TD5 cooling system problem

Hi there just thought I would say hello to all, been looking for answers to my 2000 td5 Auto with 105,000 on the clock playing up with the cooling system, thought it was a airlock after filling with new antifreeze this year but I think it is now looking like HEAD GASKET as the posts I have read have pointed me in that direction. It does not over heat, pressurized top hose, water level drops in header tank when under pressure and having to rev the engine to get the heater to blow hot no creamy oil and had a sniff test carried out on the coolant which was negative.
Has anyone got any other ideas I would be grateful for any help.