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 CH and domestic hot water systems. When the pump is powered up, 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 function 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 technician.