D.98 Low

Vaillant D.98 Fault Code

Also written as D98 — same fault.

The Vaillant D.98 fault code means: this is a prompt or status message indicating that the boiler requires professional maintenance or has reached a specific service interval that needs an engineer's attention.. It appears on 4 Vaillant models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Telephone a heating engineer

What causes the Vaillant D.98 fault?

This message is triggered by an internal timer or a specific number of burner operating hours set by a previous engineer. It physically indicates that the boiler has reached its scheduled maintenance interval and requires a safety inspection rather than being a sign of a mechanical breakdown. The status is designed to ensure the appliance continues to run efficiently and safely through preemptive servicing.

Typical repair cost £80-160 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the D.98 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant D.98 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026