The invention relates to a release device for a rear seat backrest component part of a vehicle seat, comprisinga housing to attach to the foldable rear seat backrest component, a handle connected to a transfer means and designed to be actuated by the user, anda warning indicator, including an indicator area to indicate the unlocked state of a lock in a pushed-forward position. The pump piston has a reduced diameter portion which provides a primary piston. The control device can judge the presence of the water in the water tank according to the empiric value of the actual heating system, preventing the pump from damage due to empty pumped. Form-dependent or topographical characteristics, such as scratches, are derived from a second image data set formed with glancing light or oblique light.