5 OPERATION MODES Winter Conditions - (Central Heating and Domestic Hot Water required) Set the mode knob (C) ‘ ’ (winter. The boiler will fire and supply heat to the radiators. The domestic hot water preheat will operate with the preheat button set to ‘Preheat On’. Summer Conditions - (Domestic Hot Water only required) Set the mode knob (C) to ‘ ’ (summer. Set the central heating demand on the external controls to OFF. The domestic hot water preheat will operate with the preheat button set to ‘Hot Water On’. Boiler Off Set the mode knob (C) to BOILER OFF. The boiler mains power supply must be left onto enable frost protection (see Frost Protection). PREHEAT - DOMESTIC HOT WATER The domestic hot water heat exchanger within the boiler can be kept preheated to provide faster delivery of hot water at the tap. This is achieved by pressing the preheat button to “Preheat On”. The boiler will operate periodically fora few seconds to maintain the domestic hot water heat exchanger in a preheated condition. The average time period between operation is 90 minutes. This may vary considerably due to the surrounding ambient temperature of the boiler. The boiler will operate whenever there is a demand for domestic hot water. If standard hot water delivery is satisfactory set the preheat to ‘Preheat Off’.