BoilerFaultCodesUnical 43 Fault Code
The Unical 43 fault code means: your boiler is failing to keep a stable flame lit during startup, which causes it to safely shut down to prevent gas from building up.. It appears on 2 Unical models in our database.
Technical description: During the ignition stage, abnormal flame extinguishing has occurred 12 "consecutive" times in a period of about 50 / sec. Check the gas pressure / any flue gas recirculation in the chimney and obstructions / condensation drain / electrode electrical connection / electrode and burner earth / perform GAC calibration chap. 4.3.1 / replace the electrode and its connection / replace the electronic board
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Unical models that show the 43 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Unical 43 fault code information on this page is sourced and cross-checked against the official Unical service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026