Hotpoint WD71P Error E11 Error Message?

My Hotpoint WD71P washer / dryer after 3 years or so of working fine now displays 10-15 minutes into every wash cycle a E11 Error Message (No hot fill). I have replaced the single inlet valve but to no avail, any ideas as to the next step? Is it likely to be a faulty thermostat, or what else could it be? After switching off the mains supply and reselecting the wash programme (once or twice) the wash cycle completes without failure.

Many Thanks
Kevin