BoilerFaultCodesIdeal DHW Thermistor Fault Fault Code
Also written as DHWTHERMISTORFAULT — same fault.
The Ideal DHW Thermistor Fault fault code means: your boiler is struggling to accurately measure the temperature of your hot water, which typically means your taps will only run cold or have inconsistent heat.. It appears on 3 Ideal models in our database.
Technical description: Insecure electrical connection, incorrect resistance values (9.7-10.3 kΩ at 25°C), or lack of continuity between the PCB and the thermistor.
What causes the Ideal DHW Thermistor Fault fault?
This fault occurs when the internal sensor responsible for monitoring hot water temperature starts sending incorrect signals to the main control board. The most common reason is that the sensor's internal components have degraded over time or a wire has shaken loose, leaving the boiler unable to tell how hot the water actually is. As a safety precaution, the boiler will stop heating the water to prevent it from reaching dangerous temperatures.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Ideal models that show the DHW Thermistor Fault fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal DHW Thermistor Fault 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