Your boiler thinks a flame is still burning even after it has been told to turn off, which is a safety conflict that stops the system from running.

CH flow sensor fault: CH flow sensor (8000 - 20000 ohms at room temperature), Wiring and connections to sensor.

What causes this fault?

This fault occurs when the boiler's internal sensors continue to detect a flame or electrical current even after the gas valve has been closed. The most common cause is a carbon-clogged sensing electrode sending a false signal, but it can also be triggered by a fault in the main control board or a short in the internal wiring. Because it is a safety concern for the boiler to 'see' fire when it shouldn't, the system shuts down completely to prevent damage.