Viessmann Flow Switch (Page 2)

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 DHW and central heating systems. When the pump is activated, the flow switches senses this movement and feeds the information back to the PCB, allowing the ignition sequence to progress. The flow switches purpose is to make sure that the burner cannot switch on whilst the system is dry or low on water.