Loud noise from Radiators 45 mins after system switches off

Approximately 45 minutes after the central heating switches off at night (we have it set to switch on in the morning and stay on all day until 23:00 hours), a very loud bang and shuddering emanates from the radiators for a few seconds only. This is since we had a new boiler fitted, a Potterton Suprema! On occasions after manually switching off the central heating during the day time, the problem results, on queue, approximately 45 mins later. Possibly associated with cooling? But why?
Help please, anyone?

Hi,

I`m no expert so wait for somebody with more experience to reply before taking this on board BUT!

It sounds as though your pipework is contracting (after expanding with the heat flowing through it). The noise will be as the pipework rubs along a joist or where a bend is cut in to a joist etc.. the wood against copper causes friction as it expands/contracts and makes a noise which is then echoed through your radiators and pipework.

I`m surprised you don`t hear it when the system is heating up too.

Try locating roughly where the noise is actually from and then lift the floor boards and pad the rubbing areas with something to stop the rubbing.

Hope this helps.