F15
Saunier Duval
Overtemperature or temperature differential fault
F15 error, often associated with very high or very low outlet temperatures
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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
Severely scaled primary heat exchanger, Blocked plate heat exchanger (on combi models), Faulty NTC readings, Low water flow through heater
How to Fix / Troubleshooting
Safety first: Isolate power and water. Allow the unit to cool fully.
Steps:
- Check flow rate: Ensure adequate flow at the hot tap. Clean or replace clogged aerators and shower heads.
- Inspect filters: Clean any inlet strainers or filters on the cold water inlet to the heater.
- Descale heat exchanger: If the unit is older or in a hard water area, arrange for professional descaling of the primary and, if present, plate heat exchanger.
- Verify NTCs: Check that all temperature sensors are correctly mounted and functioning.
Warning: Overheating can damage the heat exchanger and other components. Do not ignore repeated F15 errors.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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