BoilerFaultCodesViessmann F.981 Fault Code
Also written as F981 — same fault.
The Viessmann F.981 fault code means: your boiler has stopped producing hot water because the internal water pressure in your heating system has dropped too low to operate safely.. It appears on 1 Viessmann model in our database.
Technical description: No DHW heating. Minimum system pressure is too low during DHW heating.
DIY fix possible
Locate the external filling loop, usually two silver valves connected by a flexible metal hose under the boiler.Open the valves slowly to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves tightly and restart the boiler to clear the fault.
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Viessmann models that show the F.981 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann F.981 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 7 July 2026