Hi,

I have an open-vented, S-plan system with two 2-port zone
valves, 28mm to hot water cylinder and 22 mm, dropping to 15mm,
to radiators. There is an automatic bypass valve fitted
in a loop-back circuit.

Last winter I started to get a banging noise from the central
heating system. The noise was a load bang in the pipework
that occured intermittently shortly after the heating cut out.

I think this is described as water-hammer?

As it happened, I was in need of a new boiler anyway, and arranged
for British Gas to come and install a new boiler, pump and zone
valves. (Pause to wait for traditional BG insults). The idea here
was to change everything that could cause the water hammer.

The radiators in the system (13 mixed sizes) were newly fitted
about 3 years ago.

So, BG went ahead gave the system a chemical clean, and installed
a 300+ HE boiler, new pump and new bypass valve but, due to some
admin cock-up, new zone valves were not fitted, so I'm left with
the old ones.

When I complained about this, BG told me that there is nothing wrong
with my existing zone valves and that the replacement bypass valve
should fix the loud-bang-as-zone-valve-closes problem.

Sadly, this turned out not to be the case, and I am still
getting the load bangs with the (mostly) all-new system.

Would any CH guru out there care to suggest what is
causing the water hammer and what I need to get BG
to do to fix it? Is it possible/likely that the zone
valves are to blame or am I fixating on them unnecessarily?

I'm currently waiting a call-back from BG and would like to
prepare myself with what options there are to diagnose
and fix this problem.

Many thanks.

On 29 Oct, 10:38, "Mike Smith"
wrote:
Hi,

I have an open-vented, S-plan system with two 2-port zone
valves, 28mm to hot water cylinder and 22 mm, dropping to 15mm,
to radiators. There is an automatic bypass valve fitted
in a loop-back circuit.

Last winter I started to get a banging noise from the central
heating system. The noise was a load bang in the pipework
that occured intermittently shortly after the heating cut out.

I think this is described as water-hammer?

As it happened, I was in need of a new boiler anyway, and arranged
for British Gas to come and install a new boiler, pump and zone
valves. (Pause to wait for traditional BG insults). The idea here
was to change everything that could cause the water hammer.

The radiators in the system (13 mixed sizes) were newly fitted
about 3 years ago.

So, BG went ahead gave the system a chemical clean, and installed
a 300+ HE boiler, new pump and new bypass valve but, due to some
admin cock-up, new zone valves were not fitted, so I'm left with
the old ones.

When I complained about this, BG told me that there is nothing wrong
with my existing zone valves and that the replacement bypass valve
should fix the loud-bang-as-zone-valve-closes problem.

Sadly, this turned out not to be the case, and I am still
getting the load bangs with the (mostly) all-new system.

Would any CH guru out there care to suggest what is
causing the water hammer and what I need to get BG
to do to fix it? Is it possible/likely that the zone
valves are to blame or am I fixating on them unnecessarily?

I'm currently waiting a call-back from BG and would like to
prepare myself with what options there are to diagnose
and fix this problem.

Many thanks.

You may want to check the setting of the auto bypass valve. I had a
boiler replaced last year, and it looked like the installer forgot to
set up the bypass valve. This caused some banging when the stats
switched. I adjusted the bypass and it cleared the problem.

John

Mike Smith wrote:
Hi,

I have an open-vented, S-plan system with two 2-port zone
valves, 28mm to hot water cylinder and 22 mm, dropping to 15mm,
to radiators. There is an automatic bypass valve fitted
in a loop-back circuit.

Last winter I started to get a banging noise from the central
heating system. The noise was a load bang in the pipework
that occured intermittently shortly after the heating cut out.

I think this is described as water-hammer?

As it happened, I was in need of a new boiler anyway, and arranged
for British Gas to come and install a new boiler, pump and zone
valves. (Pause to wait for traditional BG insults). The idea here
was to change everything that could cause the water hammer.

The radiators in the system (13 mixed sizes) were newly fitted
about 3 years ago.

So, BG went ahead gave the system a chemical clean, and installed
a 300+ HE boiler, new pump and new bypass valve but, due to some
admin cock-up, new zone valves were not fitted, so I'm left with
the old ones.

When I complained about this, BG told me that there is nothing wrong
with my existing zone valves and that the replacement bypass valve
should fix the loud-bang-as-zone-valve-closes problem.

Sadly, this turned out not to be the case, and I am still
getting the load bangs with the (mostly) all-new system.

Would any CH guru out there care to suggest what is
causing the water hammer and what I need to get BG
to do to fix it? Is it possible/likely that the zone
valves are to blame or am I fixating on them unnecessarily?

I'm currently waiting a call-back from BG and would like to
prepare myself with what options there are to diagnose
and fix this problem.

I wonder if you might have an old directional zone valve that has been
fittted the wrong way around? It may be that with a bit of slack developing
in the actuating mechanism, the ball in the valve is bouncing on its seat?

Work out which way the water is flowing though your valves (feel for which
side heats up first when the system is turned on) and make sure that this
agrees with the direction indicated by the arrow (if present) on your
motorised valve.

Of course, if it was agreed that BG were supposed to replace the valves
anyway then get the idle buggers back to do the job they were paid for.

Tim

"JohnW" wrote

snip...

You may want to check the setting of the auto bypass valve. I had a
boiler replaced last year, and it looked like the installer forgot to
set up the bypass valve. This caused some banging when the stats
switched. I adjusted the bypass and it cleared the problem.

John

Seconded.

Although the poor setting of mine didn't initially cause banging - that came
later.
Because the by-pass valve never opened, the boiler went into alarm state
when all the zone valves closed.
Also the pump over-ran for ages to try to dissipate the boiler heat.

Banging started much later and was resolved (for now at least) by turning
off the system, winding the by-pass valve fully closed - then fully open -
then back to its correct setting.

Maybe it would be better to sling these things and just use the old
fashioned 15mm balance line to ensure some flow is maintained across the
boiler?

Phil

"TheScullster" wrote in message
...

"JohnW" wrote

snip...

You may want to check the setting of the auto bypass valve. I had a
boiler replaced last year, and it looked like the installer forgot to
set up the bypass valve. This caused some banging when the stats
switched. I adjusted the bypass and it cleared the problem.

John

Seconded.

Although the poor setting of mine didn't initially cause banging - that
came later.
Because the by-pass valve never opened, the boiler went into alarm state
when all the zone valves closed.
Also the pump over-ran for ages to try to dissipate the boiler heat.

Banging started much later and was resolved (for now at least) by turning
off the system, winding the by-pass valve fully closed - then fully open -
then back to its correct setting.

Maybe it would be better to sling these things and just use the old
fashioned 15mm balance line to ensure some flow is maintained across the
boiler?

Phil


Thanks for the idea's guys. The bypass valve (honeywell du144) is
set to the widest open position. At least I think so. The brass knurled
nut is fully anti-clockwise. FWIW I am also getting very long pump
over-run times. The boiler is set to 75c.

Can we rule out a faulty zone valve as the cause? My theory is that
the wet part of the valve is sometimes sticking when the motor is
deactivated,
but then the return spring wins the battle and closes the valve with a short
sharp shock. Most of the advice I came across in the web for
water hammer was to sort out the pipework but in this case the
pipework has been working for the last 10 years (or so) and the
water hammer only showed up ~6 months ago.

Thanks again....

"Tim Downie" wrote in message
...
snip

I wonder if you might have an old directional zone valve that has been
fittted the wrong way around? It may be that with a bit of slack
developing in the actuating mechanism, the ball in the valve is bouncing
on its seat?

Work out which way the water is flowing though your valves (feel for which
side heats up first when the system is turned on) and make sure that this
agrees with the direction indicated by the arrow (if present) on your
motorised valve.

Of course, if it was agreed that BG were supposed to replace the valves
anyway then get the idle buggers back to do the job they were paid for.

Tim

Tim, zone valve flow direction is correct. The system has been working
fine for many years. Thanks for the suggestion though.

p.s. I got a refund from BG for the zone valve installation that wasn't
carried out.

My worry is that BG is correct and my existing zone valves are just fine.

That leaves me wondering just what *has* happened with my system and
how to fix it.