How can I fix water expanding in header tank, Ford Escort TD?

Have changed head gasket three times to alleviate back pressure in header tank but problem still occurs. First gasket blown between one and two bore hence no compression and no start no drive. Second gasket put in car, starts well and drives well, does not overheat but pressurises up and blows water out of header tank. Third time changed thermostat and gasket but still same problem. Followed full instruction from Haynes manual. 1995 Ford Escort TD 1.8.