Boiler Operation - Alpha CD24C Installation And Servicing Instructions

6

BOILER OPERATION

The boiler operating mode is controlled by the selector switch on the facia panel.
When set to , the boiler will only operate in the Domestic Hot Water mode. When set to
Domestic Hot Water and Central Heating mode.
Note: The clock (if fitted) only controls the operating times of the central heating, not domestic hot water - DHW is available continuously.
Domestic hot water supply always takes priority over central heating. If a demand for hot water is required during a central
heating period, the boiler will automatically switch to the hot water mode until the demand is satisfied. This interruption in the
central heating is only when the demand for hot water is present and should not be noticed by the User.
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 until the temperature within the boiler reduces
to the set temperature before allowing the burner to relight. 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.
If there is a demand for DHW during the burner delay, the boiler will operate to provide DHW until the tap is closed; the boiler
will then immediately revert to provide CH if there is a demand.
Note: If the system pressure is very low, the primary pressure switch will prevent the boiler from operating.
6.2 DOMESTIC HOT WATER MODE
When a demand for hot water (by opening a hot tap, etc.) is sensed by the flow switch, the pump starts and the burner lights,
increasing immediately to its maximum output. Water in the boiler is then diverted from the central heating system to the
domestic hot water heat exchanger, heating the incoming mains water. The burner output is varied to maintain the temperature
of the hot water as that set by the adjustable temperature selector. When the flow switch senses that hot water is no longer
required the burner is turned off and the boiler immediately returns to the central heating mode.
When the burner is turned off, the fan will continue to run for 50 seconds and the pump will stop immediately if the selector is
set for hot water only.
In both modes the fan modulates according to the output required.
6.3 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 8°C, providing the electrical supply is on and the selector switch is set to position 1 (
will operate until the water temperature in the system reaches approximately 40°C.
6.4 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 five minutes every 24 hours.
6.5 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.
, it will operate in the
) or position 2 (
Alpha CD24C/32C - Boiler Operation
). The boiler
21