I've unplugged the wire for troubleshooting now
Do you mean that you disconnected one of the heating element leads? If so, that's a good move. What makes you say that the autofill is not working? Correct water level in your boiler is ABOUT 4.5" as measured from the bottom of the boiler. You can check this with a 1/16" wooden dowel inserted down the hot water connection on the boiler.
With the machine off and unplugged, disconnect the probe wire's connection at the Gicar box and measure the resistance between the end of this wire & ground. I get about 22 mega ohms with the water not in contact with the probe and 0.6 mega ohms after letting the machine autofill.