Sounds like air rushing around CH pump

[mesteptoe]

Just noticed the sound of air rushing around my CH pump. It's an old system and has never given any trouble. There is a vent in the system above the level of the pump. I have undone the screw on the top of the vent but nothing comes out, not even water. The style of the vent is like the Intervent model. I am not sure whether the vent needs an overhaul. If so can it be taken apart without draining the system.

Also can the pump be vented by turning the central screw?

All advice welcomed.

Thank you.

 

[BingoBongo]

open the screw on the pump but be prepared for some dirty water

i would also check your header tank or system pressure to make sure there is water in the system

 

[Nige F]

do these things with the pump switched off