Water hammer /Combi Boiler - Please Help

Recently had a new combi boiler installed but had problems with water hammer ever since. Pipes rattle around the house and it can be stopped if you muck around with the thermostat valves on 2 radiators above the boiler., In the main however I need to go to the boiler switch it off and switch it back on. It appears only one large pipe rattles but there are about 8 pipes in a row and it looks complicated! Even when everything is off in the middle of the night the water hammer can occur. I think there is a header tank in the boiler (saunier duval) that comes on and off every so often and when it does the pipes rattle to drive me MAD!!! The Plumber has been round few times and put in loads of pipe clips and the Boiler engineer says there is nothing wrong with the boiler.

Can anyone out there please help????? I have read a lot about the water hammer arrestors. Would they help? If so where would they need to go?

It is possible you might have the thermostatic valves fitted the wrong way round. This can cause a resonance in the pipework.

Thanks for the reply Simon.

Being new to this plumbing malarky - do you mean the thermostatic valves on the radiators?

As the problem occurs when the central heating is off I would have thought i could elimate the radiators?

When it happens in the middle of the night it appears that it is the boiler clicking (well Thumping) on and off and causing reverberation in the pipes. It happenned twice last night 1am am 3am - and I need sleep!!

Please help.

Call the manufacturer then. The installer's had his chance!

Hello again,

How would I know if the Thermostatic Valves were on the wrong way round please?

Most will have an arrow on them pointing in the direction water should flow round, turn the heating on and whatever pipe at the rad heats first is the flow make sure the heats moving from the flow to the return in the direction of the arrow.


but now this has been brought up, the ones BG use are bi directional so have 2 arrows on them, thus I assummed they could be fitted either way, but im now told no theres still a certain way to fit them, can anyone clear that up?

Thanks guys. Plumber called back and is going to check. Will lt you know.

Anything else worth checking out that could cause water hammer?