BoilerFaultCodesIdeal H1 Fault Code
The Ideal H1 fault code means: your boiler has stopped working because it cannot properly measure the temperature of the water leaving the unit.. It appears on 5 Ideal models in our database.
Technical description: FLOW THERMISTOR ERROR
What causes the Ideal H1 fault?
This fault occurs when the boiler's control board loses communication with the sensor that monitors the temperature of the water being sent to your radiators. The most common reason is that the sensor has electronically failed or 'drifted' out of its correct range, making it impossible for the boiler to operate safely. In some cases, it can also be caused by loose or damaged internal wiring connecting the sensor to the main computer.
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 H1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal H1 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