On Mar 18, 7:26 am, Dave Fawthrop
wrote:
I have just had a new Combi fitted to the old *single pipe* radiator
system. Two zones upstairs and downstairs controlled with valves. It
worked fine.

The downstairs valve was in the wrong place so I drained the system and
moved it. Crossed a thread and had to replace it with a different make.
Refilled, bled radiators, and adjusted CH pressure to 1-2 bar.

Now the problem! The system gives a *single* bang a few times a day, at
random. Random events are a pig to fault find. It sounds to me as if it
*could* be water hammer caused by the valve closing. It really does not
sound like a gas explosion, just the pipes reverberating.

What do people think? What is a good method of fault finding?

Google giveshttp://www.water-hammer.com/

A US site says that air chambers are no longer recommended.http://www.builderswebsource.com/tec...aterhammer.htm
High temperature sealed are filled bladders?
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Do a basic check before anything else................. make sure you
have fitted the replacement valve correctly. On the brass body on the
underside you will see the letter A on one port and B on the other
port. Make sure water is flowing in the direction of A to B.