E13 error; controller indicates lambda sensor or O2 regulation fault (on Defro models with lambda control)

Safety: Allow flue and sensor to cool fully. Disconnect power.

• Locate the lambda sensor threaded into the flue or combustion chamber outlet.
• Inspect the sensor cable and connector for heat damage or loose pins.
• Do not clean the sensor with chemicals or abrasives; if heavily contaminated with soot or ash, it may need replacement.
• Check that combustion settings and fuel quality meet Defro's requirements; poor fuel can shorten sensor life.

Lambda sensors are precision components; diagnosis and replacement are best handled by an authorized Defro technician with the correct calibration tools.