I have a combi boiler feeding two small holiday cottages. Total of two large
radiators, two small radiators, two showers and kitchen sinks. There had
been a history of loss of pressure, so when the cottages were renovated and
the floors taken up (suspended floor) every joint was checked and there was
no evidence of leakage or staining so the floor was re-laid and tiled.
Everything pointed to the Worcester 20-25 boiler which had other problems
(it had already had it's expansion vessel, safety pressure valve and auto
air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if allowed to go
cold (power cut for example) the pressure would go to zero, no sign of any
pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we had a power
cut, and ARGH !!!!!! the pressure fell to zero. Re-pressurised and it was ok
for a few days - then the oil control solenoid failed (infant mortality?),
the boiler went cold, and again the pressure went to zero indicated on the
gauge. Last night again a repeat - system not working as no pressure this
morning - (it was fine when I checked it at 20:00 last evening).

So logically the leak is most unlikely to be the new boiler as the symptoms
are pretty well identical to the old one, which begs the question, how can a
leak suddenly develop, allow total loss of pressure, yet seal fine when the
system is topped up and show no evidence?

Andrew

On Wed, 26 Feb 2014 09:27:57 -0000
"Andrew Mawson" wrote:

I have a combi boiler feeding two small holiday cottages. Total of
two large radiators, two small radiators, two showers and kitchen
sinks. There had been a history of loss of pressure, so when the
cottages were renovated and the floors taken up (suspended floor)
every joint was checked and there was no evidence of leakage or
staining so the floor was re-laid and tiled. Everything pointed to
the Worcester 20-25 boiler which had other problems (it had already
had it's expansion vessel, safety pressure valve and auto air vent
changed).

Symptoms were that if the boiler stayed warm it was ok but if allowed
to go cold (power cut for example) the pressure would go to zero, no
sign of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we had a
power cut, and ARGH !!!!!! the pressure fell to zero. Re-pressurised
and it was ok for a few days - then the oil control solenoid failed
(infant mortality?), the boiler went cold, and again the pressure
went to zero indicated on the gauge. Last night again a repeat -
system not working as no pressure this morning - (it was fine when I
checked it at 20:00 last evening).

So logically the leak is most unlikely to be the new boiler as the
symptoms are pretty well identical to the old one, which begs the
question, how can a leak suddenly develop, allow total loss of
pressure, yet seal fine when the system is topped up and show no
evidence?

Andrew


I know nothing of pressurised boilers, but to me, it sounds as though
there is a powered normally-open solenoid valve somewhere, which fails
open, and lets the pressure out. Or a valve which needs a certain
minimum pressure to stay closed, and when the system goes cold, the
pressure drops below this.
Just thinking.

--
Davey.

"Andrew Mawson" wrote in message
...
Symptoms were that if the boiler stayed warm it was ok but if allowed to
go cold (power cut for example) the pressure would go to zero, no sign of
any pressure on the gauge what so ever.

Perhaps a system drain point which leads outside so there's no internal
evidence of leaks?

Other than that if the boiler itself has been changed and the rads don't
leak the only other things that could affect this would seem to be the
pressure relief valve or the non return valve on the filling loop.
--
Dave Baker

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total of two
large radiators, two small radiators, two showers and kitchen sinks.
There had been a history of loss of pressure, so when the cottages were
renovated and the floors taken up (suspended floor) every joint was
checked and there was no evidence of leakage or staining so the floor
was re-laid and tiled. Everything pointed to the Worcester 20-25 boiler
which had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if allowed to
go cold (power cut for example) the pressure would go to zero, no sign
of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we had a
power cut, and ARGH !!!!!! the pressure fell to zero. Re-pressurised and
it was ok for a few days - then the oil control solenoid failed (infant
mortality?), the boiler went cold, and again the pressure went to zero
indicated on the gauge. Last night again a repeat - system not working
as no pressure this morning - (it was fine when I checked it at 20:00
last evening).

So logically the leak is most unlikely to be the new boiler as the
symptoms are pretty well identical to the old one, which begs the
question, how can a leak suddenly develop, allow total loss of pressure,
yet seal fine when the system is topped up and show no evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external expansion
vessel (not replaced) with a failed diaphragm so that the system gets
overpressurised on warmup? In my experience if the "pressure relief
valve" has ever lifted it sometimes does not re-seal well (erosion of
seat from cavitation? deposits on seat?). So you could have had a failed
PRV on the old one, and now have a failed one on the new combi. The
"hot/cold" effect could be because sufficient pressure keeps it sealed
while it leaks at slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g. where
pipes pass through walls? Same hot/cold process (although this sounds
less likely than for the PRV which I think has a rubber seal).

"newshound" wrote in message
o.uk...

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total of two
large radiators, two small radiators, two showers and kitchen sinks.
There had been a history of loss of pressure, so when the cottages were
renovated and the floors taken up (suspended floor) every joint was
checked and there was no evidence of leakage or staining so the floor
was re-laid and tiled. Everything pointed to the Worcester 20-25 boiler
which had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if allowed to
go cold (power cut for example) the pressure would go to zero, no sign
of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we had a
power cut, and ARGH !!!!!! the pressure fell to zero. Re-pressurised and
it was ok for a few days - then the oil control solenoid failed (infant
mortality?), the boiler went cold, and again the pressure went to zero
indicated on the gauge. Last night again a repeat - system not working
as no pressure this morning - (it was fine when I checked it at 20:00
last evening).

So logically the leak is most unlikely to be the new boiler as the
symptoms are pretty well identical to the old one, which begs the
question, how can a leak suddenly develop, allow total loss of pressure,
yet seal fine when the system is topped up and show no evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external expansion vessel
(not replaced) with a failed diaphragm so that the system gets
overpressurised on warmup? In my experience if the "pressure relief valve"
has ever lifted it sometimes does not re-seal well (erosion of seat from
cavitation? deposits on seat?). So you could have had a failed PRV on the
old one, and now have a failed one on the new combi. The "hot/cold" effect
could be because sufficient pressure keeps it sealed while it leaks at
slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g. where
pipes pass through walls? Same hot/cold process (although this sounds less
likely than for the PRV which I think has a rubber seal).


Expansion vessel is incorporated in the boiler. as is the pressure relief
valve, all electrically operated valves (Honeywell zone valves) are in the
boiler room and visible. Leaks on the filling loop would increase boiler
pressure to mains water pressure not reduce it.

My only conclusion is that there MUST be an under floor leak, but we
searched every pipe and joint when the floor was replaced - it's a bit of a
b*****r

Andrew

Andrew Mawson wrote:
"newshound" wrote in message
o.uk...

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total of two
large radiators, two small radiators, two showers and kitchen sinks.
There had been a history of loss of pressure, so when the cottages were
renovated and the floors taken up (suspended floor) every joint was
checked and there was no evidence of leakage or staining so the floor
was re-laid and tiled. Everything pointed to the Worcester 20-25 boiler
which had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if allowed to
go cold (power cut for example) the pressure would go to zero, no sign
of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we had a
power cut, and ARGH !!!!!! the pressure fell to zero. Re-pressurised and
it was ok for a few days - then the oil control solenoid failed (infant
mortality?), the boiler went cold, and again the pressure went to zero
indicated on the gauge. Last night again a repeat - system not working
as no pressure this morning - (it was fine when I checked it at 20:00
last evening).

So logically the leak is most unlikely to be the new boiler as the
symptoms are pretty well identical to the old one, which begs the
question, how can a leak suddenly develop, allow total loss of pressure,
yet seal fine when the system is topped up and show no evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external expansion
vessel (not replaced) with a failed diaphragm so that the system gets
overpressurised on warmup? In my experience if the "pressure relief
valve" has ever lifted it sometimes does not re-seal well (erosion of
seat from cavitation? deposits on seat?). So you could have had a
failed PRV on the old one, and now have a failed one on the new combi.
The "hot/cold" effect could be because sufficient pressure keeps it
sealed while it leaks at slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g. where
pipes pass through walls? Same hot/cold process (although this sounds
less likely than for the PRV which I think has a rubber seal).


Expansion vessel is incorporated in the boiler. as is the pressure
relief valve, all electrically operated valves (Honeywell zone valves)
are in the boiler room and visible. Leaks on the filling loop would
increase boiler pressure to mains water pressure not reduce it.

My only conclusion is that there MUST be an under floor leak, but we
searched every pipe and joint when the floor was replaced - it's a bit
of a b*****r

Andrew


Is there any chance that there is air in the system? You state that the
system doesn't lose water when running hot, but loses pressure if it
cools down. With air in the system, wouldn't the pressure relief valve
come into operation when the system is hot, thereby losing water? I
don't know anything about these systems, just a thought.

"Capitol" wrote in message
o.uk...

Andrew Mawson wrote:
"newshound" wrote in message
o.uk...

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total of two
large radiators, two small radiators, two showers and kitchen sinks.
There had been a history of loss of pressure, so when the cottages were
renovated and the floors taken up (suspended floor) every joint was
checked and there was no evidence of leakage or staining so the floor
was re-laid and tiled. Everything pointed to the Worcester 20-25 boiler
which had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if allowed
to
go cold (power cut for example) the pressure would go to zero, no sign
of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we had a
power cut, and ARGH !!!!!! the pressure fell to zero. Re-pressurised
and
it was ok for a few days - then the oil control solenoid failed (infant
mortality?), the boiler went cold, and again the pressure went to zero
indicated on the gauge. Last night again a repeat - system not working
as no pressure this morning - (it was fine when I checked it at 20:00
last evening).

So logically the leak is most unlikely to be the new boiler as the
symptoms are pretty well identical to the old one, which begs the
question, how can a leak suddenly develop, allow total loss of
pressure,
yet seal fine when the system is topped up and show no evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external expansion
vessel (not replaced) with a failed diaphragm so that the system gets
overpressurised on warmup? In my experience if the "pressure relief
valve" has ever lifted it sometimes does not re-seal well (erosion of
seat from cavitation? deposits on seat?). So you could have had a
failed PRV on the old one, and now have a failed one on the new combi.
The "hot/cold" effect could be because sufficient pressure keeps it
sealed while it leaks at slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g. where
pipes pass through walls? Same hot/cold process (although this sounds
less likely than for the PRV which I think has a rubber seal).


Expansion vessel is incorporated in the boiler. as is the pressure
relief valve, all electrically operated valves (Honeywell zone valves)
are in the boiler room and visible. Leaks on the filling loop would
increase boiler pressure to mains water pressure not reduce it.

My only conclusion is that there MUST be an under floor leak, but we
searched every pipe and joint when the floor was replaced - it's a bit
of a b*****r

Andrew


Is there any chance that there is air in the system? You state that the
system doesn't lose water when running hot, but loses pressure if it cools
down. With air in the system, wouldn't the pressure relief valve come into
operation when the system is hot, thereby losing water? I don't know
anything about these systems, just a thought.


"....just a thought. " and indeed a very good one. The whole system is so
small, confined to one floor, and we think we've got all the air out. I
agree it might explain things but I don't sadly think it is the reason.

Any midget DIYers want to have a crawl under the floor

Andrew

On Wed, 26 Feb 2014 15:52:20 -0000
"Andrew Mawson" wrote:

"Capitol" wrote in message
o.uk...

Andrew Mawson wrote:
"newshound" wrote in message
o.uk...

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total
of two large radiators, two small radiators, two showers and
kitchen sinks. There had been a history of loss of pressure, so
when the cottages were renovated and the floors taken up
(suspended floor) every joint was checked and there was no
evidence of leakage or staining so the floor was re-laid and
tiled. Everything pointed to the Worcester 20-25 boiler which
had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if
allowed to
go cold (power cut for example) the pressure would go to zero,
no sign of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we
had a power cut, and ARGH !!!!!! the pressure fell to zero.
Re-pressurised and
it was ok for a few days - then the oil control solenoid failed
(infant mortality?), the boiler went cold, and again the
pressure went to zero indicated on the gauge. Last night again a
repeat - system not working as no pressure this morning - (it
was fine when I checked it at 20:00 last evening).

So logically the leak is most unlikely to be the new boiler as
the symptoms are pretty well identical to the old one, which
begs the question, how can a leak suddenly develop, allow total
loss of pressure,
yet seal fine when the system is topped up and show no evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external
expansion vessel (not replaced) with a failed diaphragm so that
the system gets overpressurised on warmup? In my experience if
the "pressure relief valve" has ever lifted it sometimes does not
re-seal well (erosion of seat from cavitation? deposits on
seat?). So you could have had a failed PRV on the old one, and
now have a failed one on the new combi. The "hot/cold" effect
could be because sufficient pressure keeps it sealed while it
leaks at slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g.
where pipes pass through walls? Same hot/cold process (although
this sounds less likely than for the PRV which I think has a
rubber seal).


Expansion vessel is incorporated in the boiler. as is the pressure
relief valve, all electrically operated valves (Honeywell zone
valves) are in the boiler room and visible. Leaks on the filling
loop would increase boiler pressure to mains water pressure not
reduce it.

My only conclusion is that there MUST be an under floor leak, but
we searched every pipe and joint when the floor was replaced -
it's a bit of a b*****r

Andrew


Is there any chance that there is air in the system? You state that
the system doesn't lose water when running hot, but loses pressure
if it cools down. With air in the system, wouldn't the pressure
relief valve come into operation when the system is hot, thereby
losing water? I don't know anything about these systems, just a
thought.


"....just a thought. " and indeed a very good one. The whole system
is so small, confined to one floor, and we think we've got all
the air out. I agree it might explain things but I don't sadly think
it is the reason.

Any midget DIYers want to have a crawl under the floor

Andrew


You need a ferret-mounted camera........

--
Davey.

Davey wrote:
On Wed, 26 Feb 2014 15:52:20 -0000
"Andrew wrote:

"Capitol" wrote in message
o.uk...

Andrew Mawson wrote:
"newshound" wrote in message
o.uk...

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total
of two large radiators, two small radiators, two showers and
kitchen sinks. There had been a history of loss of pressure, so
when the cottages were renovated and the floors taken up
(suspended floor) every joint was checked and there was no
evidence of leakage or staining so the floor was re-laid and
tiled. Everything pointed to the Worcester 20-25 boiler which
had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if
allowed to
go cold (power cut for example) the pressure would go to zero,
no sign of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we
had a power cut, and ARGH !!!!!! the pressure fell to zero.
Re-pressurised and
it was ok for a few days - then the oil control solenoid failed
(infant mortality?), the boiler went cold, and again the
pressure went to zero indicated on the gauge. Last night again a
repeat - system not working as no pressure this morning - (it
was fine when I checked it at 20:00 last evening).

So logically the leak is most unlikely to be the new boiler as
the symptoms are pretty well identical to the old one, which
begs the question, how can a leak suddenly develop, allow total
loss of pressure,
yet seal fine when the system is topped up and show no evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external
expansion vessel (not replaced) with a failed diaphragm so that
the system gets overpressurised on warmup? In my experience if
the "pressure relief valve" has ever lifted it sometimes does not
re-seal well (erosion of seat from cavitation? deposits on
seat?). So you could have had a failed PRV on the old one, and
now have a failed one on the new combi. The "hot/cold" effect
could be because sufficient pressure keeps it sealed while it
leaks at slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g.
where pipes pass through walls? Same hot/cold process (although
this sounds less likely than for the PRV which I think has a
rubber seal).


Expansion vessel is incorporated in the boiler. as is the pressure
relief valve, all electrically operated valves (Honeywell zone
valves) are in the boiler room and visible. Leaks on the filling
loop would increase boiler pressure to mains water pressure not
reduce it.

My only conclusion is that there MUST be an under floor leak, but
we searched every pipe and joint when the floor was replaced -
it's a bit of a b*****r

Andrew


Is there any chance that there is air in the system? You state that
the system doesn't lose water when running hot, but loses pressure
if it cools down. With air in the system, wouldn't the pressure
relief valve come into operation when the system is hot, thereby
losing water? I don't know anything about these systems, just a
thought.


"....just a thought. " and indeed a very good one. The whole system
is so small, confined to one floor, and wethink we've got all
the air out. I agree it might explain things but I don't sadly think
it is the reason.

Any midget DIYers want to have a crawl under the floor

Andrew


You need a ferret-mounted camera........


Wireless I assume?

On Wed, 26 Feb 2014 16:22:31 +0000
Capitol wrote:

Davey wrote:
On Wed, 26 Feb 2014 15:52:20 -0000
"Andrew wrote:

"Capitol" wrote in message
o.uk...

Andrew Mawson wrote:
"newshound" wrote in message
o.uk...

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total
of two large radiators, two small radiators, two showers and
kitchen sinks. There had been a history of loss of pressure, so
when the cottages were renovated and the floors taken up
(suspended floor) every joint was checked and there was no
evidence of leakage or staining so the floor was re-laid and
tiled. Everything pointed to the Worcester 20-25 boiler which
had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if
allowed to
go cold (power cut for example) the pressure would go to zero,
no sign of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we
had a power cut, and ARGH !!!!!! the pressure fell to zero.
Re-pressurised and
it was ok for a few days - then the oil control solenoid failed
(infant mortality?), the boiler went cold, and again the
pressure went to zero indicated on the gauge. Last night again
a repeat - system not working as no pressure this morning - (it
was fine when I checked it at 20:00 last evening).

So logically the leak is most unlikely to be the new boiler as
the symptoms are pretty well identical to the old one, which
begs the question, how can a leak suddenly develop, allow total
loss of pressure,
yet seal fine when the system is topped up and show no
evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external
expansion vessel (not replaced) with a failed diaphragm so that
the system gets overpressurised on warmup? In my experience if
the "pressure relief valve" has ever lifted it sometimes does
not re-seal well (erosion of seat from cavitation? deposits on
seat?). So you could have had a failed PRV on the old one, and
now have a failed one on the new combi. The "hot/cold" effect
could be because sufficient pressure keeps it sealed while it
leaks at slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g.
where pipes pass through walls? Same hot/cold process (although
this sounds less likely than for the PRV which I think has a
rubber seal).


Expansion vessel is incorporated in the boiler. as is the
pressure relief valve, all electrically operated valves
(Honeywell zone valves) are in the boiler room and visible.
Leaks on the filling loop would increase boiler pressure to
mains water pressure not reduce it.

My only conclusion is that there MUST be an under floor leak, but
we searched every pipe and joint when the floor was replaced -
it's a bit of a b*****r

Andrew


Is there any chance that there is air in the system? You state
that the system doesn't lose water when running hot, but loses
pressure if it cools down. With air in the system, wouldn't the
pressure relief valve come into operation when the system is hot,
thereby losing water? I don't know anything about these systems,
just a thought.


"....just a thought. " and indeed a very good one. The whole system
is so small, confined to one floor, and wethink we've got all
the air out. I agree it might explain things but I don't sadly
think it is the reason.

Any midget DIYers want to have a crawl under the floor

Andrew


You need a ferret-mounted camera........


Wireless I assume?

There was a guy on TV recently who swallowed a pill with a camera
inside, so that he could see, live, pictures of the inside of his
stomach and intestines. He had deliberately swallowed tapeworm cysts,
and the resulting tapeworms were clearly visible.

--
Davey.

On 26/02/2014 15:52, Andrew Mawson wrote:
"Capitol" wrote in message
o.uk...

Andrew Mawson wrote:
"newshound" wrote in message
o.uk...

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total of two
large radiators, two small radiators, two showers and kitchen sinks.
There had been a history of loss of pressure, so when the cottages
were
renovated and the floors taken up (suspended floor) every joint was
checked and there was no evidence of leakage or staining so the floor
was re-laid and tiled. Everything pointed to the Worcester 20-25
boiler
which had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if
allowed to
go cold (power cut for example) the pressure would go to zero, no sign
of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we had a
power cut, and ARGH !!!!!! the pressure fell to zero.
Re-pressurised and
it was ok for a few days - then the oil control solenoid failed
(infant
mortality?), the boiler went cold, and again the pressure went to zero
indicated on the gauge. Last night again a repeat - system not working
as no pressure this morning - (it was fine when I checked it at 20:00
last evening).

So logically the leak is most unlikely to be the new boiler as the
symptoms are pretty well identical to the old one, which begs the
question, how can a leak suddenly develop, allow total loss of
pressure,
yet seal fine when the system is topped up and show no evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external expansion
vessel (not replaced) with a failed diaphragm so that the system gets
overpressurised on warmup? In my experience if the "pressure relief
valve" has ever lifted it sometimes does not re-seal well (erosion of
seat from cavitation? deposits on seat?). So you could have had a
failed PRV on the old one, and now have a failed one on the new combi.
The "hot/cold" effect could be because sufficient pressure keeps it
sealed while it leaks at slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g. where
pipes pass through walls? Same hot/cold process (although this sounds
less likely than for the PRV which I think has a rubber seal).


Expansion vessel is incorporated in the boiler. as is the pressure
relief valve, all electrically operated valves (Honeywell zone valves)
are in the boiler room and visible. Leaks on the filling loop would
increase boiler pressure to mains water pressure not reduce it.

My only conclusion is that there MUST be an under floor leak, but we
searched every pipe and joint when the floor was replaced - it's a bit
of a b*****r

Andrew


Is there any chance that there is air in the system? You state that
the system doesn't lose water when running hot, but loses pressure if
it cools down. With air in the system, wouldn't the pressure relief
valve come into operation when the system is hot, thereby losing
water? I don't know anything about these systems, just a thought.


"....just a thought. " and indeed a very good one. The whole system is
so small, confined to one floor, and we think we've got all the air
out. I agree it might explain things but I don't sadly think it is the
reason.

Any midget DIYers want to have a crawl under the floor

Snake cams are pretty affordable.

Are these copper or plastic pipes?

When filling from 0 to say 1 bar, how long does it take to fill? It
sounds a modest leak.

Have you checked the pressure relief valve vent pipe, to see if any
water comes out when running?

Air is very compressible, so wouldn't be much different to the air in
the expansion vessel.

"Fredxxx" wrote in message ...

On 26/02/2014 15:52, Andrew Mawson wrote:
"Capitol" wrote in message
o.uk...

Andrew Mawson wrote:
"newshound" wrote in message
o.uk...

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total of
two
large radiators, two small radiators, two showers and kitchen sinks.
There had been a history of loss of pressure, so when the cottages
were
renovated and the floors taken up (suspended floor) every joint was
checked and there was no evidence of leakage or staining so the floor
was re-laid and tiled. Everything pointed to the Worcester 20-25
boiler
which had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if
allowed to
go cold (power cut for example) the pressure would go to zero, no
sign
of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we had a
power cut, and ARGH !!!!!! the pressure fell to zero.
Re-pressurised and
it was ok for a few days - then the oil control solenoid failed
(infant
mortality?), the boiler went cold, and again the pressure went to
zero
indicated on the gauge. Last night again a repeat - system not
working
as no pressure this morning - (it was fine when I checked it at 20:00
last evening).

So logically the leak is most unlikely to be the new boiler as the
symptoms are pretty well identical to the old one, which begs the
question, how can a leak suddenly develop, allow total loss of
pressure,
yet seal fine when the system is topped up and show no evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external expansion
vessel (not replaced) with a failed diaphragm so that the system gets
overpressurised on warmup? In my experience if the "pressure relief
valve" has ever lifted it sometimes does not re-seal well (erosion of
seat from cavitation? deposits on seat?). So you could have had a
failed PRV on the old one, and now have a failed one on the new combi.
The "hot/cold" effect could be because sufficient pressure keeps it
sealed while it leaks at slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g. where
pipes pass through walls? Same hot/cold process (although this sounds
less likely than for the PRV which I think has a rubber seal).


Expansion vessel is incorporated in the boiler. as is the pressure
relief valve, all electrically operated valves (Honeywell zone valves)
are in the boiler room and visible. Leaks on the filling loop would
increase boiler pressure to mains water pressure not reduce it.

My only conclusion is that there MUST be an under floor leak, but we
searched every pipe and joint when the floor was replaced - it's a bit
of a b*****r

Andrew


Is there any chance that there is air in the system? You state that
the system doesn't lose water when running hot, but loses pressure if
it cools down. With air in the system, wouldn't the pressure relief
valve come into operation when the system is hot, thereby losing
water? I don't know anything about these systems, just a thought.


"....just a thought. " and indeed a very good one. The whole system is
so small, confined to one floor, and we think we've got all the air
out. I agree it might explain things but I don't sadly think it is the
reason.

Any midget DIYers want to have a crawl under the floor

Snake cams are pretty affordable.

Are these copper or plastic pipes?

When filling from 0 to say 1 bar, how long does it take to fill? It sounds
a modest leak.

Have you checked the pressure relief valve vent pipe, to see if any water
comes out when running?

Air is very compressible, so wouldn't be much different to the air in the
expansion vessel.


Unfortunately it's plastic pipe. Re-pressurising takes perhaps 10 seconds,
no sign of leaks from the pressure relief vent pipe

Andrew

Andrew Mawson wrote:

Unfortunately it's plastic pipe. Re-pressurising takes perhaps 10
seconds, no sign of leaks from the pressure relief vent pipe

Andrew
Are there push fit joints under the floor?

"Capitol" wrote in message
...

Andrew Mawson wrote:

Unfortunately it's plastic pipe. Re-pressurising takes perhaps 10
seconds, no sign of leaks from the pressure relief vent pipe

Andrew
Are there push fit joints under the floor?

Sadly yes
Andrew

Andrew Mawson wrote:
"Capitol" wrote in message
...

Andrew Mawson wrote:

Unfortunately it's plastic pipe. Re-pressurising takes perhaps 10
seconds, no sign of leaks from the pressure relief vent pipe

Andrew
Are there push fit joints under the floor?

Sadly yes
Andrew

Oh dear! Looks like a camera job is called for. What's the floor! Does
it come up in sections? Or, can you procrastinate and say, we'll pretend
it isn't happening? Just make sure the water is kept hot!

"Capitol" wrote in message
o.uk...

Andrew Mawson wrote:
"Capitol" wrote in message
...

Andrew Mawson wrote:

Unfortunately it's plastic pipe. Re-pressurising takes perhaps 10
seconds, no sign of leaks from the pressure relief vent pipe

Andrew
Are there push fit joints under the floor?

Sadly yes
Andrew

Oh dear! Looks like a camera job is called for. What's the floor! Does it
come up in sections? Or, can you procrastinate and say, we'll pretend it
isn't happening? Just make sure the water is kept hot!

Floor is 18 mm plywood, tiled all over

Plumber has suggested an automatic top up system that fills from a reservoir
of Fernox treated water. OK I suppose if I can monitor water usage to see if
it escalates. The very odd thing is it can be fine for weeks, or at lease
has been previously.

Andrew

On Thu, 27 Feb 2014 12:24:31 -0000
"Andrew Mawson" wrote:

"Capitol" wrote in message
o.uk...

Andrew Mawson wrote:
"Capitol" wrote in message
...

Andrew Mawson wrote:

Unfortunately it's plastic pipe. Re-pressurising takes perhaps 10
seconds, no sign of leaks from the pressure relief vent pipe

Andrew
Are there push fit joints under the floor?

Sadly yes
Andrew

Oh dear! Looks like a camera job is called for. What's the floor!
Does it come up in sections? Or, can you procrastinate and say,
we'll pretend it isn't happening? Just make sure the water is kept
hot!

Floor is 18 mm plywood, tiled all over

Plumber has suggested an automatic top up system that fills from a
reservoir of Fernox treated water. OK I suppose if I can monitor
water usage to see if it escalates. The very odd thing is it can be
fine for weeks, or at lease has been previously.

Andrew


Ah! So you need to use a leak-plugging additive! My sympathies for this
one.

--
Davey.

Andrew Mawson wrote:
"Fredxxx" wrote in message ...

On 26/02/2014 15:52, Andrew Mawson wrote:
"Capitol" wrote in message
o.uk...

Andrew Mawson wrote:
"newshound" wrote in message
o.uk...

On 26/02/2014 09:27, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total
of two
large radiators, two small radiators, two showers and kitchen sinks.
There had been a history of loss of pressure, so when the cottages
were
renovated and the floors taken up (suspended floor) every joint was
checked and there was no evidence of leakage or staining so the
floor
was re-laid and tiled. Everything pointed to the Worcester 20-25
boiler
which had other problems (it had already had it's expansion vessel,
safety pressure valve and auto air vent changed).

Symptoms were that if the boiler stayed warm it was ok but if
allowed to
go cold (power cut for example) the pressure would go to zero, no
sign
of any pressure on the gauge what so ever.

So we had the boiler replaced (Grant Vortex 21 combi). Then we had a
power cut, and ARGH !!!!!! the pressure fell to zero.
Re-pressurised and
it was ok for a few days - then the oil control solenoid failed
(infant
mortality?), the boiler went cold, and again the pressure went to
zero
indicated on the gauge. Last night again a repeat - system not
working
as no pressure this morning - (it was fine when I checked it at
20:00
last evening).

So logically the leak is most unlikely to be the new boiler as the
symptoms are pretty well identical to the old one, which begs the
question, how can a leak suddenly develop, allow total loss of
pressure,
yet seal fine when the system is topped up and show no evidence?

Andrew

I agree it sounds pretty odd. Is there perhaps an external expansion
vessel (not replaced) with a failed diaphragm so that the system gets
overpressurised on warmup? In my experience if the "pressure relief
valve" has ever lifted it sometimes does not re-seal well (erosion of
seat from cavitation? deposits on seat?). So you could have had a
failed PRV on the old one, and now have a failed one on the new
combi.
The "hot/cold" effect could be because sufficient pressure keeps it
sealed while it leaks at slightly lower pressure.

Or of course could there be a leak somewhere uninspectable, e.g.
where
pipes pass through walls? Same hot/cold process (although this sounds
less likely than for the PRV which I think has a rubber seal).


Expansion vessel is incorporated in the boiler. as is the pressure
relief valve, all electrically operated valves (Honeywell zone valves)
are in the boiler room and visible. Leaks on the filling loop would
increase boiler pressure to mains water pressure not reduce it.

My only conclusion is that there MUST be an under floor leak, but we
searched every pipe and joint when the floor was replaced - it's a bit
of a b*****r

Andrew


Is there any chance that there is air in the system? You state that
the system doesn't lose water when running hot, but loses pressure if
it cools down. With air in the system, wouldn't the pressure relief
valve come into operation when the system is hot, thereby losing
water? I don't know anything about these systems, just a thought.


"....just a thought. " and indeed a very good one. The whole system is
so small, confined to one floor, and we think we've got all the air
out. I agree it might explain things but I don't sadly think it is the
reason.

Any midget DIYers want to have a crawl under the floor

Snake cams are pretty affordable.

Are these copper or plastic pipes?

When filling from 0 to say 1 bar, how long does it take to fill? It
sounds a modest leak.

Have you checked the pressure relief valve vent pipe, to see if any
water comes out when running?

Air is very compressible, so wouldn't be much different to the air in
the expansion vessel.


Unfortunately it's plastic pipe. Re-pressurising takes perhaps 10
seconds, no sign of leaks from the pressure relief vent pipe

Andrew
If you can re-pressurise in seconds then I think it is unlikely that you
have a lot of air in the system.
You said somewhere that there is no sign of water coming from the PRV
drain - which would be a common culprit

I can only suggest adding a dye to the water and look for under floor weeps.

The other 'fix' which I could not possibly condone is the fit a pressure
regulator, set to the preferred cold pressure setting, upstream from the
filling loop and its NRV and leave the fill valve open a crack.

Incidentally I find having such a pressure regulator on my fill loop
very useful indeed - even though I DONT leave the fill valve open.
It makes bleeding and refilling a breeze with no concerns of over
pressurising.

Bob

On Wednesday, February 26, 2014 2:29:58 PM UTC, Andrew Mawson wrote:

My only conclusion is that there MUST be an under floor leak, but we

searched every pipe and joint when the floor was replaced - it's a bit of a

b*****r

Did you pressure test it?

I used to witness pressure tests, before the insulation went on, and contractors would have countless cunning stunts to try to get a leak through;
pump up the pressure when (they think) you're not looking, valve off the leaking bit that they'd already insulated, etc., etc.

The plastic pipe stretches and a different test procedure is used. The 10 bar test is part of the makers' warranty and must be done to set the grip rings on installation.

It sounds like it might be a plastic pipe pulling on a fitting when it's cold & shortest. They expand a lot when hot.

On Thursday, February 27, 2014 1:19:38 PM UTC, Onetap wrote:

The plastic pipe stretches and a different test procedure is used. The 10 bar test is part of the makers' warranty and must be done to set the grip rings on installation.

10 bar HYDRAULIC test.

On Wednesday, February 26, 2014 9:27:57 AM UTC, Andrew Mawson wrote:

So logically the leak is most unlikely to be the new boiler as the symptoms

are pretty well identical to the old one......

Yes, but not impossible.

I've seen a new boiler that leaked. The makers replaced it when asked to advise, but it seemed there was a known defect that they wouldn't volunteer information about.

On Wednesday, February 26, 2014 9:27:57 AM UTC, Andrew Mawson wrote:
I have a combi boiler feeding two small holiday cottages. Total of two large


Expansion vessel replaced with new boiler?

Expansion vessel big enough?

An undersized or over pressurized one would do as described, but would chuck water out the pressure relief valve when the system is first heated after refilling.

"Capitol" wrote in message
...

Andrew Mawson wrote:

Unfortunately it's plastic pipe. Re-pressurising takes perhaps 10
seconds, no sign of leaks from the pressure relief vent pipe

Andrew
Are there push fit joints under the floor?

Sadly yes
Andrew

I believe you said at one point that this is a very small system. If I'm
correct then I'm beginning to think your problem could be with a wrongly set
up pressure vessel. The sealed system installed in my last house and my sons
house had a bladder in a cylinder that had to be pressurised to the correct
PSI. I'm thinking that a very small system has little volume to pressurise
so could quickly lose it with temperature changes such as the boiler
shutting down.

Just think of a garden sprayer. If its too full there is too little air to
pressurise, and it doesn't spray for long. Half fill it and pump to the
same PSI and it sprays for much longer. This is because you can pressurise
air to a far greater degree than liquid.

Its the same with pressurised borehole/well pumped water supplies. The pump
forces water into a pressure vessel but its not the water in there that is
compressed it air inside a bladder within the vessel . That bladder of air
then expands forcing the stored water out through the system to the taps
etc. That bladder has to be kept at the correct PSI for the system to work.

Perhaps you need a better/more suitable pressure vessel than the one built
into the boiler, or it adjusting to a more suitable PSI to allow a larger
volume of pressurised air.

Mike

"Muddymike" wrote in message
om...

"Capitol" wrote in message
...

Andrew Mawson wrote:

Unfortunately it's plastic pipe. Re-pressurising takes perhaps 10
seconds, no sign of leaks from the pressure relief vent pipe

Andrew
Are there push fit joints under the floor?

Sadly yes
Andrew

I believe you said at one point that this is a very small system. If I'm
correct then I'm beginning to think your problem could be with a wrongly
set up pressure vessel. The sealed system installed in my last house and my
sons house had a bladder in a cylinder that had to be pressurised to the
correct PSI. I'm thinking that a very small system has little volume to
pressurise so could quickly lose it with temperature changes such as the
boiler shutting down.

Just think of a garden sprayer. If its too full there is too little air to
pressurise, and it doesn't spray for long. Half fill it and pump to the
same PSI and it sprays for much longer. This is because you can pressurise
air to a far greater degree than liquid.

Its the same with pressurised borehole/well pumped water supplies. The pump
forces water into a pressure vessel but its not the water in there that is
compressed it air inside a bladder within the vessel . That bladder of air
then expands forcing the stored water out through the system to the taps
etc. That bladder has to be kept at the correct PSI for the system to work.

Perhaps you need a better/more suitable pressure vessel than the one built
into the boiler, or it adjusting to a more suitable PSI to allow a larger
volume of pressurised air.

Mike

I don't think that it's an expansion vessel issue. The old boiler had it's
expansion vessel replaced as a part of the diagnosis, and I personally
checked it's bladder pressure as 0.5 bar as specified.

I don't think water is escaping from the over pressure vent, however I
picked up (maybe from a respondant to this thread) the idea of putting a
balloon on the outlet as a positive test, and I'll certainly do that as in
this rainy weather it's hard otherwise to be certain.

Andrew

On Thursday, February 27, 2014 3:00:30 PM UTC, Andrew Mawson wrote:

I don't think that it's an expansion vessel issue. The old boiler had it's

expansion vessel replaced as a part of the diagnosis, and I personally

checked it's bladder pressure as 0.5 bar as specified.

Where was 0.5 bar specified? It seems low, 1 bar is more usual I think.
What water pressure do you fill it to when you refill it?

"Onetap" wrote in message
...

On Thursday, February 27, 2014 3:00:30 PM UTC, Andrew Mawson wrote:

I don't think that it's an expansion vessel issue. The old boiler had
it's

expansion vessel replaced as a part of the diagnosis, and I personally

checked it's bladder pressure as 0.5 bar as specified.

Where was 0.5 bar specified? It seems low, 1 bar is more usual I think.
What water pressure do you fill it to when you refill it?

0.5 bar is spec'd in the Worcester 20-25 installation manual for a system
all on one floor with a smallish system volume, with system cold and fully
depressurised - I also was surprised. Filling pressure is 1.2 bar. Don't
know the spec on my replacement which is a Grant Vortex 21 combi.

Andrew

On Thursday, February 27, 2014 9:36:26 PM UTC, Andrew Mawson wrote:

0.5 bar is spec'd in the Worcester 20-25 installation manual for a system

all on one floor with a smallish system volume, with system cold and fully

depressurised - I also was surprised. Filling pressure is 1.2 bar. Don't

know the spec on my replacement which is a Grant Vortex 21 combi.

That may be your problem.

Half (?) the expansion vessel volume is used up when you fill it cold. The remaining volume is then inadequate to accommodate the expansion and the excess water volume goes out the PRV when the water gets hot.

I'd have thought 1 bar air charge (no water pressure) and 1 bar fill pressure.

"Onetap" wrote in message
...

On Thursday, February 27, 2014 9:36:26 PM UTC, Andrew Mawson wrote:

0.5 bar is spec'd in the Worcester 20-25 installation manual for a system

all on one floor with a smallish system volume, with system cold and
fully

depressurised - I also was surprised. Filling pressure is 1.2 bar. Don't

know the spec on my replacement which is a Grant Vortex 21 combi.

That may be your problem.

Half (?) the expansion vessel volume is used up when you fill it cold. The
remaining volume is then inadequate to accommodate the expansion and the
excess water volume goes out the PRV when the water gets hot.

I'd have thought 1 bar air charge (no water pressure) and 1 bar fill
pressure.

Before the boiler was changed, and as part of the leak investigation, I
charged the (recently replaced as a diagnostic aid) expansion cylinder to 1
bar. It was after that hadn't changed the symptom I googled for Worcesters
spec and found it was supposed to be 0.5, as it had been

Andrew

On Friday, February 28, 2014 8:12:21 AM UTC, Andrew Mawson wrote:

Before the boiler was changed, and as part of the leak investigation, I

charged the (recently replaced as a diagnostic aid) expansion cylinder to 1

bar. It was after that hadn't changed the symptom I googled for Worcesters

spec and found it was supposed to be 0.5, as it had been

I still think that is probably where your problem lies.

The simple solution is to check the expansion vessel pre-charge pressure (drain boiler first), recharge the heating system and watch the pressure gauge as it first heats up, with a container/balloon catching water from the PRV discharge.

If it is an expansion volume problem, the PG will rise to the PRV set pressure (usually 3 bar, but gauges are often inaccurate) and stay there whilst the boiler is hot. On cooling it will drop to 0. You should get a discharge from the PRV; the discharge pipe should have a continuous fall to the outlet.