81 Medium

Ideal 81 Fault Code

The Ideal 81 fault code means: your boiler is temporarily locked out because it is receiving an incorrect temperature reading from the pipe returning water back into the system.. It appears on 7 Ideal models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: RETURN THERMISTOR FAULT
Typical repair cost £120-£220 (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 81 fault code

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

Source

Ideal 81 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 31 August 2026