|The CH ON signal from the
programmer would apply live to the white wire of the valve via the room
thermostat. Now that the cylinder temperature has been reached,
the cylinder thermostat changes over. The live which was feeding the
boiler via terminal 8 is now removed and is applied to the grey wire of
the valve via terminal 7.
The boiler shuts down briefly
while the valve now drives to the A position. Once this position is
reached, the live on the white wire (coming via the room thermostat) is
connected to the orange wire by a micro switch inside the valve. This
live signal now fires the boiler via terminal 8.
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