H9/L9 Emergency

Ideal H9/L9 Fault Code

Also written as H9L9 — same fault.

The Ideal H9/L9 fault code means: your boiler has detected that the gases venting out of your home are getting too hot, so it has safely shut itself down to prevent damage or safety issues.. It appears on 7 Ideal models in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: FLUE GAS OVERHEAT
Typical repair cost £150-350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Ideal models that show the H9/L9 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Ideal H9/L9 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