Re: diplomat dishwasher
Your machine is a Smeg-built appliance and if it’s giving an E3 error as you suggest (1st two lights flashing, last one on constant) then there are several possible causes for the fault:
Faulty heater
Thermostat faulty/incorrectly positioned
Electrical connections defective/insecure
Spray arms obstructed/jammed
Faulty motor
Timer/programmer faulty
Without identifying the cause of the problem it could end up being expensive to start changing parts unnecessarily. You might be best getting in an expert to diagnose the fault for you.
If it’s the last two LEDs that are flashing then the board has defaulted to an unknown error code which isn’t related to any particular fault. Try running the machine again and taking note of the sequence of flashes before it changes to this: it sometimes changes to the two end lights flashing after it has been on another fault for a while.