Alpha CD12S - Boiler Operation

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6.1 CENTRAL HEATING MODE
If there is a call for heat, the pump will start to circulate the central heating water. The fan will run and the pre-mix burner will
light. The burner output then automatically adjusts to suit the system demand; as the temperature of the water in the boiler
approaches that set by the adjustable temperature thermostat, the burner output is reduced. When the set temperature is
reached, the burner is turned off. The fan continues to run for 50 seconds and the pump continues to run for three minutes,
after which the burner can relight if required. If the primary sensor has not registered the pre-set temperature but the room
thermostat is satisfied the burner is turned off. The fan continues to run for 50 seconds and the pump continues to run for 60
seconds. In this instance there is no delay before the burner will relight.
Note: If the system pressure is very low, the primary pressure switch will prevent the boiler from operating.
6.2 FROST THERMOSTAT
The boiler incorporates a built in frost thermostat which automatically turns on the boiler and pump if the water in the boiler
falls below 4°C, providing the electrical supply is on and the selector switch is set to position 1 or position 2. The boiler will
operate until the water temperature in the system reaches approximately 30°C.
Any other pipework outside the boiler should be protected from the risk of freezing and protected with insulation. Additional
protection from an external frost thermostat and pipe thermostat should also be considered.
6.3 PUMP
If the electrical supply is on and the boiler has not operated for 24 hours for heating or hot water, the pump will operate
automatically for thirty seconds every 24 hours.
6.4 INDICATOR NEONS
When neons A (red), B (red), C (yellow), D (green) are illuminated, the following conditions apply:-
Neon
D Illuminated continuously - Electricity supply to the boiler is on.
C Illuminated continuously - Burner is alight.
A Flashing on and off - Temperature sensor fault.
B Flashing on and off - Overheat thermostat has operated. Rotate selector switch to the reset position (3) to reset.
B Illuminated continuously - Burner has failed to light. Rotate selector switch to the reset position (3) and the
ignition sequence will restart after a delay of about 30 seconds.
A and B Flashing on and off at the same time - Blocked flue or fan fault.
A and B Flashing on and off alternatively - System pressure is very low and re-pressurisation is required.
A Flashing and B Illuminated continuously - Pump fault or restricted flow.
Note: Do not hold the selector switch in the reset position (3) for more than 2 to 3 seconds.
Alpha CD12S/20S/28S - Boiler Operation
6 BOILER OPERATION