Viessmann · Vitodens 100-W combi
91 boiler fault code
Vitodens 100-W type B1KF combi
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What 91 means
DIO electronics module communication error; function of affected extension in emergency (fallback) mode
Safe check
Note the code shown on the display. Do not open or adjust the boiler, or repeatedly reset it. Contact a Gas Safe registered engineer.
When to contact an engineer
Contact a Gas Safe registered engineer for diagnosis of this fault code.
Safety notice
A boiler fault code alone is not a gas or carbon-monoxide emergency. If you smell gas, a CO alarm sounds, anyone feels unwell, or there is an unsafe flame, leave and call 0800 111 999 from outside.
Source and provenance
- Viessmann Vitodens 100-W types B1HF/B1KF · chapter 7 “Troubleshooting”, “Fault messages” · code 91, printed p. 72; emergency function/mode means appliance fallback operation, not emergency routing
installation and service instructions for contractors
6167586 GB · 3/2023