The Vaillant brass aqua sensor acts as a safety device. 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 turned on, the flow switches sense this movement and feed the information back to the electronic control, allowing the ignition sequence to progress. The function of the flow switch is to make sure that the burner cannot switch on whilst the system is low on water or dry.

Brand Name	Vaillant