This can be caused by either bad fill solenoid valve, or debris in the piping system of the fill line.

Run the sterilizer up to the operating pressure and temperature.
Turn the bottom knob to ‘fill position’.
Give it a minute or two for venting to complete.
This should blow out any debris in the line and solenoid.
If after doing this you still have the problem, replace the Solenoid.

Thank you –
~Shlomo Savyon
Your Sterilizer expert