What does the Vaillant F.23 fault code mean?

Your boiler has shut down because the internal water temperature is rising too quickly or unevenly, usually due to a circulation blockage.

How much does it cost to fix Vaillant error code F.23?

Typical repair cost for the Vaillant F.23 fault is £120-350 including labour.

Check that all radiator valves are fully open

Safety switch-off: Temperature difference too great (NTC1/NTC2)

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Each noise points to a different fault.

Sludge build-up — needs flushing, not bleeding.

7 signs repair isn't worth it anymore.