This part is located around the flow switch section. The flow switch acts as a safety mechanism. It is a switch with an in-built sensor that sits in the pipework for both the central heating and DHW systems. When the pump is activated, the flow switches senses this movement and feeds the information back to the printed circuit board, allowing the ignition sequence to progress. The flow switches purpose is to make sure that the burner cannot switch on whilst the system is low on water or dry.
We recommend that all parts are fitted by a fully qualified gas safe certified plumber.