BoilerFaultCodesUnical 15 Fault Code
The Unical 15 fault code means: your boiler is overheating because water isn't flowing through the system quickly enough to take the heat away.. It appears on 2 Unical models in our database.
Technical description: wATER CIRCULATION INSUFFICIENT Primary circuit water circulation insufficient (∆t > 35° C)
DIY fix possible
Check that your boiler pressure gauge is between 1.0 and 1.5 barEnsure all radiator valves and the boiler isolation valves are fully openBleed your radiators to remove any trapped air pockets
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Unical models that show the 15 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Unical 15 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 7 July 2026