E8
Danfoss Ally
Power Supply / Voltage Error
E8 error and thermostat frequently restarts or becomes unresponsive when calling for heat.
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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
Incorrect supply voltage to wall thermostat, Loose terminal connections, Faulty internal power supply circuit, Overvoltage from boiler control wiring
How to Fix / Troubleshooting
Safety first: Isolate power at the main breaker and verify that all circuits are dead before touching wiring.
Steps:
- Verify supply voltage: Using a multimeter, measure the voltage at the thermostat supply terminals. Confirm it matches the rating in the Danfoss Ally manual (e.g. 230 V AC for mains models).
- Tighten terminals: Check that all screw terminals are tight and that no copper strands are exposed or touching adjacent terminals.
- Check boiler interface: If the thermostat is connected to a boiler control bus or external relay, ensure that only the specified type of connection (e.g. dry contact) is used. Incorrectly feeding mains into a low‑voltage input can damage the thermostat.
- Inspect for damage: Look for burn marks or a burnt smell from the thermostat. If present, do not reuse it; replace immediately.
- Replace if needed: If E8 persists with correct voltage and wiring, the internal power supply is likely damaged. Replace the thermostat.
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Repair Difficulty
Hard
4/5
Required Part
Danfoss Ally Room Thermostat (internal power supply)
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