Boiler locks out with E02, burner stops shortly after ignition or during operation, possible overheating sensation on casing.

Safety first: Switch off power to the boiler and allow it to cool completely before touching any pipework. Do not repeatedly reset an overheating boiler.

User checks:

• Check system pressure on the gauge; if below 1.0 bar, top up via the filling loop to 1.2–1.5 bar when cold.
• Bleed air from radiators using a bleed key, starting from the highest radiators, then recheck pressure.
• Ensure all radiator valves and any zone valves are open to allow circulation.
• Reset the boiler and listen for the internal circulation pump running; if it is silent or noisy, a technician is required.

Technician checks:

• Inspect and test the overheat thermostat / safety limiter mounted on the flow pipe or heat exchanger; replace if faulty.
• Check the primary heat exchanger for scale or sludge blockage; flush or chemically clean if necessary.
• Verify operation of the circulation pump (Termet OEM pump or Grundfos/Wilo equivalent), checking for seized rotor or blocked impeller.
• Confirm correct readings from the flow and return NTC sensors and replace if out of tolerance.

Do not operate the boiler with a known overheat condition; unresolved E02 faults must be handled by a qualified heating engineer.