BoilerFaultCodesUnical 18 Fault Code
The Unical 18 fault code means: your boiler has detected moisture or a positioning issue around the internal ignition sensor, which prevents it from safely lighting the flame.. It appears on 2 Unical models in our database.
Technical description: Electrode earthed on the Burner or presence of moisture. Check the distance between the burner and the electrode, check for humidity between drain wire and ceramic, if necessary, replace the electrode.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like 18: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Unical models that show the 18 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Unical 18 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