T8 High

Ideal T8 Fault Code

The Ideal T8 fault code means: your boiler is struggling to switch to its high-power mode because of an electrical signaling issue within its internal control system.. 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: Stage 2 "boiler on" thermostat output / Insert in the control circuit of burner stage 2
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 T8 fault code

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

Source

Ideal T8 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