Renault Espace 1998 2 point 2 turbo diesel and the heating system is not working due to an airlock or so the garage says can anyone advise you how you clear this airlock and get the heating working?

There's a knurled screw about 1cm diameter on a heater pipe near to the battery. Unscrew this to release air in the system. (Unfortunately the 'O' ring that seals it can rot and break - make sure you have a spare)