Display shows E02 and water temperature is erratic or unit shuts down

Safety: Isolate electrical power at the fused spur and verify with a tester before touching internal wiring. Allow the cylinder and pipework to cool.

Diagnostic and fix steps:

• Locate return NTC: The return temperature sensor is usually fitted on the primary return pipe or in a pocket on the lower side of the Gledhill cylinder. Refer to the schematic on the casing.
• Visual inspection: Check that the sensor is firmly clipped or inserted, not hanging loose. Look for crushed, cut, or heat‑damaged cable insulation.
• Connector check: Unplug the sensor from the PCB, inspect for corrosion or bent pins, then reconnect firmly.
• Measure resistance: With power off, measure the NTC resistance. Compare with the expected value for the ambient temperature (e.g. ~10kΩ at 20°C). If the reading is far outside spec, replace the sensor.
• PCB check: If a new or known‑good sensor still gives E02, the PCB sensor input may be faulty. Inspect for burn marks or water ingress. PCB replacement should be done by a competent person.

Note: Always refit any insulation around the sensor pocket to ensure accurate temperature readings.