BoilerFaultCodesYour boiler is temporarily pausing to test a temperature sensor before it starts up, which is delaying your heating or hot water.
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 because the boiler's control board needs to verify that the temperature sensors are reading correctly before it allows the burner to light. It happens when the system detects an unusual temperature difference between the pipes, forcing a brief pause to ensure the sensors haven't failed. The most common reason is a drifting or faulty return thermistor that is providing inaccurate data to the boiler.
DIY fix possible
Wait for up to 15 minutes as this is often a self-correcting diagnostic checkSwitch the boiler off at the fused spur switch, wait 30 seconds, and switch it back onCheck that all radiator valves are open to ensure water can circulate freely
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