I have a Ravenheat combi boiler which is now losing pressure after use
everyday. The pressure is not lost instantly, but the day after the
pressure has dropped to zero.

Filling the system takes no time to reach 1.5 bar. I have checked all
the rads for any air in the system and found that all were filled to
the top.

This leads me to believe that the leak is not in the pipework but with
the boiler, any idea's what could be causing this recurrent problem??

Any help/advice greatly appreciated.

Thanks
Naz

In message .com, nazn
writes
I have a Ravenheat combi boiler which is now losing pressure after use
everyday. The pressure is not lost instantly, but the day after the
pressure has dropped to zero.

Filling the system takes no time to reach 1.5 bar. I have checked all
the rads for any air in the system and found that all were filled to
the top.

This leads me to believe that the leak is not in the pipework but with
the boiler, any idea's what could be causing this recurrent problem??

It sounds like there might be problem with the pressure vessel/
diaphragm. The pressure vessel is hard to access, being behind the
boiler (least ways mine was)

I believe the normal solution is fit a new pressure vessel elsewhere on
the system.
--
Chris French

In an earlier contribution to this discussion,
nazn wrote:

I have a Ravenheat combi boiler which is now losing pressure after use
everyday. The pressure is not lost instantly, but the day after the
pressure has dropped to zero.

Filling the system takes no time to reach 1.5 bar. I have checked all
the rads for any air in the system and found that all were filled to
the top.

This leads me to believe that the leak is not in the pipework but with
the boiler, any idea's what could be causing this recurrent problem??

Any help/advice greatly appreciated.

Thanks
Naz

Sounds like you've got a problem with the pressure vessel. This may be a
bomb-shaped thing located somewhere on the pipework, or it may be inside the
boiler casing - in which case is it more likely to be pancake shaped. Either
way, it should have a Schrader valve (like a car tyre valve) for
pressurising it with air. With the water system unpressurised, the air
pressure in the expansion vessel should be about 0.7 bar (10 PSI). Measure
this with a car tyre pressure gauge, and top up if necessary. If water comes
out of the valve, the internal diaphragm is shot - and you'll need to
replace the vessel.

When the vessel has insufficient air in it, it cannot provide a spring to
cater for expansion. So you pressurise the water system cold, the water
expands when the system gets hot, and gets expelled through the safety valve
rather than going into the expansion vessel. Then when it cools, the
pressure drops. I suspect that this is what you are seeing.
--
Cheers,
Set Square
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nazn wrote:

Any help/advice greatly appreciated.

What the others said! ;-)

If you need a quick fix then deliberately allow some air into one of
your radiators - that will then give the system some expansion room. You
don't need a huge amount since you are only talking about a few litres
of expansion for every 100 litres of system water capacity.

--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
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Thanks for all the replies,

The boiler has a tyre valve type unit on the top of the boiler, I
pressed the valve in using a small screwdriver and had hot water come
out of it (the boiler was running at the time). When you refer to the
pressure vessel, is this the big round (15" inch or so) pancake shape
unit that sits at the back of the unit? if so this sounds like a major
prob!
If the diaphram is a seperate unit I would be interested to hear where
this is located or what it looks like. On the other hand time to call
in a corgi!

Naz

In an earlier contribution to this discussion,
nazn wrote:

Thanks for all the replies,

The boiler has a tyre valve type unit on the top of the boiler, I
pressed the valve in using a small screwdriver and had hot water come
out of it (the boiler was running at the time). When you refer to the
pressure vessel, is this the big round (15" inch or so) pancake shape
unit that sits at the back of the unit? if so this sounds like a major
prob!

Yes, that's the pressure vessel. the diaphragm is inside and separates -
rather *should* separate - the water from the air. Clearly, yours is shot
since water is getting to where only air should be.

If the diaphram is a seperate unit I would be interested to hear where
this is located or what it looks like. On the other hand time to call
in a corgi!

Naz

You can't replace the diaphragm - you have to replace the whole pressure
vessel. As someone else noted recently - either in this or a similar
thread - you can simply abandon the pressure vessel inside the boiler and
install another one elsewhere in the system if that's easier. [Make sure the
valve cap is firmly replaced on the abandoned one]. It's not really a Corgi
job per se - just straightforward plumbing - since it's connected to the
water pipes - not the gas pipes.
--
Cheers,
Set Square
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In message .com, nazn
writes
Thanks for all the replies,

The boiler has a tyre valve type unit on the top of the boiler, I
pressed the valve in using a small screwdriver and had hot water come
out of it (the boiler was running at the time).

If it's the same as my Ravenheat (in our old house) this is automatic
air release valve IIRC (to stop air collecting at the top of the boiler
- like bleeding a rad) nothing to do with the pressure vessel.

When you refer to the
pressure vessel, is this the big round (15" inch or so) pancake shape
unit that sits at the back of the unit? if so this sounds like a major
prob!

Yep that's it.

If the diaphram is a seperate unit I would be interested to hear where
this is located or what it looks like. On the other hand time to call
in a corgi!

The diaphragm is in the pressure vessel - basically across the middle it
has air on one side, and the system water on the other, this is
pressurized (by letting in mains water normally) to then pressurize the
system. If this leaks then of course you can't pressurize the system.

however, as others have said you should potentially be able to
re-pressurize this, though I don't know how accessible it is, you boiler
manual should give instructions on this if possible.
--
Chris French

nazn wrote:

If the diaphram is a seperate unit I would be interested to hear where
this is located or what it looks like. On the other hand time to call
in a corgi!

Have a look at part number 11351 on:

http://www.bes.ltd.uk/

You can find any suitable place on the system to install one of these -
probably simpler than going through the hassle of getting the correct
replacement part for the boiler and fitting it.

--
Cheers,

John.

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

Thank you John for the information you have provided, I have looked up
the part and am seriously considering this option, however before I go
down this road, I would like to attempt to let air in one of the
radiators, as a temporary solution. Any idea's how one would go
around doing this?

As for the expansion vessel install would I need to isolate the
existing unit? If this is the case this sounds tricky

In message . com, nazn
writes
Thank you John for the information you have provided, I have looked up
the part and am seriously considering this option, however before I go
down this road, I would like to attempt to let air in one of the
radiators, as a temporary solution. Any idea's how one would go
around doing this?

Drain down the system a bit, letting air into the rad. Refill but don't
bleed one rad (or not fully anyway).

As for the expansion vessel install would I need to isolate the
existing unit? If this is the case this sounds tricky

Don't imagine so.
--
Chris French

chris French wrote:

Drain down the system a bit, letting air into the rad. Refill but don't
bleed one rad (or not fully anyway).

Yup that would work. As would: turn off the valves on both sides of an
upstairs rad. Place a tray under it, and open one of the connections
between valve and radiator a little to allow water to leak out. Open the
vent on the rad to let air in. Once you have a say 5L out do up the tail
and the air vent again and reopen the valves.

(make a note of how many turns were required for the lockshield valve
when closing so that you can get the same position when opening it again)


--
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:


Yup that would work. As would: turn off the valves on both sides of an
upstairs rad. Place a tray under it, and open one of the connections
between valve and radiator a little to allow water to leak out. Open
the vent on the rad to let air in. Once you have a say 5L out do up
the tail and the air vent again and reopen the valves.

(make a note of how many turns were required for the lockshield valve
when closing so that you can get the same position when opening it
again)

I can see where you're coming from with the bit in brackets, but I'm not
sure of the validity of restoring a half-empty radiator to the same balance
position as was needed when it was full.
--
Cheers,
Set Square
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In message , Set Square
writes
In an earlier contribution to this discussion,
John Rumm wrote:

(make a note of how many turns were required for the lockshield valve
when closing so that you can get the same position when opening it
again)

I can see where you're coming from with the bit in brackets, but I'm not
sure of the validity of restoring a half-empty radiator to the same balance
position as was needed when it was full.

but you'll need to know anyway once the pressure vessle problem was
sorted and things were back to normal.
--
Chris French

In an earlier contribution to this discussion,
chris French wrote:

In message , Set Square
writes
In an earlier contribution to this discussion,
John Rumm wrote:

(make a note of how many turns were required for the lockshield
valve when closing so that you can get the same position when
opening it again)

I can see where you're coming from with the bit in brackets, but I'm
not sure of the validity of restoring a half-empty radiator to the
same balance position as was needed when it was full.

but you'll need to know anyway once the pressure vessle problem was
sorted and things were back to normal.

That's true! Meanwhile, you'll probably need it wider open.
--
Cheers,
Set Square
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