BoilerFaultCodesIdeal LED1 flashing, LED2 on Fault Code
Also written as LED1FLASHINGLED2ON — same fault.
The Ideal LED1 flashing, LED2 on fault code means: your boiler has detected a problem with the sensor that monitors the temperature of your central heating water, meaning it can't heat your radiators safely.. It appears on 6 Ideal models in our database.
Technical description: Faulty CH thermistor or wiring
What causes the Ideal LED1 flashing, LED2 on fault?
This fault occurs when the internal sensor responsible for tracking the temperature of your radiators fails to send a reliable signal to the boiler's control board. The most common reason is that the sensor has physically degraded over time or the electrical connection has become loose, preventing the boiler from knowing when to safely turn the burner on or off.
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 LED1 flashing, LED2 on fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal LED1 flashing, LED2 on 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