The Glow-worm flow switch acts as a safety device. It is a switch with an in-built sensor that sits in the pipework for both the domestic hot water and central heating systems. When the pump is powered up, the flow switches sense this movement and feed the information back to the printed circuit board, allowing the ignition sequence to progress. The flow switch's purpose is to make sure that the burner cannot switch on if the system is dry or low on water.

• Compatible with the Glow-worm Ultracom