When the two buttons are flashing together, this means the unit needs to be descaled. To start the descaling process, add 100 mL (3.3 fl oz) of descaling solution to the water tank and fill the rest with water. Push and hold the two buttons for 2 seconds and the unit will start to brew. When the brewing process is finished, remove and wash the water tank. You must now brew two fresh pots of water only through the system to remove any residual descaler.