9
SYSTEM BOILER WITH EXISTING CONTROLS
System Boiler with existing 2 channel programmer and optional Thermostat
**Before commencing, take clear photos of the existing programmer wiring**
S Plan (2 x 2 port zone valves, usually near hot water cylinder)
Usually 4 Wires to existing programmer, Live, Neutral, CH ON, HW ON. (CH OFF and
HW OFF not used)
Y plan (1 x 3 port zone valve, usually near the hot water cylinder)
Usually 5 wires to existing programmer, Live, Neutral, CH ON, HW ON, HW OFF. (CH
OFF not used)
Existing programmers will usually have 6 or 8 terminals (Plus possibly an earth
terminal)
There should also be a wiring schematic on the existing programmer (see
Fig 8
).
Using this schematic, identify and label each wire according to its function
, e.g.
Live, Neutral, CH ON/OFF, HW ON/OFF etc. If the programmer has 8 terminals, with
‘C’, ‘Com’ or ‘Common’ AND these terminals are linked to Live, then ignore the links
and identify the remaining wires. If the existing programmer uses the notation NO
(Normally Open) & NC (Normally Closed), NO = ON and NC = OFF
Fig 8
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