BoilerFaultCodesViessmann 98:1 to 98:5 Fault Code
Also written as 981TO985 — same fault.
The Viessmann 98:1 to 98:5 fault code means: your boiler has detected an internal configuration error or a communication fault with its electronic control system.. It appears on 5 Viessmann models in our database.
Technical description: System number adjustable from 1 to 5
What causes the Viessmann 98:1 to 98:5 fault?
This fault occurs when the boiler's internal memory loses track of the specific heating layout it is supposed to manage, such as whether it is heating just radiators or a hot water cylinder too. The most common reason is a communication error between the main control board and the coding plug, which acts like a small identity chip for the appliance. Without this clear 'identity,' the boiler stops operating because it no longer knows which internal components to activate.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Viessmann models that show the 98:1 to 98:5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 98:1 to 98:5 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 27 April 2026