How much does it cost to fix Ideal error code L05?

Typical repair cost for the Ideal L05 fault is £90-£160 including labour.

L05 High

Ideal L05 Fault Code

Q: What does the Ideal L05 fault code mean?

Your boiler has lost its ability to accurately measure the temperature of the water coming back into the system, which is preventing it from heating up correctly.

The Ideal L05 fault code means: your boiler has lost its ability to accurately measure the temperature of the water coming back into the system, which is preventing it from heating up correctly.. It appears on 3 Ideal models in our database.

Technical description: Return Thermistor Fault

What causes the Ideal L05 fault?

This fault occurs when the sensor responsible for monitoring the temperature of the water returning to the boiler fails or provides an illogical reading. The most common reason is that the internal component has suffered an electrical failure or the wiring connecting it to the main control board has become loose or damaged.

Typical repair cost £90-£160 (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 L05 fault code

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

Source

Ideal L05 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