"Johan" wrote in message
...

Hi,

Not a regular poster, but often read this newsgroup.

I have just replaced some of my cold water plumbing, and now seem to
have a problem with the combi boiler: whenever I close a cold water tap,
the boiler sounds for a few seconds as if it is about to turn itself on.
This also happens when a toilet has been flushed, and the water flow
stops. The boiler is on the first connection to the mains water. The
mains pressure is fairly high (lead pipe from the street to the house
replaced last summer). I cannot think what I have changed that caused
the boiler to do this. I used speedfit pipe and fittings (yes, I have
read lots about those on this newsgroup; I find them very easy to use).

I was old a 'hammer arrestor' would solve my problem, but this has not
worked (the one I got is made by Sioux and on the packaging it states it
will keep the pressure below 10 bar; seems a bit high to me).

Is it possible that cold water is forced into the boiler when I close a
tap, which makes the boiler 'think' a hot tap has been opened? At what
pressure would this happen?

Any suggestions on how to fix this problem?

Many thanks in advance,

Johan

It could be that through the combi when a tap is opened the pressure becomes
negative in relation to the rest of the cold water pipework. When you close
the tap the pressure increases in the pipework and moves across the combi
and activates the flow switch, or the 3-way valve. What make of combi, they
don't all work the same way?

You could

1. Insert a none return valve just before the combi. Then this will not
allow pressure to lower inside the combi and hot water pipework.

2. Take the combi cold feed right back to the stop cock, making this supply
dedicated to the combi only. Have the cold water taps tee off this pipe at
the stop cock.

Try No. 1 first.



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