[disclaimer: non-diy person, me]
I've recently moved into a mid-70s two-storey detached house. The house
has a new Worcester Greenstar C/H system, installed just before we moved
The problem is that first thing in the morning when the hot tap is
opened there is a LOUD noise like a hammer-drill from upstairs, lasting
for up to a minute. This only happens if the tap hasn't been opened for
several hours. If the tap is closed while this is going on, the noise
takes a couple of seconds to fade away. I can feel a couple of the pipes
in the airing cupboard vibrating strongly, particularly a flexible hose
that goes to what seems to be some sort of pressure vessel above the
The installer has been back and said something about air in the system
causing this problem. He reckoned that he had fixed it by doing
something in the loft (ball valve?) but the noise returned after a
couple of days. Before I call him back again can someone please give me
a clue as to what might be happening? Just to guard against bullsh^W
flannel, as it were.
On 15 Feb,
firstname.lastname@example.org (Sn!pe) wrote:
Wotcher doing out of the shed, tea room or pub?
I've had similar troubles with a conventional hot water system and a
combination of (hot) tap openings (and rapid closure) and bog flushes. This
was alleviated to some extent by introducing air /into/ the system to damp
resonances. On one occasion reversing a washer in the bog cystern cured it
for a while (moved the resonant frequency).
I suspect your water pressure is higher overnight and there is a non return
valve on the hot water system, thus holding teh higher pressure. The release
of this overpressure when you open the hot tap is setting up a resonance in
the pipes (AKA water hammer). A loose pipe may cause it. De-tuning the
resonance will cure it. Finding what is resonating can be the problem. In my
case it was started by flushing the bog followed by opening the loft tank
ball valve by running hot, and almost simultaniously opening and shutting
rapidly the cold tap, thus setting up two ball valves oscilating in
resonance. One of my offspring could tune this up to a grand finale. No-one
In your case you have a spring in the form of a hose, and another as an air
Reducing teh Q of the tuned circuits, by adding damping, or altering the
resonant frequencies/mutual coupling should cure the problem.
I leave this as an exercise in applied mathematics and lateral RF
Mine's one of the black stuff!
Mornin' Mr Thumbs. I'm here as an earnest seeker after truth and
enlightenment into the mysteries of plumbing, of course. Much as I love
the shed and so forth I find that one is more likely to get a sensible
answer in a technical group...
Ta for all that, I hadn't thought of it in terms of Q before. Thinking
about it, the solution proposed by RobertL of fitting a shock arrester
is vaguely analogous to connecting a decoupling capacitor to an HT rail.
On Feb 15, 10:38 am, email@example.com (Sn!pe) wrote:
Sounds exactly like waterhammer to me. You can fit little expansion
vessels that are specially designed to damp out this kindd of thing.
For example: the "shock arrester" about 1/3 way down this page.
I fitted one last month, the pipes were regularly banging here when next
door had a washing machine or something similar on. Made my mains inlet
bang throughout the house.
I fitted this just above the stop cock:
Not had any hammer since. It has an adjustable valve in it, pump it up
with a bike pump. Unfortunately, no instructions with it, but it seems
to work well as supplied.
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