The Kenwood KDW60X10 shows the E4 code when there is a water leak or a problem with the float switch (or it's PCB board connection). This could be a leak at the tank, the hose, or that the drain pump's anti-flooding system has been tripped.
Disconnect the dishwasher from power and the water line. Look for signs of a water leak under the unit. If the hose is leaking, you may be able to replace or reseat the drain hose. (Also make sure that there are no kinks in the hose.) Note: sometimes the leak is in the plastic where the drain hose connects to the dishwasher. That is harder to fix.
If the tank is leaking, replace the entire unit. For the other possible problems, you should consult a repair tech to narrow down the issue. Float switches are easy enough to replace; the PCB board and the anti-flooding system are not as easy to reset.
The manual for your dishwasher is available here: http://www.partmaster.co.uk/company/partmaster/manuals/Kenwood%20KDW60X10.pdf
I hope this helps.