Your boiler is temporarily pausing because it has noticed an unusual temperature difference between two internal sensors and is performing a self-check to ensure everything is working correctly.

Flow-/Return-sensor check is running, demand (DHW or heating) is blocked

What causes this fault?

This status occurs when the boiler's internal computer notices that the temperatures on the flow and return pipes are not changing in the way it expects. To prevent damage, the boiler pauses operation to double-check that the sensors are reporting accurately and that water is actually moving through the heat exchanger. This is often caused by a failing pump or a buildup of debris that is slowing down the flow of water.