I have a similar machine with the same problem. Cold water valve opens during diagnostic but does not open during normal cycle. I suspect a semiconductor that is on the cold water valve circuit on the control board is experiencing partial failure. (The switch to the valve is electronic, not a relay.) Will replace it this weekend and see if that fixes the issue. These semiconductors wear down - and since cold water is used more often than hot, it might make sense that the cold water one wore out first.[br]
Why does it work on diagnostic but not on normal cycle? I'm not sure - it was suggested that the control board sends a weaker signal during the normal cycle and the gate sensitivity on the semiconductor has drifted with wear. It's an $0.82 part - definitely worth a little desoldering/soldering to test out the theory.