Central Heating Zone (2 port) valve

24 Jun 2008
Reaction score
United Kingdom
I am replacing a CH Zone (2 port) valve.
New Valve (Horstmann)
Blue = Neutral, Brown = "Call" terminal of room stat, Orange = Live
terminal pump & boiler, Grey = Live Supply, Green = Earth
Old Valve (Tower Heating Components A.C.L. Motortrol)
Blue = Motor, Brown = Motor, Green = Earth, Grey = Microswitch
White = another connection on the switch
Wires are very difficult to trace and colours vary. Can anyone help
with what should connect to what please.
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The Blue and Brown wires do the same job on both valves, so connect them exactly the same.

The grey is the same on both, so connect the new as the old.

The orange of the new valve is the same as the white of the old, so connect the same.

To explain.
The blue and brown wires are connected to the motor of the valve, which will run when the thermostat closes. This opens the valve and closes the switch connecting the grey to the orange. This supplies power to the boiler, which then runs.
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