awo3560 fh

Cust says halfway through any wash error code fh appears. Had a look yesterday. Checked inlet filters, checked inlet pressure 3.5 bar cold, 1 bar hot. Valves were 3.5>4k. Pressure sw, chamber and tube ok. Only thing untowards was a noisy drain pump(working ok)I ran a short wash while there as I had d/washer to do also. It did not fault on me. Rang today saying it still doing it. Checked usual as well carbons and heater. Am thinking a sticking cold inlet valve but not sure. Any ideas.