Alpha Alpha CB24, Installation And Servicing Instructions, Page: 17 / 36

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3. Seasonality valve - CB24 and CB28 only: Set the seasonality valve (see Fig. 11) to the User's requirements, i.e. to the
required temperature of hot water from the tap. This is achieved by fully opening a hot water tap and turning the adjusting
screw (access hole in front of bottom tray) with a screwdriver. Anticlockwise to increase the temperature and clockwise to
decrease.
Note: Check the hot water temperature before adjusting the screw - it may be set correctly.
Once set no further adjustment should be required. The valve will automatically adjust the flow rate for summer and winter conditions.
4. If the boiler is not to be handed over immediately, close the boiler gas service cock and switch off the electrical supply.
5. If there is any possibility of the boiler being left during frost conditions, then the boiler and system should be drained (refer to section
8.2). It is recommended that a label is attached to the boiler drawing attention to the fact that the system has been drained.
6. Complete the details of the installation on the back page of this manual and the Benchmark log book.
5.8 USER INFORMATION
The User must be advised (and demonstrated if necessary) of the following important points:-
1. How to light and turn off the boiler and how to operate the system controls.
2. The importance of annual servicing of the boiler to ensure safe and efficient operation.
3. That any servicing or replacement of parts must only be carried out by CORGI registered personnel.
4. Ensure that the boiler controls and room thermostat (if fitted) are set to the User's requirements.
5. Tell the User about the sealed system pressure.
6. Tell the User that if the electrical supply is on and the boiler has not operated for 24 hours for heating or hot water, the
pump will automatically operate for 5 minutes.
7. Explain to the User that an internal frost thermostat is fitted in the boiler, and that the electrical supply to the boiler must be
left on for the thermostat to operate.
8. Show the User the position of the pressure relief valve discharge pipe.
9. Hand the User's instructions and the Benchmark Log Book to the User.
10. Leave these Installation and Servicing instructions with the User for use on future calls.
11. Inform the User that the boiler bottom tray has the facility to store the instructions and log book.
Alpha CB24/28 - Commissioning/Boiler Operation
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 , it will operate in the 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 at full speed; once the air pressure
switch is proved the 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 selector, the burner output is reduced. When the set
temperature is reached, the burner is turned off. The fan continues to run for 20 seconds and the pump continues to run for three
minutes to remove residual heat build up in the boiler before allowing the burner to relight. If the CH 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 20 seconds and the
pump continues to run for 30 seconds. In this instance there is no 3 minute delay before the burner will relight.
If there is a demand for DHW during the 3 minute 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 at
its middle output, 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.
In both modes the fan operates at full speed before the burner lights, remaining at that speed until the demand is satisfied.
When the burner is turned off, the fan will continue to run for 20 seconds and the pump will stop immediately if the selector is
set for hot water only.