Boiler locks out with E02; no heating or hot water, internal overheat light may be on.

Safety first: Isolate electrical power to the boiler. Allow the boiler to cool fully (at least 30–60 minutes) before attempting any reset.

• Check system pressure and air: Ensure the heating system is properly filled and bled. Air pockets can cause local overheating in Elnur electric boilers.
• Inspect circulation pump: Remove the boiler front panel (if competent and permitted). Locate the circulation pump. Check that the pump shaft turns freely by using a screwdriver in the pump vent plug (if accessible). A seized pump will cause rapid overheating.
• Reset the high limit thermostat: Locate the manual reset overheat thermostat on the primary flow or heat exchanger. Press the small reset button until it clicks. Do not repeatedly reset without finding the cause of overheating.
• Check for blocked heat exchanger: Look for signs of sludge or scale in the primary circuit. If the boiler overheats quickly after reset, the heat exchanger may be restricted and require professional power-flushing or replacement.
• Restore power and test: Turn power back on, call for heat, and monitor temperature rise. If E02 reappears, stop using the boiler and arrange for a qualified technician.

Warning: Persistent overheat trips indicate a serious circulation or control fault. Do not continue resetting without repair.