During heating up or stirring of solutions uncontrolled splashes or overflowing of the solution can occur. In order not to overheat the inner parts of the unit the heating plate must be placed with a certain distance to the unit which results in relatively unprotected inner parts. For preventing the splashed or overflowing liquid from entering the inner part of the unit and possibly damaging the unit, the spill-proof drainage was designed, which leads the liquid outside of the unit where no damage can be done.