Miele inlet/drain red light?

Our machine is a Miele g64c plus. The inlet/drain light comes on for no apparent reason either right at the begining of the cycle e.g. 20 or so seconds after it starts or...more infuriatingly just close to the end of it's cycle ie when it is full of "clean"(ish) dishes and is just about to dry them; leaving the machine full of very hot water and steamed up dishes. Any ideas please? I am quite technically minded (very safety conscious) and able to take things to bits... and even "put them back together"....sometimes:)!!