No, I haven't gone and bought a combi :-)

A friend has a Worcester 240 combi boiler, about 9 years old. The
pressure started dropping a week ago, and it now needs topping up
several times a day. Further investigation reveals that it is losing
water from the drain that goes to the outside of the house. This isn't a
condensing boiler.

I have zero experience with combis. Any pointer to what this might be,
where to start, etc.? What is this drain? Why is it there? What does it
connect to? What could be causing the water loss?


TIA


--
Grunff

"Grunff" wrote in message
...
No, I haven't gone and bought a combi :-)

A friend has a Worcester 240 combi boiler, about 9 years old. The pressure
started dropping a week ago, and it now needs topping up several times a
day. Further investigation reveals that it is losing water from the drain
that goes to the outside of the house. This isn't a condensing boiler.

I have zero experience with combis. Any pointer to what this might be,
where to start, etc.? What is this drain? Why is it there? What does it
connect to? What could be causing the water loss?


TIA


--
Grunff

Must be the pressure relief valve surely? Perhaps it's got a bit of grit
stuck in it?

Alex

"Grunff" wrote
| No, I haven't gone and bought a combi :-)
| A friend has a Worcester 240 combi boiler, about 9 years old.
| The pressure started dropping a week ago, and it now needs
| topping up several times a day. Further investigation reveals
| that it is losing water from the drain that goes to the outside
| of the house. This isn't a condensing boiler.

The 'drain' should be copper pipe, turned back against the wall. It is the
outlet of the pressure relief valve and squirts out boiling water.

| I have zero experience with combis. Any pointer to what this
| might be, where to start, etc.? What is this drain? Why is it
| there? What does it connect to? What could be causing the water loss?

The pressure valve is opening and releasing water. If the system is within
pressure (check gauge on boiler) the valve is faulty. If the system is over
pressure then the pressure vessel (which may be within the boiler or
elsewhere) is failing.

Owain

"Alex (YMG)" wrote in message
...
"Grunff" wrote in message
...
No, I haven't gone and bought a combi :-)

A friend has a Worcester 240 combi boiler, about 9 years old. The
pressure
started dropping a week ago, and it now needs topping up several times a
day. Further investigation reveals that it is losing water from the
drain
that goes to the outside of the house. This isn't a condensing boiler.

I have zero experience with combis. Any pointer to what this might be,
where to start, etc.? What is this drain? Why is it there? What does it
connect to? What could be causing the water loss?

The pressure relief valve will blow off at 2.5 - 3 bar. The pressure of a
normal system is somewhere in the 1.5 bar region. To prevent a large
pressure increase in the system when the combi fires up the CH, there is a
bladder-like air-sac in a big metal doughnut thingy. This is an expansion
reservoir that takes up the expansion of water in the system as it heats up,
thereby stopping the system pressure climbing to dangerous levels. Your
friend's air reservoir ( I forget the proper name for the item ) either has
lost all its air via the top-up bicycle valve which is attached to the
doughnut, or has a punctured diaphragm inside and has lost all its air into
the CH system. Thus, when the CH fires up, the CH water expands, the system
pressure rises too far and the last-ditch safety feature, the blow-off
valve, does its stuff.

You would probably do best to locate the expansion reservoir doughnut (
possibly painted red, at the back of the combi, about a foot across??? ),
and see if you can pump it up via the bicycle repressurising valve. Then
keep an eye on the system pressure, maybe for several weeks. If the system
loses the ability to regulate pressure again, then it'll probably need a new
expansion reservoir, 'cause the daphragm will be leaking.

Andy.

andrewpreece wrote:


You would probably do best to locate the expansion reservoir doughnut (
possibly painted red, at the back of the combi, about a foot across??? ),
and see if you can pump it up via the bicycle repressurising valve. Then
keep an eye on the system pressure, maybe for several weeks. If the system
loses the ability to regulate pressure again, then it'll probably need a new
expansion reservoir, 'cause the daphragm will be leaking.

And if the diaphragm is totally buggered, when you push the pin on the
Schrader valve water will **** out, right? And this means there is no
expansion space, so the pressure relief valve blows every time the
boiler fires. Got it. We need a new expansion reservoir. Many thanks for
the detailed explanation.


--
Grunff

Grunff wrote:

And if the diaphragm is totally buggered, when you push the pin on the
Schrader valve water will **** out, right? And this means there is no
expansion space, so the pressure relief valve blows every time the
boiler fires. Got it. We need a new expansion reservoir. Many thanks for
the detailed explanation.

If it is the diaphram, you may find it simpler to just add another
expansion chamber elsewhere, rather than trying to get at the original one.

--
Cheers,

John.

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

Check that the orange expansion vessel is working correctly. Undo Schraeder valve (bike pump nipple) and move needle asside briefly, is air let out or water? Water? get a new expansion vessel. Air? Check pressure with car pressure guage. To do this, let all pressure out of heating system darin down until pressure guage on boiler reads 0, stop there. What is pressure at Schraeder valve? 0.5 to 1 bar? OK Less? Pump it up with a bike pump.

Refill, get heating water jolly hot, turn off and blow it all out of the prv. The hot water jetting out may just clean the seat, but probably won't. If it doesn't work, buy a new prv. To fit, drain boiler (through prv) after isolating flow and return pipes, fit new prv, re-open valves and top up.

Job's a goodun.

Great combi by the way, wish Worcester were still that good.

John Rumm wrote:

Grunff wrote:

And if the diaphragm is totally buggered, when you push the pin on the
Schrader valve water will **** out, right? And this means there is no
expansion space, so the pressure relief valve blows every time the
boiler fires. Got it. We need a new expansion reservoir. Many thanks for
the detailed explanation.

If it is the diaphram, you may find it simpler to just add another
expansion chamber elsewhere, rather than trying to get at the original one.

Could you explain that a little further? How would one do that?

Cheers - Greg

Greg C wrote:

If it is the diaphram, you may find it simpler to just add another
expansion chamber elsewhere, rather than trying to get at the original one.


Could you explain that a little further? How would one do that?

You can buy expansion vessels pretty cheaply on their own (as you would
need to if you converting a regular vented heating system into a sealed
system for example).

Something like the 12L one here, ought to be more than adequate for a
good proportion of systems.

http://www.bes.ltd.uk/products/109.asp

The actual size you need will depend on the volume of water in the
system. The following guideline figures come from Ideal's documentation,
but should apply to any sealed system:

Assuming pre charge pressure between 0.5 and 0.75 bar

System volume Expansion vessel
(litres) volume (litres)
25 1.8
50 3.7
75 5.5
100 7.4
125 9.2
150 11.0
175 12.9
190 14.0
200 14.7
250 18.4
300 22.1
For other system volumes
multiply by the factor across 0.074

If the vessel is too small then you will still get the over pressure
symptom described by the OP, however it does not matter if it is larger
than required.

The expansion vessel can be installed anywhere on the system as long as
it never gets gated off by zone valves etc. Note however that some
boiler makers do specify preferred locations for expansion vessels.

Installation is typically just a case of tee'ing into the heating loop
pipework and fitting the vessel to the tee (having pumped it up to half
to three quaters of a bar pressure).

Lots more on this subject in the sealed system FAQ:

http://www.makewrite.demon.co.uk/SealedCH.html


--
Cheers,

John.

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

On Mon, 07 Feb 2005 00:44:24 +0000, John Rumm wrote:



Installation is typically just a case of tee'ing into the heating loop
pipework and fitting the vessel to the tee (having pumped it up to half
to three quaters of a bar pressure).

IME you have to let them down to the pressure you want. They are usually
pre-charged to at least 3 bar.


--
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