BoilerFaultCodesViessmann 74 Fault Code
The Viessmann 74 fault code means: your boiler has stopped working because the water pressure in the system has dropped too low to operate safely.. It appears on 1 Viessmann model in our database.
Technical description: System pressure too low; burner locked out
DIY fix possible
Locate the filling loop (usually a silver braided hose with one or two small valves) underneath the boiler.Slowly open the valve(s) until you hear water entering the system and watch the pressure gauge.Close the valves tightly once the pressure reaches between 1.0 and 1.5 bar, then reset the boiler.
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Viessmann models that show the 74 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 74 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