Motorised valve: what is it & how does it work?

A motorised valve is a central heating system component which controls whether hot water from the boiler is used to heat the radiators, or the water in the hot water cylinder for the taps. It is usually found adjacent to the hot water cylinder, e.g., in the airing cupboard. As the name implies, it is electronically operated. Prolific manufacturers of motorised valves include Honeywell and Drayton.

Motorised valve overview

In a typical indirect hot water system, the boiler provides the hot water for both the radiators and the taps. In order to heat the water for the taps, water from the boiler flows through a coil of copper pipe inside the hot water cylinder, heating the water inside. The motorised valve is used to control whether hot water from the boiler flows through the radiators or through the cylinder coil.

The valve itself is operated by the thermostat and is made out of brass. Pipes are connected to the valve by two or more compression fittings. The motor itself is contained in a steel or plastic housing, known as the actuator. This can be separated from the valve independently, meaning that it is not necessary to drain down the system and disconnect the valve when replacing a faulty motor/actuator.

Motorised valve types

3 port / ‘Y’ Plan system

There are several different types of motorised valve available. The most common is the 3 port motorised valve. It has three pipe connections and is in a ‘T’ or ‘Y’ shape. Hot water from the boiler enters the valve via the central connection. The two outlets are designated A and B. The outlet which diverts water through the coil can easily be identified as the outlet directly connected to the cylinder. This configuration is known as a ‘Y’ plan system.

There are two different kinds of 3 port valve. A mid-position valve allows water to pass through both ports at the same time. In other words, this allows the boiler to heat the hot water cylinder and the radiators simultaneously. On the other hand, a diverter valve does not – when port A is open, port B is closed, and vice versa.

2 port / ‘S’ Plan system

A 2 port motorised valve has two connections: an inlet and an outlet. When the valve is closed, water cannot flow through it.

The principal of operation is exactly the same, except that two valves are necessary. This means that:

  • With the valve to the cylinder coil open and the valve to the radiators closed, hot water from the boiler will flow through the coil.
  • With the valve to the coil closed and the valve to the radiators open, water will flow through the radiators.

However, the advantage of ‘S’ plan systems is that they allow for separate heating zones in larger properties, e.g. upstairs and downstairs rooms.