N.027 Medium

Vaillant N.027 Fault Code

Also written as N027 — same fault.

The Vaillant N.027 fault code means: your boiler is struggling to accurately measure the temperature of the water used for your taps and shower, which will likely result in the water being cold or failing to heat up at all.. It appears on 3 Vaillant models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Temperature sensor defective. The signal for the temperature sensor on the domestic hot water connection is implausible.
Typical repair cost £120-220 (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 N.027 fault code

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

Source

Vaillant N.027 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 7 July 2026