Yellow | On every 0.5 second Low

Vokera Yellow | On every 0.5 second Fault Code

Also written as YELLOWONEVERY05SECOND — same fault.

The Vokera Yellow | On every 0.5 second fault code means: your boiler is currently in a manual testing mode often used by engineers and is not experiencing a functional fault.. It appears on 1 Vokera model 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: Service function

What causes the Vokera Yellow | On every 0.5 second fault?

This status occurs because the boiler has been manually put into 'Service Mode' using the internal control selectors. It is physically triggered when the mode selector dial is turned to the specific testing position, usually to allow an engineer to measure gas pressures without the boiler modulating. It is not a component failure, but rather a sign that a manual override is currently active.

Typical repair cost £0-80 (including labour)

DIY fix possible

Check if the mode selector dial has been left in the 'Service' or 'Chimney' position.Turn the selector dial to the 'OFF' position for 30 seconds.Turn the selector dial back to your desired 'Hot Water' or 'Heating' setting to resume normal operation.

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Vokera models that show the Yellow | On every 0.5 second fault code

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

Source

Vokera Yellow | On every 0.5 second fault code information on this page is sourced and cross-checked against the official Vokera service / installation manuals for each affected model.

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