Two days ago I found all the towels in the airing cupboard were very
damp, and came to the conclusion that the only place this water could
have come from is splashing from the tundish on the pressure relief
valve of my unvented HW cyclinder. Judging by the amount of 'splashed'
water, the amount that must have gone down the overflow pipe must have
been substantial.

If I'm right, and something caused the cylinder to over-pressurise, this
is obviously a serioud concern and I know I need to get it looked at ASAP.

I've been watching out for a repeat performance, to confirm the source
of the water and to find the conditions under which it happened, in
order to help with diagnostics, as I don't want to get a plumber in who
will just condemn the whole system due to inability to localise the
problem, However, it hasn't happened again (yet at least).

Can anyone suggest what might cause this? and whether in fact there's
likely to be something obvious that a plumber could home in on?

The system has been in for about 10 years with no problems up to now.

Thanks
David

On Jan 20, 9:02 pm, Lobster wrote:
Two days ago I found all the towels in the airing cupboard were very
damp, and came to the conclusion that the only place this water could
have come from is splashing from the tundish on the pressure relief
valve of my unvented HW cyclinder.

In NZ, HW cylinders are probably different
However my pressure relief valve started leaking, and this was caused
by the spring inside having rusted and collapsed after 20 years of
sitting in a pool of water. The instructions for mounting the valve do
not say to mount the valve vertical with the drain underneath so that
the spring is not sitting in water. I suppose I should complain to the
manufacturer.

Of course there is always some hot water overflowing whenever cold
water introduced to the HW cylinder expands. Apparently this is
acceptable to the experts. But not to me.

On Thu, 20 Jan 2011 08:02:11 +0000
Lobster wrote:

Two days ago I found all the towels in the airing cupboard were very
damp, and came to the conclusion that the only place this water could
have come from is splashing from the tundish on the pressure relief
valve of my unvented HW cyclinder. Judging by the amount of
'splashed' water, the amount that must have gone down the overflow
pipe must have been substantial.

If I'm right, and something caused the cylinder to over-pressurise,
this is obviously a serioud concern and I know I need to get it
looked at ASAP.

I've been watching out for a repeat performance, to confirm the
source of the water and to find the conditions under which it
happened, in order to help with diagnostics, as I don't want to get a
plumber in who will just condemn the whole system due to inability to
localise the problem, However, it hasn't happened again (yet at
least).

Can anyone suggest what might cause this? and whether in fact there's
likely to be something obvious that a plumber could home in on?

The system has been in for about 10 years with no problems up to now.

Thanks
David

How is the pressure in the system managed? There seem to be two
systems (that I've seen), in one the unvented cylinder has an external
diaphragm-type expansion box as used in sealed HW systems, in others,
like my OSO, the shape of the cylinder top has an air space who allows
for expansion without a diaphragm. If it's like my OSO, there is a
documented procedure for re-installing the air gap (which involves some
draining down). A diaphragm type might have a split diaphragm - 10
years?

It might be that the air gap has reformed naturally from dissolved gas
in the water feed, of course. When the pressure valve releases, they
often go with a bang, especially if they have not opened recently.

R.

On Jan 20, 8:02*am, Lobster wrote:

There should be two valves discharging into the tundish, a PRV and a
T&PRV.

Either one of them is working as intended, indicating a fault, OR one
of them is defective.

The T&PRV will start to discharge at a reduced temperature if it
becomes defective; I'd first suspect that. You need to stand and watch
as the cylinder heats up.

It could otherwise be a defective pressure reducing valve, a deflated/
broken expansion vessel (or airgap depleted, depending on the model),
defective PRV, or something I haven't thought of.

The T&PRV will discharge hot/warm water, the PRV will discharge cold.

On Jan 20, 8:13*am, Matty F wrote:
Of course there is always some hot water overflowing whenever cold
water introduced to the HW cylinder expands. Apparently this is
acceptable to the experts. But not to me.

The UK Water Regulations prohibit such waste of water, so UK unvented
water heaters have an expansion vessel or an airgap inside the
cylinder to accomodate the expansion of the heated water. If the
expansion vessel/air gap fails, you get water discharged as you
describe. The rest of the world manages without expansion vessels.

On Jan 20, 10:13*am, Onetap wrote:
On Jan 20, 8:02*am, Lobster wrote:

There should be two valves discharging into the tundish, a PRV and *a
T&PRV.

....there could also be a third - the PRV for the central heating
system (in which case, again, it could be a defective PRV or expansion
vessel).

Mathew

On Jan 20, 12:05*pm, Mathew Newton wrote:
...there could also be a third - the PRV for the central heating
system (in which case, again, it could be a defective PRV or expansion
vessel).

That one should terminate outside. The tundish supplied with the UVHW
kit of parts has connections only for the two UVWH PRV discharges.

I thought it might be the T&PRV because I fixed one on which the owner
'found all the towels in the airing cupboard were very damp, and came
to the conclusion etc......). It was an unoccupied buy-to-let
property & the T&PRV discharged when the water temperature reached
about 45 to 55 degC. There was no splashing on it discharging, all the
damp was due to steam condensing on the uninsulated cold water pipes
and so it appeared that the 'leak' was nowhere near the tundish.

The T&PRV manufacturers said they'd never heard of such a thing
happening before; lying *******s.

On Jan 20, 8:13*am, Matty F wrote:
On Jan 20, 9:02 pm, Lobster wrote:

Two days ago I found all the towels in the airing cupboard were very
damp, and came to the conclusion that the only place this water could
have come from is splashing from the tundish on the pressure relief
valve of my unvented HW cyclinder.

In NZ, HW cylinders are probably different
However my pressure relief valve started leaking, and this was caused
by the spring inside having rusted and collapsed after 20 years of
sitting in a pool of water. The instructions for mounting the valve do
not say to mount the valve vertical with the drain underneath so that
the spring is not sitting in water. I suppose I should complain to the
manufacturer.

Of course there is always some hot water overflowing whenever cold
water introduced to the HW cylinder expands. Apparently this is
acceptable to the experts. But not to me.

An expansion vessl prevents this. If you have one and it isn't, it
needs air puming in or a new vessel.

On Jan 20, 10:13*am, Onetap wrote:
On Jan 20, 8:02*am, Lobster wrote:

There should be two valves discharging into the tundish, a PRV and *a
T&PRV.

Either one of them is working as intended, indicating a fault, OR one
of them is defective.

The T&PRV will start to discharge at a reduced temperature if it
becomes defective; I'd first suspect that. You need to stand and watch
as the cylinder heats up.

It could otherwise be a defective pressure reducing valve, a deflated/
broken expansion vessel (or airgap depleted, depending on the model),
defective PRV, or something I haven't thought of.

The T&PRV will discharge hot/warm water, the PRV will discharge cold.

Very often the check valve, PRV, over temperature/ pressure valve are
all combined into the one housing these days and there is only one
discharge pipe

On 20/01/2011 08:02, Lobster wrote:
Two days ago I found all the towels in the airing cupboard were very
damp, and came to the conclusion that the only place this water could
have come from is splashing from the tundish on the pressure relief
valve of my unvented HW cyclinder. Judging by the amount of 'splashed'
water, the amount that must have gone down the overflow pipe must have
been substantial.

If I'm right, and something caused the cylinder to over-pressurise, this
is obviously a serioud concern and I know I need to get it looked at ASAP.

I've been watching out for a repeat performance, to confirm the source
of the water and to find the conditions under which it happened, in
order to help with diagnostics, as I don't want to get a plumber in who
will just condemn the whole system due to inability to localise the
problem, However, it hasn't happened again (yet at least).

Can anyone suggest what might cause this? and whether in fact there's
likely to be something obvious that a plumber could home in on?

The system has been in for about 10 years with no problems up to now.

Thanks
David

The expansion vessel has lost it's air volume.

What make / model of cylinder is it?

On some models, ( eg Heatrae Sadia Megaflo )this is an internal air
volume that can be re-generated by following the instructions on the tank.

Otherwise, the expansion vessel may be external.
This has either lost pressure and needs to be pumped up, or has ruptured
internally and needs replaced.

--
Ron

On 20/01/2011 18:28, Ron Lowe wrote:
On 20/01/2011 08:02, Lobster wrote:
Two days ago I found all the towels in the airing cupboard were very
damp, and came to the conclusion that the only place this water could
have come from is splashing from the tundish on the pressure relief
valve of my unvented HW cyclinder. Judging by the amount of 'splashed'
water, the amount that must have gone down the overflow pipe must have
been substantial.

If I'm right, and something caused the cylinder to over-pressurise, this
is obviously a serioud concern and I know I need to get it looked at
ASAP.

I've been watching out for a repeat performance, to confirm the source
of the water and to find the conditions under which it happened, in
order to help with diagnostics, as I don't want to get a plumber in who
will just condemn the whole system due to inability to localise the
problem, However, it hasn't happened again (yet at least).

Can anyone suggest what might cause this? and whether in fact there's
likely to be something obvious that a plumber could home in on?

The system has been in for about 10 years with no problems up to now.

The expansion vessel has lost it's air volume.

What make / model of cylinder is it?

On some models, ( eg Heatrae Sadia Megaflo )this is an internal air
volume that can be re-generated by following the instructions on the tank.

Otherwise, the expansion vessel may be external.
This has either lost pressure and needs to be pumped up, or has ruptured
internally and needs replaced.

It's a Vaillant Vantage - have found the instructions he
http://www.docstoc.com/docs/4923997/Installation-Instructions-GB-Unvented-hot-water-storage-cylinders-for
(or
http://preview.tinyurl.com/4z76wch

It does have an expansion vessel sitting above the tank - so do we
reckon that just needs replacing, then (looks very straightforward, ie
it just unscrews - is it actually a diy job or are there big safety
implications and I shouldn't touch?). On p14 of the manual it says it
should be 6.0 bar - can i just check the Schraeder valve on top of the
vessel with a car-tyre jobbie, and if it's less than 6 bar, try pumping
it up?

Thanks
David

On 20/01/2011 20:10, Lobster wrote:

The system has been in for about 10 years with no problems up to now.

The expansion vessel has lost it's air volume.

What make / model of cylinder is it?

On some models, ( eg Heatrae Sadia Megaflo )this is an internal air
volume that can be re-generated by following the instructions on the
tank.

Otherwise, the expansion vessel may be external.
This has either lost pressure and needs to be pumped up, or has ruptured
internally and needs replaced.

It's a Vaillant Vantage - have found the instructions he
http://www.docstoc.com/docs/4923997/Installation-Instructions-GB-Unvented-hot-water-storage-cylinders-for
(or
http://preview.tinyurl.com/4z76wch

It does have an expansion vessel sitting above the tank - so do we
reckon that just needs replacing, then (looks very straightforward, ie
it just unscrews - is it actually a diy job or are there big safety
implications and I shouldn't touch?). On p14 of the manual it says it
should be 6.0 bar - can i just check the Schraeder valve on top of the
vessel with a car-tyre jobbie, and if it's less than 6 bar, try pumping
it up?

Thanks
David




Poke a poking impliment into the valve, as if to deflate a car tyre.
If water comes out, it's goosed and needs replacing.
The diaphram has burst.

If air, ( or nothing! ) then yes, you can pump it up.
If it fails to remain pumped up, it's goosed and needs replacing.

Replacing should be a simple job with no issues.

There are no safety implications: if the expansion vessel fails or is
missing, then the cylnder will continue to vent over-pressure through
the relief valve as it has already done.


--
Ron

On 20/01/2011 20:10, Lobster wrote:


It's a Vaillant Vantage - have found the instructions he
http://www.docstoc.com/docs/4923997/Installation-Instructions-GB-Unvented-hot-water-storage-cylinders-for
(or
http://preview.tinyurl.com/4z76wch

It does have an expansion vessel sitting above the tank - so do we
reckon that just needs replacing, then (looks very straightforward, ie
it just unscrews - is it actually a diy job or are there big safety
implications and I shouldn't touch?). On p14 of the manual it says it
should be 6.0 bar - can i just check the Schraeder valve on top of the
vessel with a car-tyre jobbie, and if it's less than 6 bar, try pumping
it up?

Thanks
David



Additional note:

P5 says the pre-charge pressure on the expansion vessel should be 4 bar.

THe 6 bar reference on P14 is the cracking pressure of the Expansion
Relief Valve.

Pump the thing up to 4 bar cold.

--
R

On 20/01/2011 21:23, Ron Lowe wrote:
On 20/01/2011 20:10, Lobster wrote:


It's a Vaillant Vantage - have found the instructions he
http://www.docstoc.com/docs/4923997/Installation-Instructions-GB-Unvented-hot-water-storage-cylinders-for

(or
http://preview.tinyurl.com/4z76wch

It does have an expansion vessel sitting above the tank - so do we
reckon that just needs replacing, then (looks very straightforward, ie
it just unscrews - is it actually a diy job or are there big safety
implications and I shouldn't touch?). On p14 of the manual it says it
should be 6.0 bar - can i just check the Schraeder valve on top of the
vessel with a car-tyre jobbie, and if it's less than 6 bar, try pumping
it up?

Thanks
David



Additional note:

P5 says the pre-charge pressure on the expansion vessel should be 4 bar.

THe 6 bar reference on P14 is the cracking pressure of the Expansion
Relief Valve.

Pump the thing up to 4 bar cold.


.. . . making sure that the 'wet' side isn't under pressure while you do so.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On Jan 20, 1:29*pm, Onetap wrote:
On Jan 20, 12:05*pm, Mathew Newton wrote:

...there could also be a third - the PRV for the central heating
system (in which case, again, it could be a defective PRV or expansion
vessel).

That one should terminate outside.

Are you sure it has to? Mine doesn't and, sticking my neck out here,
being a new-build one would expect it to comply with the regs.

Mathew

On 20/01/2011 21:15, Ron Lowe wrote:
On 20/01/2011 20:10, Lobster wrote:

The system has been in for about 10 years with no problems up to now.

The expansion vessel has lost it's air volume.

What make / model of cylinder is it?

On some models, ( eg Heatrae Sadia Megaflo )this is an internal air
volume that can be re-generated by following the instructions on the
tank.

Otherwise, the expansion vessel may be external.
This has either lost pressure and needs to be pumped up, or has ruptured
internally and needs replaced.

It's a Vaillant Vantage - have found the instructions he
http://www.docstoc.com/docs/4923997/Installation-Instructions-GB-Unvented-hot-water-storage-cylinders-for

(or
http://preview.tinyurl.com/4z76wch

It does have an expansion vessel sitting above the tank - so do we
reckon that just needs replacing, then (looks very straightforward, ie
it just unscrews - is it actually a diy job or are there big safety
implications and I shouldn't touch?). On p14 of the manual it says it
should be 6.0 bar - can i just check the Schraeder valve on top of the
vessel with a car-tyre jobbie, and if it's less than 6 bar, try pumping
it up?

Poke a poking impliment into the valve, as if to deflate a car tyre.
If water comes out, it's goosed and needs replacing.
The diaphram has burst.

If air, ( or nothing! ) then yes, you can pump it up.
If it fails to remain pumped up, it's goosed and needs replacing.

Replacing should be a simple job with no issues.

There are no safety implications: if the expansion vessel fails or is
missing, then the cylnder will continue to vent over-pressure through
the relief valve as it has already done.

Thanks for the responses. Just checked, and upon depressing the
Schraeder valve I'm rewarded with a barely perceptible little fart -
that's it - just enough to know that the valve was actually depressed.
I'll give repressurising a go first but presumably it'll need replacing.

Isn't it a bit odd that my system works though? Have had CH and HW on
all week with no problems at all except apparently for the one
'overflow' issue.

It's going to be fun trying to repressurise - the vessel is about 5 feet
off the ground in the airing cupboard, with nowhere nearby to site a
footpump. Can you get extension hoses for them or something? Google's
no help. Have in the past tried to use my 12V electric inflator in the
house on a mains adaptor, but it wouldn't provide enough current, and I
don't really want to yank the car battery...

David

Lobster wrote:

It's going to be fun trying to repressurise - the vessel is about 5 feet
off the ground in the airing cupboard, with nowhere nearby to site a
footpump. Can you get extension hoses for them or something? Google's
no help. Have in the past tried to use my 12V electric inflator in the
house on a mains adaptor, but it wouldn't provide enough current, and I
don't really want to yank the car battery...

Maybe get one of the fairly cheap jumpstart/ compressor units from
Maplin or Halfrauds?

--
Tciao for Now!

John.

Lobster wrote:

It's going to be fun trying to repressurise - the vessel is about 5 feet
off the ground in the airing cupboard, with nowhere nearby to site a
footpump. Can you get extension hoses for them or something? Google's
no help. Have in the past tried to use my 12V electric inflator in the
house on a mains adaptor, but it wouldn't provide enough current, and I
don't really want to yank the car battery...

Just use the footpump. Brace the pump against the wall or the doorframe
and operate it with your hands.

If you can clip the end of the pump's hose onto the valve, as you can with
a car tyre valve, great. Otherwise it'll just be a trifle more challenging
because one hand will be needed to hold it on. Perhaps you could hang the
pump on the wall/frame from a small nail, or use an assistant to hold the
hose in position. Then you can operate the pump with both hands (one hand
pretending to be your foot, the other pretending to be the wall or ground).

Alternatively it might be possible to go at it with a stepladder and
stand the foot pump on one of its rungs.

It may not be very comfortable, but if you only need to do it every
10 years, then up with it you can surely put.

On 21/01/2011 13:00, John Rumm wrote:
On 20/01/2011 22:12, Roger Mills wrote:
On 20/01/2011 21:23, Ron Lowe wrote:

P5 says the pre-charge pressure on the expansion vessel should be 4 bar.

THe 6 bar reference on P14 is the cracking pressure of the Expansion
Relief Valve.

Pump the thing up to 4 bar cold.


.. . . making sure that the 'wet' side isn't under pressure while you do
so.

which probably means shut off the mains inlet, and open a hot tap...

I assumed I'd need to open a drain cock on the CH to reduce the pressure
to zero, thereby losing all that precious inhibitor - is that not the case?

David

On 21/01/2011 11:58, Ronald Raygun wrote:
Lobster wrote:

It's going to be fun trying to repressurise - the vessel is about 5 feet
off the ground in the airing cupboard, with nowhere nearby to site a
footpump. Can you get extension hoses for them or something? Google's
no help. Have in the past tried to use my 12V electric inflator in the
house on a mains adaptor, but it wouldn't provide enough current, and I
don't really want to yank the car battery...

Just use the footpump. Brace the pump against the wall or the doorframe
and operate it with your hands.

If you can clip the end of the pump's hose onto the valve, as you can with
a car tyre valve, great. Otherwise it'll just be a trifle more challenging
because one hand will be needed to hold it on. Perhaps you could hang the
pump on the wall/frame from a small nail, or use an assistant to hold the
hose in position. Then you can operate the pump with both hands (one hand
pretending to be your foot, the other pretending to be the wall or ground).

Alternatively it might be possible to go at it with a stepladder and
stand the foot pump on one of its rungs.

It may not be very comfortable, but if you only need to do it every
10 years, then up with it you can surely put.

Will certainly give it a go, sure; just wondering what sort of volume of
air we're talking about shifting: am thinking it could be a fair bit?
Have since come across a stirrup pump affair on ebay with a 2m hose
which would probably cut the mustard if need be.

David

On 21 Jan,
Lobster wrote:


It's going to be fun trying to repressurise - the vessel is about 5 feet
off the ground in the airing cupboard, with nowhere nearby to site a
footpump.

Use it by hand (against the wall{protected}). It only takes a few pumps.

--
B Thumbs
Change lycos to yahoo to reply

Lobster wrote:

On 21/01/2011 11:58, Ronald Raygun wrote:

Just use the footpump.

Will certainly give it a go, sure; just wondering what sort of volume of
air we're talking about shifting: am thinking it could be a fair bit?

I wouldn't have thought so.

In article , davidlobsterpot601
@hotmail.com says...
I assumed I'd need to open a drain cock on the CH to reduce the pressure
to zero, thereby losing all that precious inhibitor - is that not the case?


No, that's on the heating side, not the hot water side. The heating
system pressurisation is a different kettle of fish and handled by the
boiler.
The pressure you're having trouble with is the hot water pressure - the
secondary, not the primary.

--
Skipweasel - never knowingly understood.

Lobster wrote:

On 21/01/2011 13:00, John Rumm wrote:
On 20/01/2011 22:12, Roger Mills wrote:
On 20/01/2011 21:23, Ron Lowe wrote:

P5 says the pre-charge pressure on the expansion vessel should be 4
bar.

THe 6 bar reference on P14 is the cracking pressure of the Expansion
Relief Valve.

Pump the thing up to 4 bar cold.


.. . . making sure that the 'wet' side isn't under pressure while you do
so.

which probably means shut off the mains inlet, and open a hot tap...

I assumed I'd need to open a drain cock on the CH to reduce the pressure
to zero, thereby losing all that precious inhibitor - is that not the
case?

No.

There are two distinct pressurised hot water circuits, each with their own
expansion vessels and pressure relief valves. One circuit is for the water
which circulates through boiler, radiators, and the heating coil inside the
HW cylinder, and its EV and PRV are usually located inside the boiler
housing. This is the water which has your inhibitor in it.

The other circuit is for the hot tap water, and this is the one where your
problem lies. Its EV is typically located within the HW cylinder. These
two circuits (heatING water and heatED water) are completely separate (you
don't want your inhibitor coming out of your HW taps) and are independently
pressurised. Your tap water is at the same water main pressure as your cold
tap water, and my understanding is that the only reason that your hot water
circuit needs an EV to absorb volume changes is that there is bound to be a
non-return valve somewhere (probably on the HW cylinder's cold water inlet)
to prevent back-flow from the hot water circuit back into the cold circuit
(the hot water circuit is at times tepid and is potentially a pleasant
breeding ground for bugs which could swim back into the public supply and
contaminate the whole neighbourhood). If it weren't for this NRV, it
would be a simple matter just to let the expanded heated water to "push back
against" the cold supply, and there would be no pressure problem. This is
similar to the state of affairs in a vented system, where expanding heated
water pushes back on the cold supply, which causes the level in your cold
water tank to rise a bit, and this is of course isolated from the public
supply by virtue of the cold water tank float valve outlet being clear of
the water surface.

In article , Lobster wrote:

Will certainly give it a go, sure; just wondering what sort of volume of
air we're talking about shifting: am thinking it could be a fair bit?

You see what volume the expansion vessel is? At most six times that much,
since you said it was supposed to be at six bar.

(Since the diaphragm means it will only be about half full of air when
you are done, and it isn't totally empty of air now, it'll be quite a
bit less than that in fact.)

On 21/01/2011 10:53, Lobster wrote:
On 20/01/2011 21:15, Ron Lowe wrote:
On 20/01/2011 20:10, Lobster wrote:

The system has been in for about 10 years with no problems up to now.

The expansion vessel has lost it's air volume.



Thanks for the responses. Just checked, and upon depressing the
Schraeder valve I'm rewarded with a barely perceptible little fart -
that's it - just enough to know that the valve was actually depressed.
I'll give repressurising a go first but presumably it'll need replacing.

If you got a small air volume, that's good. It probably indicates the
thing is not ruptured. It's just lost it's ait volume, and over 10
years, that's not bad. Just pump it up and see how it goes.

The 4 bar is a pre-charge pressu ie the pressure in the bladder
without eny external water pressure. So shut off the cold water inlet
to the cylinder, then open the lowest hot tap. Since there's no air
volume, it will stop running fairly quickly.

Pump it up unter these condtitions.

Shut the tap, and turn on the cold supply.

Isn't it a bit odd that my system works though? Have had CH and HW on
all week with no problems at all except apparently for the one
'overflow' issue.



No, the symptoms you describe are totally normal for this failure mode.

--
R

On 21/01/2011 10:53, Lobster wrote:
On 20/01/2011 21:15, Ron Lowe wrote:
On 20/01/2011 20:10, Lobster wrote:

The system has been in for about 10 years with no problems up to now.

The expansion vessel has lost it's air volume.



Thanks for the responses. Just checked, and upon depressing the
Schraeder valve I'm rewarded with a barely perceptible little fart -
that's it - just enough to know that the valve was actually depressed.
I'll give repressurising a go first but presumably it'll need replacing.

If you got a small air volume, that's good. It probably indicates the
thing is not ruptured. It's just lost it's ait volume, and over 10
years, that's not bad. Just pump it up and see how it goes.

The 4 bar is a pre-charge pressu ie the pressure in the bladder
without eny external water pressure. So shut off the cold water inlet
to the cylinder, then open the lowest hot tap. Since there's no air
volume, it will stop running fairly quickly.

Pump it up unter these condtitions.

Shut the tap, and turn on the cold supply.

Isn't it a bit odd that my system works though? Have had CH and HW on
all week with no problems at all except apparently for the one
'overflow' issue.



No, the symptoms you describe are totally normal for this failure mode.

--
R

Lobster wrote:
On 21/01/2011 13:00, John Rumm wrote:
On 20/01/2011 22:12, Roger Mills wrote:
On 20/01/2011 21:23, Ron Lowe wrote:

P5 says the pre-charge pressure on the expansion vessel should be 4
bar.

THe 6 bar reference on P14 is the cracking pressure of the Expansion
Relief Valve.

Pump the thing up to 4 bar cold.


.. . . making sure that the 'wet' side isn't under pressure while you do
so.

which probably means shut off the mains inlet, and open a hot tap...

I assumed I'd need to open a drain cock on the CH to reduce the pressure
to zero, thereby losing all that precious inhibitor - is that not the case?

David


no.

shut off mains supply, and open two hot taps, one upstairs and one down.

On 21/01/2011 17:17, Ronald Raygun wrote:
Lobster wrote:

On 21/01/2011 13:00, John Rumm wrote:
On 20/01/2011 22:12, Roger Mills wrote:
On 20/01/2011 21:23, Ron Lowe wrote:

P5 says the pre-charge pressure on the expansion vessel should be 4
bar.

THe 6 bar reference on P14 is the cracking pressure of the Expansion
Relief Valve.

Pump the thing up to 4 bar cold.


.. . . making sure that the 'wet' side isn't under pressure while you do
so.

which probably means shut off the mains inlet, and open a hot tap...

I assumed I'd need to open a drain cock on the CH to reduce the pressure
to zero, thereby losing all that precious inhibitor - is that not the
case?

No.

There are two distinct pressurised hot water circuits, each with their own
expansion vessels and pressure relief valves. One circuit is for the water
which circulates through boiler, radiators, and the heating coil inside the
HW cylinder, and its EV and PRV are usually located inside the boiler
housing. This is the water which has your inhibitor in it.

Update...

Well the expansion vessel was completely devoid of any pressure at all,
but at least there was no water leaking out so no probs with the
diaphragm. I then discovered a slow (air) leak on the Schraeder valve
so have replaced the valve core, and it seems to be holding OK so far.

Wasn't able to get more than 2.4 bar into the vessel using my footpump
against the wall at chest height - likely to be a problem? Bloody hard
work towards the end (yes the system was depressurised as direct!) -
should it be that difficult? Will it matter not getting to 4 bar?

I'd like to have replaced the whole valve not just the core. However: on
top of the vessel, the valve body is held in place by a retaining nut
(just as it would be on a bicycle tyre). It was easy to loosen the nut,
but it was clear to me if I removed it completely I'd just lose the
valve body for good down inside the expansion vessel! So didn't go
there... are these things supposed to be serviceable? Can the vessel be
dismantled to get at the innards, or will it be a bin job for the whole
vessel if my new core still doesn't work?

(It's a Varem 19-litre white - potable - vessel by the way, in case that
helps)

David

On 27/01/2011 15:45, Lobster wrote:


Update...

Well the expansion vessel was completely devoid of any pressure at all,
but at least there was no water leaking out so no probs with the
diaphragm. I then discovered a slow (air) leak on the Schraeder valve so
have replaced the valve core, and it seems to be holding OK so far.

Wasn't able to get more than 2.4 bar into the vessel using my footpump
against the wall at chest height - likely to be a problem? Bloody hard
work towards the end (yes the system was depressurised as direct!) -
should it be that difficult? Will it matter not getting to 4 bar?

Has your system got a pressure limiting valve on the cold feed? If so
what is it set to? Mine is set to 3.5 bar - and my expansion vessel is
also supposed to be pre-charged to 3.5 bar - so that water will only
enter it when it expands due to being heating.

If the vessel is pre-charged to less than the supply pressure, some of
its capacity will be taken up by the static cold pressure before it
starts to get hot. That may or may not matter - suck it and see! If you
have insufficient expansion capacity (remember, you started at zero!)
the PRV may continue to discharge when the water gets hot - but I doubt
whether that will happen.

I'd like to have replaced the whole valve not just the core. However: on
top of the vessel, the valve body is held in place by a retaining nut
(just as it would be on a bicycle tyre). It was easy to loosen the nut,
but it was clear to me if I removed it completely I'd just lose the
valve body for good down inside the expansion vessel! So didn't go
there... are these things supposed to be serviceable? Can the vessel be
dismantled to get at the innards, or will it be a bin job for the whole
vessel if my new core still doesn't work?


If the valve has the same thread as a car valve, you can simply fit a
screw-on metal cap containing a rubber washer - which will seal even if
the valve core doesn't.
--
Cheers,
Roger
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On 27/01/2011 15:45, Lobster wrote:

Wasn't able to get more than 2.4 bar into the vessel using my footpump
against the wall at chest height

Try a bike pump - most of them are Schraeder these days. A fiver for a
cheap one.

Andy

On 27/01/2011 23:29, John Rumm wrote:

Getting beyond 40psi on the cheap ones can be hard work though... A posh
stirrup pump style one would no doubt do it easily if you had a long hose.


Bet it's easier than a foot pump up against the wall... and anyway, I
run my bike tyres _way_ higher than 40 PSI.

Andy