The frost protection sensor should be installed inside your boats cabin space and when the internal temperature drops below 3°C it will automatically start the heater unit and raise the temperature to approximately 7°C, when it will switch the unit off. This bypasses any timer control that may be fitted to the system and allows you to leave the boat during the winter period without worrying about the cold weather.
The unit would benefit from being fitted low down in the cabin area as any rise in temperature due to sunlight etc. could falsely affect the temperature reading for the thermostat.
Please Note: This unit will start the Webasto heater as necessary depending on the internal air temperature of the boat. Please make sure that your batteries and fuel levels are at a sufficient level to ensure the Webasto can function correctly.