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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Are The valves motorised? If so do you have a two seperate
thermostats, one for upstairs and one for downstairs? Does your new
combination boiler have in integral bypass if not then there is your
problem. As both the valves close the water has no where to go hense
the banging. You will need to fit an AUTOMATIC bypass between the flow
and return pipes. Usually in 22mm and a certain distance from the
boiler depending on the size of your system this will be explained in
your installation manual. You will need to set the bypass so it gives
a minimum flow rate when both valves are closed which will aslo be in
the installation manual.

Hope this helps