9.1.8 High

Ideal 9.1.8 Fault Code

Also written as 918 — same fault.

The Ideal 9.1.8 fault code means: your outdoor heat pump unit has detected a fault with a temperature sensor that monitors the air passing through it, which may cause the system to stop working correctly.. It appears on 1 Ideal model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Outdoor Unit, Air to Refrigerant Heat Exchanger Outlet Thermistor (T3) Error

What causes the Ideal 9.1.8 fault?

This fault occurs when the heat pump's control system loses the ability to accurately read the temperature of the air as it leaves the outdoor unit. The most common reason is that the sensor has developed an internal electrical failure or the wiring connecting it to the main control board has become loose or damaged.

This fault can be more frequent during periods of heavy frost or high humidity, as ice build-up on the outdoor unit can sometimes physically stress the sensor or its wiring.

Typical repair cost £160-£320 (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 9.1.8 fault code

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

Source

Ideal 9.1.8 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