Boiler increasing in pressure overtime?

Worcester Bosch 28cdi increases in pressure overnight on its own. Followed a refill YouTube video, which increased pressure, but the white key underneath just spins around and I can't get it out either. Ive tried turning the grey/white flow screw clockwise, but doesn't seem to do anything. Has an expansion vessel fitted on one of the pipes. The downstairs kitchen rad doesn't get warm unlike the rest of the house. Neither does the pipes off it.

Advice from 1 local tradesperson

Depending on system that you have either a system boiler or combi there could be either a cold water back flow into the heating mains issue or your expansion vessel is losing its charge and making the system pressure rise or it’s a cold filling loop left open slightly allowing water to trickle in

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