Hello, I have a boiler heating system with 3 zones (top, main & ground floor). Recently the pipes began knocking loudly. I've watched a few videos on how to purge the air that's likely causing the noise. First turn off boiler, then shut off a zone's intake valve, manually turn on zone switch, attach hose to tap above zone intake valve, turn on tap, purge water & air, reverse process and repeat on next zone. However, there are no taps on the individual zones. There appears to be only one tap to attach a hose to, below the pump. There is however, another (flip?) valve on a pipe connected to a hose leading to the drain. Is this flip? Valve (shown near my knee in the pics below) possibly how this system is designed to manually purge air? Note, there is also an air bleeder valve - that looks like it’s seen better days and may be the root cause of the ‘new’ air issue. I did lightly tap this to possibly unjar the float that apparently can get stuck. Is there a way to tell if this is working? Thanks in advance!

Hi BSA

You attach a hose to the tap below the pump and then open each zone valve individually. Here, you'll bleed one zone at a time, close the zone valve and then repeat at the next one, etc. Make sense?