What is this part of my CH plumbing?

[nads1978]

The copper part being pointed to by the red arrow.

The bottom pipe comes from my oil boiler, the middle one is to the pump, the top one disappears in my ceiling somewhere.

Thanks.

 

[45yearsagasman]

That's called an air separator and it helps to remove bubbles of air from your system. They go up the open vent to the feed expansion tank in your loft.

 

[nads1978]

Groovy, thanks chap!

 

[45yearsagasman]

Welcome.