Your boiler is temporarily pausing to check its temperature sensors before heating your home, which may cause a delay in getting hot water or heating.

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

What causes this fault?

This fault occurs when the boiler detects an unusual difference in readings between its two temperature sensors, prompting it to pulse the pump and compare the figures. The most common reason is that the sensors have become uncalibrated or the water isn't moving through the heat exchanger quickly enough for the boiler to trust the data. If the readings don't align during this check, the boiler will temporarily prevent itself from firing to avoid overheating.