Hoover Dishwasher Error Message E2; How do I progress this problem? ?

Error Message E2; is displayed, subsequent to the commencement of any wash cycle. An audible sound alarm sounds repeatedly and the wash cycle is not completed.
The instruction manual's solution is to "open the inlet hose."
At all times the manual isolation valve connecting the inlet hose to the appliance is open & allowing water to run through it.
The probelm seems to be within the internal pipework of the machine either a blocked filter or a electronic valve or its controller?
Any advice as to how to progress would be appreciated.