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

[Rickyy]

Does your boiler have a hot water preheat function? Could be that kicking in early in the morning?

What make and model is it?

[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.

[Gingerbread Man]

Frost stat???

[Craigybaby69]

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

[Rickyy]

Craigybaby69 said:

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

You may have one fitted and its firing the boiler in the early hours.

Some have internal frost stats and fire themselves up if the system water gets too cold.

If you have a programmable room stat, it could be that you haven't set the overnight temperature low enough and its kicking in.

I had mine programmed to be 15 degrees C overnight and the house would fall below that some nights, so the heating would kick in and wake me up.