Boiler intermittently locks out with E11, especially when heating is on for long periods.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Faulty return NTC sensor, Loose sensor connection, Damaged wiring harness, PCB sensor circuit fault.

Safety first: Isolate power before removing any covers.

User checks:

Reset the boiler and monitor if the error appears only under certain conditions (e.g., during long heating cycles).

Engineer checks:

Locate the return NTC sensor on the return pipe to the boiler.
Measure resistance at ambient and operating temperatures; compare the readings with Potterton charts.
Inspect wiring and connectors for corrosion or mechanical damage.
Replace the return NTC sensor if its readings are inconsistent or out of range.
If the sensor is OK, test continuity to the PCB and evaluate the PCB input.

Correct sensor diagnosis prevents unnecessary PCB replacement.

Medium 3/5

Return NTC Thermistor

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