"Aidan" wrote in message
oups.com...

shamblesforge wrote:
I`ve just changed my noisy Central Heating pump with no problems, but
have noticed a brass fitting located at the end of a copper pipe
coming from the pump .

It`s a 1" brass cylinder with a knurled screw end with a red plastic
unscrewable cap on top.

Automatic air vent. There is a float inside it which seals the outlet
when it is full of water. Air should be released on unscrewing the red
cap, providing there's air in the system. The red cap should be screwed
down a week or two after filling the system and no more air is in it.

The above concise reply should be on uk.D-I-Y plumbing/heating/FAQ.