BoilerFaultCodesIdeal 1C Fault Code
The Ideal 1C fault code means: your boiler has detected that a safety sensor meant to monitor exhaust gases is disconnected or has failed, causing the system to shut down for protection.. It appears on 1 Ideal model in our database.
Technical description: Connection for flue gas thermostat not closed.
What causes the Ideal 1C fault?
This fault occurs when the boiler's control system loses its electrical connection to the sensor that monitors the temperature of the exhaust gases. The most common reason is a vibration-loosened wiring connector or a physical failure of the thermostat itself, which serves as a vital safety barrier to prevent the unit from overheating. Because the boiler can no longer verify that exhaust temperatures are safe, it will shut down immediately to prevent damage.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Ideal models that show the 1C fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 1C 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