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GAS CONTROLS
Control is by automatic ignition of intermittent pilot; once the
presence of a flame has been proved the single (or double)
main gas valves open to give full heat input. The mains voltage
supply is via a terminal plug connection at the control box.
ELECTRICAL CONTROLS
The boiler is supplied with 2 printed circuit boards; Board
S4561B1054 is the ignition board containing the flame proving
logic and the on-board spark generator. Board W4115A1020
contains the electronic thermostat and the pump overrun timer. A
preset overheat thermostat is also fitted. The control box displays
neons indicating boiler status as follows:
Boiler on
Lockout
Overheat
A 4 minute anticycle delay is built in to the controls to prevent
rapid cycling.
FROST PROTECTION
Frost protection is incorporated in the boiler as long as there is a
permanent live supply wired to terminal L1 on the terminal plug-
in connection at the control box and the boiler thermostat knob is
not switched to off.
If the temperature sensed by the boiler thermostat falls to about
o
5
C the boiler will fire until the temperature reaches 18
that this is designed to protect the boiler and may not necessarily
protect the remote parts of the system.
OPTION KITS
Remote indication kit
This kit gives the facility of remote indication of the boiler status.
Pressure gauge kit
In addition to the above control kit, an optional pressure gauge
is also available for the range of boilers. Details for fitting are
included with the pressure gauge.
1
WATER CONNECTIONS
Flow and return connections are 2" BSP.
A 1" BSP tapping is provided in the redundant return flange for
the cold feed or expansion vessel connection.
Safety Valve
A safety valve must be sized and fitted in accordance with BS.
6644 for every type of system. The valve should be set at 0.7
bar (10 lb/in.
) above the operating pressure in the boiler. The
2
maximum safety valve setting is 0.7 bar (10 lb/in.
maximum design operating pressure of 6 bar (87 lb/in.
Cold Feed/Open Vent
The independent cold feed and the open vent must comply
with BS. 6644 and be of the following minimum size.
Boiler Size
CXA 40 - 50
CXA 60 -120
Sealed system filling point - refer to Frame 8
Concord CXA -
Installation and Servicing
2
) above the
Cold Feed
Open Vent
"
1"
3/4
1"
1
"
1/4
GENERAL
Downdraught thermostat kit
This kit is optional when used on a single CXA installation, but
mandatory when used on a multiple boiler installation.
DUTY
The range of boilers is suitable for: Combined indirect pumped
domestic hot water and central heating systems; Independent
indirect pumped domestic hot water or central heating systems.
Fully pumped systems may be open vented or sealed.
The range of boilers is NOT suitable for:
1. Gravity DHW systems.
2. Gravity heating systems.
3. Direct domestic hot water supply.
WATER CIRCULATION SYSTEM
Due to the compact nature of the boiler the heat stored within the
castings at the point of shutdown of the burner must be dissipated
into the water circuit in order to avoid the overheat thermostat
tripping. In order to allow pump operation after burner shutdown
the boiler control box incorporates a pump overrun facility which
operates for approximately 6 minutes after burner shutdown and,
in order to make use of this, the pump must be wired to the
appropriate terminal L2 (pump) in the boiler control box.
1. The minimum flow rate as given in Table 4 must be
maintained whenever the boiler is firing and during the
pump overrun period.
o
C. Note
2. During the period of pump overrun there must be an open
circuit of adequate water volume and/or load. The
minimum size of this circuit is given by the use of Graph 1.
Examples shown on Graph 1
a. For the CXA 90 and CXA 100 the minimum circuit during
pump overrun could be a load of 6 kW with a volume of 31
litres or any other combination given by the relevant line.
b. For the CXA 70 and CXA 80 the minimum circuit during
pump overrun could be a load of 2 kW with a volume of 45
litres or any other combination given by the relevant line.
).
2
5
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