The flow switch acts as a safety device. It is a switch with an in-built sensor that sits in the pipework for both the heating and domestic hot water systems. When the pump is switched on, the flow switches senses this movement and feeds the information back to the printed circuit board, allowing the ignition sequence to progress. The function of the flow switch is to make sure that the burner cannot switch on if the system is low on water or dry.
We recommend that all parts are fitted by a fully qualified gas safe certified plumber.