Thanks chaps, appreciate the input.
David - yes, valves to port, starboard and bow.
Its still up at pretty much the same pressure now for 16 hrs so it is odd. I'm out again Saturday so will see then and be sure to take the pump with me, as you all know the effort in getting everything ready and going out (dragging the family
) means the last thing you want is issues on the water.
I've checked all the outer valve rubber seals - all good and in perfect working order. Trying to manually 'flex' or distort the valve housing causes no leaks.