d.90 Low

Vaillant d.90 Fault Code

Also written as D90 — same fault.

The Vaillant d.90 fault code means: your boiler is having a minor communication issue with your thermostat, which means it may not be receiving correct instructions on when to turn the heating on or off.. It appears on 10 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: Status of the eBUS room thermostat
Typical repair cost £80-150 (including labour)

DIY fix possible

Check that your room thermostat has fresh batteries and the screen is activeEnsure the thermostat is not showing a 'no connection' or 'signal lost' iconTurn the boiler off at the mains switch for 60 seconds and turn it back on to reset the connection

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Vaillant models that show the d.90 fault code

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

Source

Vaillant d.90 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 31 August 2026