Boiler or pipes STILL banging when CH is cooling down,any ideas?

[jonkaw]

I posted in summer as HW system banged when cooing down it is now even worse once CH is cooing down but it's common between both systems any ideas folks, desperate now.
Potterton combi boiler 10 yr old inherited 4 yr ago when I bought house, no issues until earlier this yr.

 

[Last Plumber]

Expansion and contraction of pipes?
Are they plastic or copper?
One common cause of cracking/banging in walls and under floors etc, is plastic pipework incorrectly installed.

 

[jonkaw]

Expansion and contraction of pipes?
Are they plastic or copper?
One common cause of cracking/banging in walls and under floors etc, is plastic pipework incorrectly installed.

They are all copper and have not been disturbed by me. But could be possible hard to tell where banging comes from.
Been ok for last 4 yrs I've been in the property