Central heating bangs only when water goes off

[Birdbrainuk]

The central heating system heats fine but if only the water is on When it goes off the system bangs and the heating/water change over valve rattles this can all last for a minute or so.
If the heating is on then this does not happen. I guess there is air in the system but what is the best way as it does not seem to be air in the radiator I have aleady bled them.

Hope someone can help with this

 

[ianmcd]

what make and model of valve do you have ?

 

[Birdbrainuk]

Valve is a honeywell 40003916-003
Power head for motorized valve

Hope this is what you wanted