Vaillant F.73 Fault Code

What causes the Vaillant F.73 fault?

This fault occurs when the boiler's internal computer receives an electrical signal from the water pressure sensor that is outside of its expected operating range. The most common reason is a physical failure of the sensor itself, though it can also be caused by loose or damaged wiring that prevents the sensor from communicating correctly. As a safety precaution, the boiler stops running because it cannot confirm there is enough water to operate safely.