BoilerFaultCodesIdeal 405 Fault Code
The Ideal 405 fault code means: your boiler’s internal computer has encountered a critical electronic error and can no longer control the heating system safely.. It appears on 2 Ideal models in our database.
Technical description: internal failure - electronic
What causes the Ideal 405 fault?
This fault occurs when the boiler's main control board suffers a hardware failure, meaning the electronic components can no longer communicate with each other. The most common reason is age-related wear to the circuitry or an electrical surge that has damaged the delicate microprocessors inside the unit.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Ideal models that show the 405 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 405 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