Trying to repressurise my Worcester combi boiler.
I've done it a few times over the past few years with no problem.
This time - inserting internal filling key into the manifold, turning from open to closed, then turning the white nut to let the water into the heating system - but it flows out over my hand instead!
Same problem whether boiler power is on or off.
I'm probably doing something very basic wrong. Any ideas what?