Hotpoint DWF50 error code?

Hotpoint DWF50.

Water does not heat during wash cycle. Water empties and machine stops with the 'Delicates 50c' light flashing. ( the 'rinse aid' light is also flashing but it always does due to a longstanding fault so may be part of the error code or not).

I assume the error code is pointing to a failure to heat the water but does it point to something more specific.

I have the technical ability to carry out a repair but any assistance to diagnose the exact failing part will help.

Nigel