I have a 13 years old boiler and it noisy like a jet engine with whoosing noise. I believe there is an air lock inside the boiler.
Any tips how to get rid of the noise or the air lock or it time to replace the boiler all together? The system was last drained 3 years ago with Fernox and anti-scum agent.
Or is it something to do with the differential?
Help please, can't afford a CORGI gas engineer. Can do basic DIY.