thanks all, i will start inspecting the pipes in more detail.
The pump only comes on once every 1-2 hours so its a slow leak but its just not obvious as the water is in the bilge but no obvious route!
the aft cabin is dry, the heads are dry so its got to be a join between the aft cabin and heads / galley.
The hot water tank under the aft cabin is bone dry too so i think the relief spring is fine, along with the usual stern shower
the water gathers in the bilge in front of the steps and goes to the next one with the bilge pump in via the connecting holes.
of course no taps on and no water so i know its not rain water at least