BoilerFaultCodesIdeal 81 Fault Code
The Ideal 81 fault code means: your boiler has stopped working because a sensor that measures the internal water temperature is not sending a proper signal, leaving the system unsure how much heat it should produce.. It appears on 6 Ideal models in our database.
Technical description: FLOW THERMISTOR FAULT
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.
- Ideal Icos System manual (PDF)
- Ideal Logic Air manual (PDF)
- Ideal Logic Code Combi ESP1 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026