How much does it cost to fix Ideal error code 4.9?

Typical repair cost for the Ideal 4.9 fault is £100-180 including labour.

4.9 High

Ideal 4.9 Fault Code

Q: What does the Ideal 4.9 fault code mean?

Your boiler has detected an issue with a temperature sensor that monitors the water returning from your radiators, often resulting in the system shutting down for safety.

Also written as 49 — same fault.

The Ideal 4.9 fault code means: your boiler has detected an issue with a temperature sensor that monitors the water returning from your radiators, often resulting in the system shutting down for safety.. It appears on 8 Ideal models in our database.

Technical description: Return Thermistor Fault

What causes the Ideal 4.9 fault?

This fault occurs when the boiler's control board loses communication with the sensor that monitors the temperature of the water coming back from your radiators. The most common reason is that the sensor itself has developed an internal electrical failure or the wiring connecting it to the main computer has become loose or damaged. Because the boiler can no longer safely track how much heat is being removed from the system, it shuts down to prevent overheating.

Typical repair cost £100-180 (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 4.9 fault code

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

Source

Ideal 4.9 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