BoilerFaultCodesVaillant d.2 Fault Code
Also written as D2 — same fault.
The Vaillant d.2 fault code means: your boiler is currently taking a temporary break from heating after successfully reaching its target temperature to prevent it from turning on and off too frequently.. It appears on 13 Vaillant models in our database.
Technical description: Maximum burner anti cycling period at 20 °C flow temperature
What causes the Vaillant d.2 fault?
This status occurs when your boiler has reached its required temperature and needs to wait for the water in your radiators to cool down before firing up again. It is a built-in protection feature designed to stop the burner from turning on and off too rapidly, which saves energy and protects the internal components from unnecessary wear. Once this brief 'anti-cycling' timer finishes, the boiler will automatically resume heating your home.
This is more common during autumn and spring when the weather is milder and your home requires less intensive heat to stay warm.
DIY fix possible
Check if the room thermostat is set to your desired temperatureWait up to 20 minutes for the countdown timer to finishEnsure your radiator valves are turned to the 'on' position
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Vaillant models that show the d.2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant d.2 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoMAX manual (PDF)
- Vaillant ecoMAX System 612 manual (PDF)
- Vaillant ecoMAX 824E manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026