Agile - what I mean is if a nut as in my case, is not tightened fully, then when the system is on and the pump is running - air may be drawn into the system via the loose radiator nut/joint, etc.
I had a towel rad fitted about 16 months ago and it kept getting air in like yours. The fault was one of the top 2 connections, plug and vent (at the top of the rail either side) were not fully tight. The were screwed in (have a rubber o-ring/washer on them) and not 100% tight.
Thank you both for your help with this query and your replies.
I have one further question though; I have heard that turning off the boiler valves to drain the boiler can often cause them to leak when re-opened. Is this very true or a myth?? If so is there anyway to stop the leak or any...
Can someone please answer me this regarding a combi boiler: when the gauge reads 0 pressure (0 bar) on the dial, does this mean the boiler is empty or the system is empty up to boiler height/level? To be clearer what I mean is, if I want to drain water from my system to replace a faulty air...