Varitech have just released an upgrade to their current hot water system.
It consists of a new digital controller which lets you increase or decrease your water flow in small (100) increments. The controller shows you your current battery voltage and working voltage. It also allows you to monitor water temp and external temp.
The hose ends are connected back to the tank and the frost protection switch is activated at the end of the day. If the external temp drops sufficiently the heater and pump will circulate hot water through the system and back into the tank until the water temp rises enough to avoid freezing. This only takes a few minutes to achieve at the heater can reach a temp of 80 degrees c. So the system will offer true and efficient frost protection for all of your system including hoses.