There are two reasons for hot water backflow in solar water heater：
1. For the solar water heater installed on the top floor, when the tap water pressure is low, open the water valve, and the hot water in the water heater will immediately flow into the tap water pipe, forming hot water backflow in solar water heater.
2. After being heated by solar water heater, the water temperature can reach 95 degrees. Nowadays, most domestic water supply pipes are made of PP-R pipe, which is also called three type polypropylene pipe. The heat-resistant temperature is 70 degrees. Therefore, under high temperature, the pipes are easy to soften, reduce the pressure value and burst.
If the water heater is equipped with a check valve, it can prevent the hot water backflow in solar water heater. If backflow occurs to users who have installed check valve, it is caused by incorrect installation position or check valve failure.