BoilerFaultCodesYour boiler is briefly pausing to check its temperature sensors before it starts up, which is a normal self-test process.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: Return-Sensor check is running, demand (DHW or heating) is blocked
What causes this fault?
This occurs when the boiler performs a safety check to ensure the temperature sensors are reading accurately before firing up. It physically pauses operation because it has detected a slight discrepancy or is waiting for the return sensor to confirm the system state is safe to proceed. In most cases, this is a momentary software calculation rather than a mechanical failure.
DIY fix possible
Wait for a few minutes to see if the code clears automaticallyEnsure your radiator valves are open to allow water to circulateCheck if the boiler pressure is between 1.0 and 1.5 bar
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