F13
Saunier Duval
External Sensor / Cylinder Probe Fault
Boiler shows F13 and will not operate, often after wiring changes or accessory installation
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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.
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Possible Causes
Faulty external temperature sensor, Faulty cylinder NTC probe, Incorrect sensor wiring to PCB, Sensor short or open circuit
How to Fix / Troubleshooting
Safety first: Turn off power before working on sensor wiring.
Steps to check:
- Identify which external sensor is connected (outdoor sensor, cylinder probe) according to the installation.
- Inspect the cable from the sensor to the boiler for damage, joints, or water ingress.
- Check that the sensor is correctly connected to the designated terminals on the PCB.
- Measure the sensor resistance and compare with Saunier Duval charts for the measured temperature.
- Replace the sensor if readings are out of range or intermittent.
Warning: Incorrect sensor wiring can affect boiler modulation and safety. If unsure, call a professional.
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Repair Difficulty
Medium
3/5
Required Part
External Temperature Sensor / Cylinder NTC
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