Hello, Thankyou for the prompt replies, I belatedly found the vent on top of the sand filter and have proceeded to vent the air, this appears to have removed some of the air . However after running the pump for a period of two or three hours the air seems to come back. I don't appear to be losing pressure on the "manometre" , if anything it seems to working better. Do I continue with this method, or should I begin to work back from the pump until the pool? I suppose I will have to start the process of removing the paving stones to see if I can get access to the pipes, when the air bubbles blow into the pool, they seem "clean" so I hope the air leak is more centered on the pump. Thanks again for any ideas, like all things the pool is great when working and being our first year with a pool, I am on a steep learning curve. For information, the pool was constructed about 20 years ago, it is a concrete pool (11x 5m) and holds around 80m3 of water. FC Moux