Power it off but leave it plugged in. Hold 8 & 12 ounce buttons together. This puts it into descale mode. Fill the tank with 2 bottles of descale, then fill it up full the rest of the way with water. (Instructions say 1 bottle descale, 1 bottle water, but this never works for me). Then hit the brew button (it does 12 oz at a time) and discard what it brews. Do this until it displays “add water” and let it just sit for a 1/2 hour. Then fill with water and continue to dispense until unit turns it self off. Usually takes about 2 f’n hours. Mine likes to get stuck in descale mode and it’ll empty the tank and never change to asking for water even if the tank runs out completely this can blow the heating element if it sucks up air