Boiler locks out with E02, burner stops shortly after ignition or does not start, overheating sensation or very hot casing.

Safety first: Turn off power to the boiler and allow it to cool completely. Do not remove any covers that expose gas or combustion components unless qualified.

User-level checks:

• Ensure all radiator valves and any isolation valves on the heating circuit are open.
• Bleed radiators to remove trapped air; top up system pressure to the level specified on the Chaffoteaux data plate (typically 1.0–1.5 bar when cold).
• Press the manual reset on the overheat thermostat if accessible on your model (refer to the user manual). Then reset the boiler from the control panel.

Technical checks (for qualified personnel):

• Verify operation of the circulation pump: check that it runs on demand and that the pump shaft is not seized; free or replace the pump if necessary.
• Check for sludge or scale blockage in the primary heat exchanger; flush or chemically clean as per Chaffoteaux procedures.
• Test continuity of the overheat thermostat and replace if it is open circuit when cold.
• Confirm correct wiring and sensor readings to the control board (flow and return NTC sensors).

If E02 persists, the primary heat exchanger or pump may require replacement. This should be done by a professional heating engineer.