BoilerFaultCodesIdeal Return Thermistor Fault Fault Code
Also written as RETURNTHERMISTORFAULT — same fault.
The Ideal Return Thermistor Fault fault code means: your boiler has detected an issue with a temperature sensor that monitors the water returning from your radiators, preventing the system from heating up safely.. It appears on 7 Ideal models in our database.
Technical description: Wiring or resistance issues with the Return Thermistor located in the pump housing (upper LHS of boiler).
What causes the Ideal Return Thermistor Fault fault?
This fault occurs when the boiler's control board receives an incorrect or missing signal from the sensor that measures the temperature of the water coming back from your radiators. The most common reason is that the internal sensor has developed a physical defect or the electrical connection has become loose or corroded over time.
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 Return Thermistor Fault fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal Return Thermistor Fault fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.
- Ideal Atlantic Combi manual (PDF)
- Ideal Logic Max Heat 2 manual (PDF)
- Ideal Logic Max System 2 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026