BoilerFaultCodesViessmann 60:5 to 60:25 Fault Code
Also written as 605TO6025 — same fault.
The Viessmann 60:5 to 60:25 fault code means: your boiler is struggling to reach the temperature requested for your hot water because the internal settings are set too high or a sensor is misreading.. It appears on 5 Viessmann models in our database.
Technical description: The difference between the boiler water temperature and the set DHW temperature is adjustable from 10 to 50K
What causes the Viessmann 60:5 to 60:25 fault?
This fault happens when the boiler cannot maintain the correct temperature gap between the hot water being heated and the burner's settings. It is often caused by a buildup of limescale or debris inside the plate heat exchanger, which prevents heat from transferring efficiently into your taps. Alternatively, a faulty sensor inside the unit might be providing inaccurate readings, causing the system to struggle with temperature regulation.
This issue is often more noticeable in winter when the incoming mains water is much colder, forcing the boiler to work harder to reach the target temperature.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Viessmann models that show the 60:5 to 60:25 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 60:5 to 60:25 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026