BoilerFaultCodesIdeal 4.3 Fault Code
Also written as 43 — same fault.
The Ideal 4.3 fault code means: your boiler has failed to light after several attempts, meaning it has shut down as a safety precaution and will not provide heating or hot water.. It appears on 5 Ideal models in our database.
Technical description: Ignition Lockout
What causes the Ideal 4.3 fault?
This fault occurs when the boiler tries to light itself several times but fails to detect a stable flame. The most common reasons are a lack of gas supply to the unit, a dirty ignition component that can no longer create a spark, or a debris-clogged burner.
This issue often surfaces during the first cold snap of winter when components that have been idle over summer are suddenly put under increased strain.
DIY fix possible
Check if other gas appliances in your home, such as a gas hob, are working to ensure gas is reaching the property.Ensure your pre-payment gas meter has credit if applicable.Press the 'Reset' button on the boiler control panel once to see if it restarts. Only attempt this three times maximum.If it is freezing outside, check that your white plastic condensate pipe leading outdoors is not frozen and blocked.
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Gas Safe Register →Ideal models that show the 4.3 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 4.3 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