F4 means no drain detected
in the time allowed.
Does the machine drain the water out or not?
If NO, in order of easyness (Is that a word? It should be...), the machine may have a blockage. If you can hear the drain pump running, start with the sink coupling - is the spigot blocked? If you can't hear the drain pump running, there is probably a foreign object in the drain pump jamming it. With the power off, remove the lower cover plate - the drain pump is at the front and is a twist fit to remove. BE CAREFUL - Whirlpool employed some of Wilkinson Swords finest engineers to ensure that the edge of the undertray is honed to a killing edge. The drain pump itself may have failed, but that's unusual.
If YES, the machine is not detecting that the water has gone. Remove the filters in the centre of the base of the machine and look at the 3 o'clock position in the hole revealed. You will
see a black grid. This is prone to choking with fatty deposits. You can use plenty of hot water and an old toothbrush to try and scrub it clean. If that doesn't do the trick, it's a twist fit from underneath to remove, then try cleaning it. Commonly, the microswitch on the back of the unit fails and simply doesn't switch over, in which case, you'll need one of THESE
Stay safe, power off at all times.