D2
Nibe
Overtemperature in heating circuit
D2 alarm, flow temperature too high, safety thermostat may trip
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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
Closed radiator valves, failed circulation pump, stuck 3‑way valve, incorrect control settings causing too high flow temperature
How to Fix / Troubleshooting
Safety: Risk of scalding from hot water. Allow system to cool before bleeding or opening components.
- Open valves: Ensure that enough radiators or underfloor loops are open to dissipate heat. Do not run the furnace against a closed system.
- Check circulation pump: Confirm that the heating pump is running and not air‑locked (see B1 guidance).
- Inspect 3‑way valve: If your Nibe unit uses a 3‑way valve to switch between heating and hot water, verify that it moves correctly and is not stuck in one position.
- Review settings: In the Nibe menu, check the maximum flow temperature setting and adjust to recommended values for your system.
After corrections, reset the D2 alarm. If overheating continues, a technician should check sensors and safety thermostats.
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Repair Difficulty
Medium
3/5
Required Part
Safety Thermostat
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