BoilerFaultCodesVokera 21 Fault Code
The Vokera 21 fault code means: your boiler has detected a loose or faulty electrical connection inside its control system, which is preventing it from communicating with its internal components correctly.. It appears on 4 Vokera models in our database.
Technical description: check the wiring harness
What causes the Vokera 21 fault?
This fault occurs when the boiler's main control board loses the electronic signal from the external timer or room thermostat, causing a break in communication. It can also happen if the boiler becomes stuck in an internal calibration mode after a power cut or a system reset. Essentially, the 'brain' of the boiler is waiting for a command to start that it can no longer hear.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vokera models that show the 21 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vokera 21 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 7 July 2026