Air gets into the pump after the initial fire up which stops the pump circulating water. Everthing works and the rads get hot, but then air gets into the pump and stops circulation after this initial fire up. My CORGI registered boiler man came out yesterday and confirmed there is nothing wrong with the Potterton boiler (even though it is over 13yrs old) a new pump has been fitted, all rads have been bleed and the whole system has been flushed and back flushed. He confirmed the system is clean. In the whole 13yrs of living here nothing has been altered; something has happened and I cannot find out what that is. Can anyone help please?