Electrical - Worcester WM 12 Installation And Servicing Instructions

10. Electrical

(See Figs. 15 to 22).
10.1 The electrical supply to this appliance must satisfy the latest
edition IEE Wiring Regulations and any local regulations which apply.
The method of connection must allow complete isolation of the
appliance and the supply to the boiler must be the only electrical
supply to the system. This ensures the safety of a single fused sup-
ply.
NOTE: The appliance could provide an external electrical supply
for servicing and should therefore be fed via a separate circuit
breaker including earth leakage protection.
10.2 To gain access to the electrical terminal strip.
1. Isolate the mains electrical supply.
2. Remove the cabinet as described in section 5.1.
3. Release the two screws securing the facia to electri-
cal control box and pivot the facia down. Remove the internal
electrical box as described in Section 5.2.
10.3 Mains Wiring
Mains supply – 230 V AC ~ 50 Hz, 5A External Fuse to BS1362.
LIVE - Brown, NEUTRAL - Blue, EARTH - Green/Yellow
Mains Cable: 0.75mm 2 (24 x 0.20 mm) to BS 6500 Table 16.
The mains supply cable should be connected into the terminals
marked L (Live), N (Neutral) and E (Earth) on the appliance termi-
nal strip and securely held in the cable clamp located just below
the L (Live), N (Neutral) and E (Earth) terminals at the rear of the
electrical box . To secure the cable, remove the clamp retaining
screw and pull its inner body out to allow the cable to be fed
through. With the cable in position refit the screw and fully tight-
en to grip the cable. Feed the cable out of the appliance and
route to the connection point avoiding any hot surfaces.
The appliance must be earthed.
10.4 Programmer
(See Fig. 16, 18, 21).
A plug in, colour co-ordinated, 2 channel electronic programmer is avail-
able from Worcester, Bosch Group. Full instructions covering installation
and operation of the programmer are included with the kit.
The programmer will give fully independent central heating (CH) and hot
water (HW) programmes when the switch on the rear of the unit is set to P.
If an external programmer is to be fitted to the boiler the link
should be removed from the programmer plug Connection (7 to
9) and wired as shown in Fig. 16.
10.5 Safety Check
In the event of an electrical fault after the installation of the
appliance, the electrical system shall be checked for short cir-
cuits, fuse failure or incorrect polarity of connections.
10.6 Basic Control (Room Thermostat)
(See Fig. 16).
As supplied the boiler will give a fully pumped heating circuit . The
central heating temperature is controlled by the boiler control
thermostat. Additional control may be obtained by the use of a
room thermostat, having removed the link from terminal 2 to 4.
The pump should be connected to the boiler terminal block as
shown in Fig.16. This will allow the pump to operate with the
service switch set to the 'SERVICE' mode.
10.7 Honeywell "S" Plan (See Fig. 20, 21, 22)
NOTE: When wiring the appliance to a Honeywell 'S' Plan only
use the wiring diagrams in these instructions. Use a Honeywell
10 way junction box (Part No. 42002116-001), the Honeywell
wiring centre (Part No. 42005748-001) should not be used.
The "S" plan provides complete control on installations having
pumped circulation to both the domestic hot water and radiator
circuits.
The domestic hot water and radiator circuits are independently
controlled by two motorised valves via a cylinder thermostat
and a room thermostat. Both thermostats switch the water cir-
culator and the boiler on and off.
10.8 Honeywell "Y" Plan (See Fig. 17, 18, 19)
NOTE: When wiring the appliance to a Honeywell 'Y' Plan only
use the wiring diagrams in these instructions. Use a Honeywell
10 way junction box (Part No. 42002116-001), the Honeywell
wiring centre (Part No. 42005748-001) should not be used.
The "Y" Plan provides complete control on installations having pumped
circulation to both the domestic hot water cylinder and radiator circuits.
The domestic hot water and radiator circuits are controlled by a
3 port motorised valve via a cylinder thermostat and a room
thermostat. Water flow is diverted to either circuit or to both cir-
cuits at the same time. Both thermostats switch the water circu-
lator and the boiler on and off.
Note: The "Y" plan requires a live feed from the hot water "off"
switch position. In order to achieve this, using a Worcester pro-
grammer, remove the orange wire from terminal 9 and pull back
through the tie wraps. Do not attempt to cut the tie wraps.
Ensure that the brown wire is firmly secured in terminal 9.
Connect the orange wire to terminal 6.
10.9 Frost Protection
The appliance is supplied with a frost thermostat that is
attached the heat-exchanger, this protects the appliance only.
For full frost protection of the property a single pole frost ther-
mostat should be fitted so that both the boiler and the circulat-
ing pump/control circuits are energised under frost conditions
as shown in the individual control systems. (See Fig. 16, 19 and 22).
10.11 Service Switch (see Fig. 29)
A service switch has been provided next to the burner to allow the ser-
vice engineer to control the burner operation from outside the property.
The engineer should have access to the property to set the heating sys-
tem controls to give a central heating demand so that the heat generat-
ed during the burner testing can be dissipated. However, in the event
that the controls cannot be accessed a service position is available on
the switch to enable the burner to be fired. The ability to dissipate the
heat in this mode will depend on which control system has been
installed and is described below for the systems specified in 10.6 to 10.8.
The switch settings are:
(a) 'RUN' mode – Under normal operating conditions the appli-
ance will be controlled by the programmer. The switch in this
position will appear black.
(b) 'OFF' Mode - The appliance will not operate unless there is a
demand via the frost thermostat. The switch in this position will
show a small amount of red.
(c) 'SERVICE' Mode - Allows the service engineer to override
the programmer to test fire the burner where there is no access
to the system controls and the burner will not fire. The switch in
this position will appear red.
NOTE: This mode is optional when servicing and should only be
used where access to the system controls is unavailable.
The service mode will give the following minimum control:
(i) Basic Control. (See Section 10.6)
Full system control will be gained.
(ii) Honeywell "Y" plan. (See Fig 17, 18, 19)
The pump and burner will operate and heat will be
dumped to the hot water tank if the time control is 'OFF' or to
the heating circuit/hot water tank if the time control is 'ON'
depending on the last demand made by the system.
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