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230V 50Hz
fused 3A maximum
L N E
1
2
2
1
E
N L
Terminal Block
L
N
Relay
PCB
Board
Baxi System
Boiler
Scheme 4
24
3 Port Valve
2 Position
b
g/y
w
Room
gr
A
Thermostat
o
AB
2
1
3
3
4
5
6
7
8
L
N
HTG
HW On
HW Off
Timer
b
- blue
w - white
o
- orange
gr - grey
g/y - green/yellow
8.9
Scheme 4
Cylinder
Thermostat
24. Scheme 4 utilises an existing 3 port mid
position zone valve and is based on a 'Y' plan
1
B
system but with significant changes. The zone
valve operates as a two position type and the
C 2
boiler is controlled as in Scheme 3.
25. To convert a standard 'Y' plan to Scheme 4
proceed as follows:-
9
10
i) Change the orientation of the zone valve so
that port 'A' serves domestic hot water and port
'B' the central heating.
ii) Remove the wire between 7 on the terminal
strip and terminal 2 of the cylinder thermostat.
3
1
Frost
iii) Disconnect the orange zone valve wire from 8
Thermostat
on the terminal strip and connect to 9.
iv) Disconnect the grey zone valve wire from 7
on the terminal strip and connect to 8.
v) Disconnect the white zone valve wire from 5
on the terminal strip and connect to 8.
vi) Connect 8 on the terminal strip to switched
live on the domestic hot water relay PCB.
vii) Connect 5 on the terminal strip to terminal 2
of the boiler terminal block.
26. For isolation purposes both the orange zone
valve wire and the live signal from the timer to
close the domestic hot water port of the zone
valve are connected to "dead" points on the
terminal strip.
8.0 Installation
System Wiring (cont)
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