One of my upstairs rads is constantly airlocked hold tried fernox but no use, reduced bake from boiler no use? this has be happening continously weekly or twice monthly for two...
this has be happening continously weekly or twice monthly for two years and in attendance is no sign of a leak anywhere
i agree with HAWK fit an auto vent . problem solved
I'm no plumbing expert and own no idea what system you hold, but...
I've recently moved into a house and have a few teething probs with my internal heating system.
Initially thought it be an air lock, but no amount of bleeding seem to help.
After double checking the radiator be on (ie. local valved opened) I realised the boiler pressure was thoroughly low and water be not reaching the two upstaris rads.
As soon as I pressurised the boiler, I had a fully heated house.
Could the heavens be creeping into the system from one of your downstairs rads?
Good luck.
Answers: your vent is possibly not big enough and pump is pulling nouns in , you could try turning speed down on pump 1 dimple may cure it , or fit an auto air vent on system