BoilerFaultCodesIdeal 403 Fault Code
The Ideal 403 fault code means: your boiler’s internal computer has encountered a critical electronic error and can no longer communicate with the main system.. It appears on 2 Ideal models in our database.
Technical description: internal failure - electronic
What causes the Ideal 403 fault?
This fault occurs when the boiler’s central brain suffers a critical hardware failure, preventing it from processing information or sending commands to other components. It is often caused by an electrical surge, moisture ingress onto the circuitry, or general component degradation over time. Because the internal communication has broken down, the system shuts down entirely to ensure safety.
This fault is slightly more common during winter or storm season, as increased electrical grid activity and power surges can damage sensitive electronic components.
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 403 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 403 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