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