Trying to remove air lock from Trianco Eurostar50/70 oil boiler. ?
 
                Stupidly let heating run dry. Can see air in tubes, just can't work out where the release is. Have looked at manual, clear as mud. There is a square bit saying +Air-. Is that it? Should I be using an alan key or a screwdriver? TIA!
            
             Jane
            
 September 2015