What is frost protection? How does it activate?

Frost protection of your device activates once output temperature of central heating system water drops below 5°C and your device keeps operating until it rises up to 15°C. The following conditions must be met for activation of frost protection. o Power supply of your device must be switched on and the device must be in 'ON' or 'Summer' condition. o Gas valve and radiator valves must be open. o Central heating system must have proper water pressure.