Thank you for the reply. I think I am missing something though. I take it the small expansion tank you mention is inside the boiler? I am not understanding which tank to look for to find the 15mm pipe you mention.
I only have a cold water header tank above the hot water tank.
I am still...
I am planning on swapping my old Glow-worm boiler for a combi boiler. This is part of a bathroom refurb project to get rid of the old airing cupboard which houses the hot water cylinder and cold water header tank.
I will be getting a pro to do the boiler swap, but I will be doing the bathroom...