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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing). Published: February 7, 2024. Updated: May 17, 2024

Vaillant F27 Fault Code – How to fix

Vaillant boilers use error codes to signal issues. An F27 fault indicates an incorrect flame due to gas-flame imbalance.

Repair costs will vary. Potential solutions range from component repairs to a complete boiler replacement. It is essential to diagnose the issue correctly.

Boiler malfunctions can be alarming, and understanding their signals is crucial. Vaillant use error codes to communicate specific problems to homeowners.

What Does F27 Mean?

An F27 error code on Vaillant ecoTEC Pro and Plus boilers indicates an incorrect flame. This is due to an imbalance between gas and flame. This can lead to either an overactive or underperforming boiler. This error prompts a system lockout, disabling heating and hot water to prevent further damage.

Common Causes of F27 Errors

The root causes of an F27 fault vary. They include moisture on electrical components, gas valve errors, failed ignition leads or spark electrodes and PCB failure. Less commonly, flame sensor faults. Each of these issues suggests a different repair approach, necessitating professional evaluation.

Professional Intervention

Addressing an F27 error is not a DIY task. It requires a Gas Safe registered engineer to ensure safety and compliance with legal requirements. From diagnosis to repair, the involvement of a professional is non-negotiable.

Cost Implications

Repair costs for an F27 error can range from cleaning electrical components to replacing the PCB or even having to install a new boiler. It will depend on the severity of the fault and the boiler’s age.

Prices vary based on location, the nature of the fault, and the extent of damage.

Warranty Coverage

Vaillant’s warranty may cover repairs or replacements if the fault is due to a manufacturing defect. However, warranty validity is contingent on the specific terms and conditions at the time of installation.


In summary, an F27 fault code on a Vaillant boiler signals a serious issue requiring professional attention. Homeowners should not attempt DIY repairs but instead seek the expertise of a Gas Safe registered engineer. An emergency boiler replacement may be required.

Unfortunately, your boiler may be unrepairable. If this is the case, get a boiler replacement quote for a premium boiler with Boilerhut:

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