A level sensor assembly (10) for measuring physical properties indicative of a quality of a urea solution (AdBlue/DEF), where at least a portion of said level sensor assembly (10) is inserted in a tank (50), said level sensor assembly (10) comprises a header unit (12) mounted in an aperture of the tank (50); heating tubes (20) inserted in the tank for heating/thawing the urea solution in the tank (50) and one or more tubes (22) for suction of urea solution from the tank (50), said tubes (20,22) being connected to the header unit (12); and a level sensor (24,26) for measuring level of urea solution in the tank (50). Further, a detachable UQS sensor (30) is installed in the header unit (12), said UQS sensor (30) being at least partly submerged in a liquid pool (32) of urea solution in the header unit (12), and the liquid pool (32) in the header unit (12) comprises a compressible and/or expanding bottom (34).