Viessmann · Vitodens 100-W combi
78 boiler fault code
Vitodens 100-W type B1KF combi
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What 78 means
No communication between heat management unit and programming unit
Safe check
Note the code shown on the display. Do not open, adjust or repeatedly reset the boiler. Contact a Gas Safe registered engineer.
When to contact an engineer
The code remains or returns after the step above, or no home step applies; arrange diagnosis by a Gas Safe registered engineer.
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” Cause column · code 78, p. 72
installation and service instructions for contractors
6167586 GB · 3/2023