BoilerFaultCodesIdeal I3 Fault Code
The Ideal I3 fault code means: your boiler is not receiving any electrical power, which is why the lights are off and it isn't working.. It appears on 1 Ideal model in our database.
Technical description: Mains On neon - if not illuminated check mains supply, fuses, and input wiring
What causes the Ideal I3 fault?
This fault occurs when the boiler's control system detects a complete break in the electrical circuit required to run the unit. The most common reason is a blown fuse or a loose connection in the wiring, which prevents electricity from reaching the internal components. In some cases, a surge may have damaged the main circuit board, causing it to fail entirely.
DIY fix possible
Check if your home's main consumer unit (fuse box) has tripped.Ensure the boiler's isolation switch (usually a white switch near the boiler) is turned on.Check the fuse in the boiler's fused spur switch, replacing it with a 3-amp fuse if necessary.
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Gas Safe Register →Ideal models that show the I3 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal I3 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