1998 renault clio 1.2 d type engine?

i was loosing water but dont no where from, put in rad weld, now water when gets hot blow back into exspansion tank, but radiator is still cool, i have blead radiator and heater but still happens, the colour of oil has no signs of water so i think head gasket is ok, would it be the water pump or thermostat.

Brian
February 2010