BoilerFaultCodesIdeal 18 Fault Code
The Ideal 18 fault code means: your boiler is struggling to breathe properly because there is a blockage or too much debris in the air intake or exhaust system.. It appears on 2 Ideal models in our database.
Technical description: Too much resistance or dirt in the air circuit; check the air supply/combustion gas discharge system, the burner, and the heat exchanger.
What causes the Ideal 18 fault?
This fault occurs when the boiler's internal sensors detect that air cannot flow freely through the system to support safe combustion. The most common reason is a buildup of debris or soot within the heat exchanger or burner, which physically restricts the path of the gases. It can also be caused by an external blockage in the flue pipe or a failing fan that is unable to push air through the circuit effectively.
This fault often appears during the first heavy use of autumn or winter, as dust or debris settled during the summer months can be pulled into the burner when the heating starts running at full power.
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 →Ideal models that show the 18 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 18 fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026