Boiler displays A09, return NTC fault, may cause incorrect modulation or lockout.

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

Failed return NTC, Loose sensor, Wiring damage, PCB input fault

Safety: Isolate power before working on sensors.

Inspect sensor: Check that the return NTC is properly attached and not corroded.
Measure resistance: Replace the sensor if readings are not within specification.
Check wiring: Repair or replace damaged cables and connectors.
PCB diagnosis: Replace the PCB if the fault persists with a known-good sensor.

Medium 3/5

Return NTC Sensor

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