Water level float switch error

You do not mention the model, I presume that it is a cassette, in which case the float switch is located in the indoor unit. You have to remove the cover which is 4 screws. First make sure all power supply is turned off. Then remove the drain pan which surrounds the fan blade. You will see in one corner of the unit a slightly deeper part of the drainpan, this is the corner where both the condensate pump as well as float switch is located. Before you do any of this, give a serious blow into the drain pipe from outside and this may dislodge any sludge which may be causing the floatswitch to stick. You can also pull out a rubber plug which is under the pump on the drainpan.