E5
Saunier Duval
Power Supply Instability
Thermostat shows E5 and backlight flickers or unit restarts randomly
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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 230 V to low-voltage power adapter, Loose low-voltage connector at thermostat base, Voltage drops on boiler internal supply to thermostat, Short circuit on thermostat PCB drawing excess current
How to Fix / Troubleshooting
Safety: Turn off mains power before handling any 230 V adapters or boiler connections.
- Check adapter: If your thermostat uses an external plug-in adapter, test it with another device or measure its output with a multimeter. Replace if voltage is outside the specified range.
- Inspect connectors: Ensure the low-voltage plug is fully inserted into the thermostat base and that screw terminals are tight.
- Boiler supply: If powered from the boiler, have a technician verify the boiler's low-voltage supply is stable and correctly rated for the thermostat.
If E5 persists with a known-good power source, the thermostat internal regulator may be defective and the unit should be replaced.
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Repair Difficulty
Medium
3/5
Required Part
Saunier Duval Smart Thermostat Power Adapter
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