Thermosiphon solar collectors provides mains pressure pre-heating via a high efficiency copper coil heat exchanger located within the solar collector tank. The way in which the Mains Pressure solar collector heats water is the same as the Non pressure solar collector. Rather than using the water in the tank directly, as the Non pressure does, the type uses a 45～60 copper coil heat exchanger inside the tank which provides more than 1.2mP2P of heat transfer area. When water flows though the coil it absorbs heat from the water inside the solar collector tank. The solar collector tank is therefore a thermal store.