Your boiler has detected that water is failing to circulate correctly through the system, which will prevent it from heating your home or providing hot water.

The diagnostics will indicate the nature of the fault to assist a speedy and effective repair

What causes this fault?

This fault occurs when the boiler's internal sensors detect that water is not moving through the heat exchanger at the required rate, often due to a mechanical failure or a blockage. The most common reason is a seized or worn-out circulation pump, though it can also be caused by air trapped in the system or a build-up of sludge obstructing the flow. Without this movement, the boiler must shut down to prevent the unit from overheating and causing internal damage.