The Honeywell Aquastat Relay is an immersion controller that comes in both vertical and horizontal mounting models. The unit has high-low control and a manual switch, and it also provides heat-conducive compound. Most units include accessory and transformer terminals, allowing for the addition of a low-limit controller, and cases are available for both the vertical and horizontal models.
The relay comes with a high-limit switch to shut off the burner when temperatures surpass the high-limit setting. This setting should be the temperature recommended by the boiler manufacturer. Users set the high-limit temperature upon completion of unit installation.
The room thermostat controls the switching relay. When heating is needed, the coil becomes energized, which then completes the line voltage and burner circuits when the temperature of the boiler water is under the high-limit temperature.
The relay also comes with an auto/manual switch that allows the burner to operate during a failure of electrical power. When the switch is set to manual, the burner works until the high-limit temperature is exceeded or until the user resets the switch to auto. Once electrical power has been restored, the user must reset the switch to auto so that the system can return to automatic burner function.