Volvo FM11 Euro6 cooling system pressurising

Anybody any ideas on cooling system pressurising on my 2016 Volvo FM11.
I have had Injector Sleeves replaced, also replaced compressor with brand new one.
It has passed on combustion test but still pressurising and losing water out of the header
tank overflow pipe mainly when loaded.

If you’re certain that there is no leakage of cylinder compression/pressure into the coolant system a knackered water pump can cause similar symptoms if it’s not circulating the coolant well enough.