The utility model discloses a gravity change-over switch for a boiler. The gravity change-over switch particularly comprises a change-over cavity. Three flue gas channels are arranged outside the change-over cavity and are the auxiliary flue, the main flue and the flue gas outlet. The change-over cavity is provided with a turning plate capable of rotating. The turning plate seals the auxiliary flue or the main flue, it is guaranteed that the auxiliary flue or the main flue is communicated with the flue gas outlet, one side of the turning plate is provided with a balance weight, the weight of the balance weight is larger than the weight of the turning plate, and the gravity of the balance weight and the gravity of the turning plate are located on one side of the turning plate. According to the gravity change-over switch, flue gas is blown by a fan under the weight action of the balance weight to flow, change-over among exhaust flues of the boiler is achieved, manual operation is avoided, and the requirement for automated heating of the numerical control boiler is met.