The CLHS type fully automatic fuel (gas) hot water boiler adopts a fast installation vertical internal combustion three return fire tube structure. Adopting a bias furnace chamber wet back arrangement, high-temperature flue gas sequentially flushes the second and third return flue pipes, and then is discharged into the atmosphere through the chimney from the rear flue chamber. The boiler is equipped with world-renowned burners and adopts advanced technologies such as automatic proportional adjustment of combustion, automatic adjustment of feedwater, program start stop, and automatic operation. It also has automatic protection functions such as water temperature control, overheating, and overpressure shutdown. This type of boiler has the characteristics of compact structure, safety and reliability, easy operation, rapid installation, low pollution, low noise, and high efficiency. It is widely used for industrial steam and domestic heating in facilities such as enterprises, hotels, hospitals, office buildings, and civil buildings.