Noisy central heating pipe when cold

[Craigybaby69]

Hi folks, there are loads of threads on various websites that describe noises when the central heating starts up....however, what could be the cause of a metallic sounding clonk between 2 & 5 am when the central heating has gone off at 10pm....do CH pipes take a long time to cool down and when they finally have the noise is a pipe contracting?
Many thanks .
Craig

[Craigybaby69]

Hi, thanks for reply, don't think it has that function or need it as its a baxi combo condensing and it's only started again this week with the heating going back on.

[Craigybaby69]

I'm not with you, are you saying I should get one or asking if I've got one fitted?