Coolant system over pressurizing

Had a head gasket failure, have replaced it along with thermostat and all relevant gaskets, the car runs as good as ever but there is still pressure building up in the coolant system enough to push it out the coolant bottle. There is no steam exiting the exhaust and no visible signs of an external leak, when started the top hose seems to build pressure but once the thermostat opens the hose goes back to a normal state, although if I put my hand to the top hose I can feel air passing through it which also shows in the ccolant bottle, as said the car runs great without missing or running eratically as I would expect with a gasket failure again or a cracked head, no hoses are split, the radiator which was the cause of the last failure was replaced so this is good.
i am hoping that you may be able to help me out as its really becoming a nuisance now.
oh its a 1.3 16 valve b3 engine I believe
thank you