What is the reason why there is no water in the water pipe of the old water bed when installing the

The reason why water leakage occurs is that the circulation of the heating system is not smooth, and the reasons for poor circulation are as follows: 1. There is gas at the high point of the system that cannot be released, resulting in suffocation. 2. The height difference between the radiator and the stove is small, making the natural circulation of heating water uneven. 3. Adding a bucket of water to the water inlet pipe can easily cause water to flow back. 4. The above reasons are based on the areas that require improvement within the reasonable installation of the heating system. The system does not respect the heating principle, which is not mentioned previously. I hope you understand if there is anything I can't say.