How to replace the WASH CYCLE SELECTOR KNOB - on an Ariston AV 105 Washing Machine

Either the knob or the switch is faulty. Can you pull the knob off and see if you can set the program with pliers on the shaft?

try to replace the circuit

it sounds like the nob is striped try replacing the knob.

According to the instruction book - it appears the machine has been stopped mid cycle then re-started.
Switch machine off, turn control knob to a solid circle symbol (they are after every set cycle). Switch machine back on and lights will flash and program is reset. You can then select wash cycle as normal.

The cycle selector is not engaged onto the timer shaft. Need to remove the on/off knob by removing the plastic "U" clip. Remove the cycle selctor knob and check that the steel spring clip on the selector is fully seated. Re-install the cycle selector onto the timer shaft aligning the selector key with the with tthe notch on the timer shaft. Re-install the on/off knob.

The cycle selector and on/off combination is a poor design. Users press the on/off knob in and turn clockwise to set the wash cycle. If you're not gentle this action wears the teeth on the timer shaft and the user has to press harder and harder to set the wash cycle. This pressing causes the cycle selector to be pushed off the timer shaft and you can no longer operate the machine.

VERY IMPORTANT:
Stop using the on/off knob to set the wash cycle. Press on the cycle selector to set the wash cycle. Use the on/off knob only for starting or stopping the machine. Don't press or pull too hard on the on/off knob or you will wind up pushing the cycle selector off the timer shaft.

pump blocked - clean out pump/filter/oultet hose. power off

try manually moving the knob through each cycle until it gets back to the finished cycle. or the timer may need to be replaced

i know it sounds simple but have you checked the filter and also check for foreign objects in the pump impellor

open the filter on the bottom of the machine (water will empty out).  Clear any blockage. 

Do you have the "easy iron" feature on? If so, the clothes will stay in water until you manually rinse it.