40
FAULT CODE
Viessmann
Internal Bus Communication Fault
High Severity
Engineer Required
There is a communication fault on the internal data bus between boiler components. The PCB may have a fault.
Step-by-Step Fix Guide
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Step 1
Try power cycling the boiler — switch off at the spur for 60 seconds
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Step 2
If the fault persists, the PCB or wiring harness may need attention
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Step 3 Engineer only
A Gas Safe engineer will need to diagnose the fault
Gas Safe Reminder
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.