I would love to know how the air gets to the boiler that causes these
problems - which are only when the system starts up in the morning.
Perhaps
there is some problem with the boiler itself??

Over the past year, my central heating was also making a real racket when it
started up causing the vertical pipes to rattle. I thought the pipes had
just come loose from their fixings (which they had).

However, last October the pump failed. The engineer came to replace it and
the new one is perfectly silent. He said that the pump failed due to air in
the system and that the central heating piping was incorrectly installed
causing air to be pulled into the system. This is maybe how air is getting
into yours. I'm afraid I can't remember which pipes were incorrect. He did
say that the pump's life would be reduced unless the fault was remided.

Regards, Rob.