Boiler displays F22 and will not fire; pressure gauge often near zero.

Safety first: Ensure the boiler is cool before adding water.

Steps to check:

• Check the pressure gauge. If below 0.5 bar, repressurise via the filling loop to 1.2–1.5 bar.
• Bleed radiators and top up again if pressure drops.
• Reset the boiler and check for normal operation.
• If the gauge shows correct pressure but F22 remains, the pressure sensor may be faulty and require replacement.

Warning: Do not run the boiler with no water; this can severely damage the heat exchanger.