What is a Central Heating Motorized Valve?

A motorized valve is a valve in a water pipe which can be turned on or off by an electric motor.
The wire from the electric motor runs to the wiring centre which is usually in the airing cupboard.
A motorized valve is one of the heating controls for the central heating system.

A motorized valve can be a 2 port valve or a 3 port valve.

A 2 port valve (also called a zone valve) has two 22mm pipes connected to it.
It is a simple on or off valve which is used to direct heating water from the boiler.
Two 2 port valves are needed to control a central heating system.
The first 2 port valve controls the flow of heating water to the hot water cylinder
and the second 2 port valve controls the flow of heating water to the radiator circuit.
This arrangement of valves is often called S plan (after the Honeywell Sundial plans).

A 3 port valve (also called a mid-position valve) has three 22mm pipes connected to it.
Only one 3 port valve is needed to control a central heating system.
It is a 3 way valve which is used to direct heating water from the boiler.
In the first position it directs the flow of heating water to the hot water cylinder.
In the second position it directs the flow of heating water to the radiator circuit.
In the third (mid-way position) it directs heating water to both the hot water cylinder and radiators.
This arrangement of valves is often called Y plan (after the Honeywell Sundial plans).

If a motorized valve stops working it can sometimes be repaired by replacing the motor
on top of the valve (often called replacing the head). On most modern valves the
motor can be replaced without draining down the central heating water.

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