BoilerFaultCodesBiasi 18 + Fault Code
Also written as 18 — same fault.
The Biasi 18 + fault code means: your boiler has stopped because it cannot detect a temperature difference when trying to heat up, which usually means water isn't moving through the system properly.. It appears on 4 Biasi models in our database.
Technical description: No ∆T heating at start-up.
DIY fix possible
Check that all radiator valves are fully openEnsure the system pressure is between 1.0 and 1.5 bar on the gaugeBleed all radiators to remove trapped airReset the boiler using the control knob
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Gas Safe Register →Biasi models that show the 18 + fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Biasi 18 + fault code information on this page is sourced and cross-checked against the official Biasi service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026