The sensor on the D-D ATO has different light colours and patterns to warn of faults or show its status.

A red light on the sensor can indicate three things.

• The sensor has an inbuilt emergency shut off timer. When the unit performs its first top up after being powered on it will store the time taken in its memory. If for any reason the top up unit is activated for longer than 6 times this the sensor will assume there is a problem or that the freshwater reservoir is empty, shut down and show the red warning light. If this has occurred check that the sensor is clean, the impellor in the pump is clean and free to move, the freshwater reservoir is not empty and that there is nothing that could be causing the sump water level to fall unexpectedly.
• To set the ATO back into normal operation mode and clear the alarm status, power the unit down from the mains plug socket for a few seconds and then power back up. The sensor should flash red/blue a few times as it reinitialises and then return to normal operation mode with a solid blue status light.
• The sensor is detecting a fault with the ATO pump. If the pump cannot run the sensor may go into alarm mode and turn off power to the pump. If this is the situation you will notice that when the top up activates the pump will not turn on and the status light will immediately show red and not flash blue until time out occurs. Disconnect the unit from mains power, check that the connector where the power lead and pump plug in to has not become wet and that the impellor in the pump is clean.
• Micro bubbles in the water are causing issues with the sensor detecting the water level. Check that the sensor is not in an area where it is subject to small bubbles, eg near the outlet from a skimmer.