Solar overflow pipe prevents water from overflowing

Solar overflow pipe continues to overflow: water flows when water is filled;

Solar overflow pipe continues to overflow, indicating that the system is still adding water the water. Your water fill valve may be malfunctioning.

You can open the hot water valve (turn off the cold water) for inspection: if the hot water flows more when it is opened to the maximum and the overflow stops after when it closes, it overflows; again there is a problem with the water add valve.