Glow-worm Return temperature sensor fault

F7 error, furnace may overheat quickly or show incorrect temperature readings

Safety Warning

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

Defective return NTC sensor, Wiring fault between return sensor and Glow-worm PCB, Sensor not in good contact with return pipe, Moisture ingress in sensor connector

How to Fix / Troubleshooting

Safety: Turn off power and allow the system to cool.

Technician procedure:

Identify the return NTC sensor on the return pipe entering the heat exchanger.
Check that the sensor is firmly clipped to the pipe with thermal paste or good contact.
Test resistance of the NTC and compare with manufacturer’s chart.
Inspect wiring and connectors for damage or corrosion; repair or replace as needed.
Fit a new Glow-worm compatible return NTC sensor if faulty.

Repair Difficulty

Medium 3/5

Required Part

Return Temperature NTC Sensor

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