On Sunday, March 25, 2018 at 5:38:57 PM UTC+1, RJH wrote:
Can anyone identify this noise? -

https://drive.google.com/open?id=1o_...flq4qiwX_jS6vh

It's a sort of high pitch metallic rattling, happens all the time, and
has started since I drained and refilled the closed combi system.

--
Cheers, Rob

Is there an air vent on the water circulation pump? Maybe it needs bleeding. If it's an automatic one (with a float inside) they sometimes clog up with limescale.

Robert