How much does it cost to fix Ideal error code 78?

Typical repair cost for the Ideal 78 fault is £150-250 including labour.

78 High

Ideal 78 Fault Code

Q: What does the Ideal 78 fault code mean?

Your boiler has detected a communication issue with the sensor that monitors the temperature of the exhaust fumes, causing it to shut down for safety reasons.

The Ideal 78 fault code means: your boiler has detected a communication issue with the sensor that monitors the temperature of the exhaust fumes, causing it to shut down for safety reasons.. It appears on 1 Ideal model in our database.

Technical description: FLUE THERMISTOR ERROR

Typical repair cost £150-250 (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 78 fault code

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

Mexico HE Repair: £150-250

Source

Ideal 78 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