BoilerFaultCodesKeston Return Thmr Fault Fault Code
Also written as RETURNTHMRFAULT — same fault.
The Keston Return Thmr Fault fault code means: your boiler's temperature sensor at the water return pipe is faulty or disconnected, causing the system to stop heating because it cannot accurately measure the water temperature.. It appears on 2 Keston models in our database.
Technical description: Check Return Thermistor Wiring, Check Return Thmr
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Keston models that show the Return Thmr Fault fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston Return Thmr Fault fault code information on this page is sourced and cross-checked against the official Keston service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026