FP GW709AU stops filling

Hi there, just joined, my GW709AU has developed a fault where it starts filling, cold wash only, cold water only connected, then stops, and after some time, brings up a fault beeping, the cold and hot LEDs are flashing. There is nothing wrong with the inlets, not blocked, water pressure OK etc, does the same if I swap to hot solenoid and hot wash, turn off at power point, back on and it will fill and run through complete cycle OK. I have tried the diagnostics, but must be doing something wrong, I get no fault code LEDs lit.

Thanks 🙁