I live in a small bungalow. It is fitted with a full flow CH/HW system. There is air in the HW side but I cannot find any leaks. Boiler oil fired, outdoors, Grant 50/70 new Oct 2004. New pump fitted recently no leaks and joints and valves (pump in/out) sealed with rubberised compound for added measure. Pump in loft about 10 feet above boiler. Discharge to 3 way valve. When CH only all is fine and quiet. When HW demanded air rushing around system. Vent to header tank from junction 2 feet before pump inlet. Automatic vent on inlet to HW tank. Header tank feed connected to HW tank return. HW tank return and CH return join somewhere before boiler behind plaster board panels. Please will someone advise what I should do?