Abstract: Apparatus for moving a vessel heater cover including upper linkage, lower linkage and a bell crank. The bell crank is pivotally secured to the upper and lower linkage. The lower linkage includes first and second pivot points. The first pivot point connects the lower linkage with the cover and the second pivot point connects the lower linkage with the connector link. A source of power is provided for effecting rotation of the connector link about the second pivot. Counterweights may be provided and be pivoted about the second pivot. The first pivot may include a gimbal providing two axes of rotation for the cover disposed generally perpendicular to each other. Compressible insulation in the cover may project downwardly to provide automatic sealing with the vessel cover. The mechanism provides automatic compensation for misalignment between the vessel rim and the cover.