BoilerFaultCodesYour boiler is temporarily pausing to double-check that its internal temperature sensors are reading correctly before it starts heating your home.
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: Flow/return sensor test running, heating demands are blocked
What causes this fault?
This occurs when the boiler detects a suspicious difference between the temperature readings on the flow and return pipes. It marks a temporary pause while the system performs a self-test to ensure the sensors haven't drifted out of calibration or failed. Usually, this is caused by poor water circulation or a sensor that is beginning to fail and sending inaccurate data to the main control board.
This status is more frequent in autumn when heating systems are first turned back on, as stagnant pump components or air pockets can hinder the water flow required for a successful sensor test.
DIY fix possible
Wait for up to 15 minutes as this is often a self-diagnostic checkEnsure all radiator valves are open to allow water to circulateReset the boiler if the code persists for more than 30 minutes
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