Boiler intermittently overheats and shows E9 224, may be linked to pump or flow issues rather than pure sensor failure.

Safety first: Allow the boiler to cool fully before touching any pipework. Surfaces can be extremely hot.

Homeowner checks:

• Check pressure is correct and top up if needed.
• Bleed radiators to remove airlocks.
• Ensure all radiator valves and any isolation valves near the boiler are open.

Engineer checks:

• Confirm pump speed and operation; listen for cavitation or grinding noises and replace the pump head if weak.
• Check for temperature differential across the primary heat exchanger; a large difference may indicate blockage.
• Inspect and exercise the diverter valve to ensure it moves freely between CH and DHW positions.
• Consider a system powerflush and fitting of a magnetic filter to protect the Worcester boiler.

Overheat faults can damage the heat exchanger if ignored; professional attention is recommended.