The present disclosure discloses a water heater, and a scale detection system and method. The scale detection system comprises: a first temperature detector configured to acquire a first temperature of a heat exchange zone of a water heating device; a second temperature detector configured to acquire a second temperature indicating a water temperature in the water heating device; and a controller in communication with the first temperature detector and the second temperature detector, and configured to acquire a temperature difference between the first temperature and the second temperature based on the first temperature acquired by the first temperature detector and the second temperature acquired by the second temperature detector, and determine that a scale generation amount in the water heating device reaches a preset threshold when at least one of the following judgment conditions is met: the first temperature is not less than a preset temperature threshold; and the temperature difference is not less than a preset temperature difference threshold. The present disclosure can ensure that a user can be reliably and timely reminded to clean the scale under different working conditions.