BoilerFaultCodesIdeal LED1 on, LED2 flashing Fault Code
Also written as LED1ONLED2FLASHING — same fault.
The Ideal LED1 on, LED2 flashing fault code means: your boiler has detected a problem with how it moves air and exhaust gases through the system, preventing it from firing up safely.. It appears on 6 Ideal models in our database.
Technical description: Air pressure switch fault (fan running, but switch not operating or flue/venturi blocked)
What causes the Ideal LED1 on, LED2 flashing fault?
This fault occurs when the boiler's internal safety sensor cannot confirm that the fan is successfully pushing exhaust gases out of the flue. The most common reasons are a build-up of debris in the small plastic tubes inside the unit or a mechanical failure in the fan or air pressure sensor. Without this confirmation, the boiler refuses to light the gas burner to prevent dangerous fumes from backing up into your home.
This issue is more frequent during periods of heavy wind or storms, as high gusts can sometimes interfere with the pressure balance in the flue system.
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 on, LED2 flashing fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal LED1 on, LED2 flashing 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