failures before real problems arise.

[Besides, I think I might rather that a faulty filling-loop valve leaked
into my CH system as opposed to leaking all over my house, having seen the
damage done by an uncontrolled burst on a mains cold-water system.]

--
Tourist, Rincewind decided, meant "idiot".