On certain Indesit washing machines (and Hotpoint), if the on off light is flashing 3 times, with a slight pause, followed by flashing a further 3 times, or if it is displaying F03 you have an error code that is explained as follows –
NTC fault – check Thermistor and module connections
The NTC is the thermistor, which is a modern-day thermostat. However, as this fault is exactly the same as the Hotpoint error F03 please read the advice on that article Hotpoint WD washer dryer flashing lights – error code F03
Buy New NTC Thermistor or thermostat
Try Ransom Spares site for Washing machine NTC sensors & thermostats
Or see What is an NTC and how to test one
Many faults are best dealt with by an experienced repairman with the right tools and test meters. 
Find appliance repairs – Book washing machine (or other appliance) repair
c johnston says
good explanation very useful
R. Richardson says
Just what I was looking for easy to understand explanation and very helpful, thank you