BoilerFaultCodesIdeal Mains On neon NOT lit Fault Code
Also written as MAINSONNEONNOTLIT — same fault.
The Ideal Mains On neon NOT lit fault code means: your boiler has no power and is completely unresponsive, likely due to an electrical supply issue or a blown fuse.. It appears on 2 Ideal models in our database.
Technical description: Check connections and continuity of EMC filter or rectify external fault.
What causes the Ideal Mains On neon NOT lit fault?
This fault occurs when electrical power fails to reach the boiler's internal controls, leaving the unit completely lifeless. The most common reason is a blown fuse in the external wall switch or a surge that has tripped the boiler's internal protection, often caused by a failing component like the pump or fan. In some cases, the interference filter has failed, preventing electricity from flowing through the circuit safely.
DIY fix possible
Check if your home's main electrical consumer unit has a tripped circuit breakerEnsure the boiler's external isolation switch (fused spur) is turned onReplace the 3-amp fuse in the external isolation switch with a new one
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Ideal models that show the Mains On neon NOT lit fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal Mains On neon NOT lit 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 7 July 2026