What does the Heatline F9 fault code mean?

Your boiler has switched itself off for safety because the water inside has become far too hot.

How much does it cost to fix Heatline error code F9?

Typical repair cost for the Heatline F9 fault is £100-280 including labour.

Check that all radiator valves are fully open to allow water to circulate.

Lock-out due to overheat thermostat activation on the outlet pipe.

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.

Work through these before the call-out.