Boiler shows E05, no heating or hot water, temperature reading may be unrealistic (very high or very low).

Safety: Isolate power before accessing internal components.

• Locate the flow NTC: Remove the front cover and find the flow temperature sensor clipped or inserted into a pocket on the flow pipe leaving the Defro heat exchanger.
• Check connection: Ensure the NTC plug is firmly seated on the sensor and on the control board. Look for signs of corrosion or water ingress.
• Inspect cable: Follow the cable from the NTC to the Defro PCB, checking for cuts, pinches, or burn marks.
• Reseat sensor: If the sensor has come out of its pocket or lost contact with the pipe, reinsert it fully and secure any spring clip so it is tight against the pipe.
• Reset boiler: Restore power and reset. If E05 persists, the NTC sensor should be replaced with a genuine Defro flow NTC of the correct value.