A submerged warmer is provided with a control box, a first control circuit board, an electric heater and a temperature sensor are arranged in the control box, and a waterproof body is arranged between the first control circuit board and the electric heater, The first control circuit board and the temperature sensor are connected to a plug. The plug is provided with a second control circuit board. The second control circuit board is provided with a power supply unit and a relay. The first control circuit board and the electric heater are integrated in the control box, and the waterproof body produces a waterproof effect to form a submerged structure, which reduces the winding of the wire and increases the aesthetics. The second control circuit board has a second protection effect. With the independent power supply unit and relay, the relay will be turned off when there is any abnormality in the first control circuit board, so that the first control circuit board has no power at all, and the aquarium pet environment can be maintained at the most appropriate temperature.一種沈水加溫器，設有一控制盒，於其控制盒內設有一第一控制電路板、一電熱器以及一溫度感應器，該第一控制電路板與該電熱器之間設一防水體，該第一控制電路板、該溫度感應器連接一插頭，該插頭設有一第二控制電路板，該第二控制電路板上設有一電源單元與一繼電器。藉由第一控制電路板、電熱器整合於控制盒內，由防水體產生防水作用，以形成沈水式構造，減少電線纏繞、增加美觀性；應用第二控制電路板具有第二道保護作用，藉由獨立狀之電源單元、繼電器，第一控制電路板不論何種異常時，繼電器會斷開，使第一控制電路板完全沒有電源，令水族寵物環境能保持在最適當溫度。
