Display shows L0 or a similar low-temperature/anti-freeze indication; the burner may fire briefly without hot water demand.

Safety: This is usually a normal protective function.

• Check location: Ensure the heater is installed in a frost-protected area or that the room is adequately heated.
• Insulate pipes: Insulate exposed water pipes to reduce heat loss and prevent freezing.
• Sensor check: If L0 appears in warm conditions, have a technician check the relevant temperature sensors.