How the Mid-Position Three Port Valve works. The spring pulls the valve to open the flow through port B (traditionally connected to the hot water cylinder's heating coil), while the motor winds it towards opening port A (feeding the radiator circuit).

How does a Drayton mid-position valve work?

Drayton mid-position valves allow the flow of water from the valve inlet to be directed to either of two outlets, or through both at the same time (mid-position). ... When the manual lever is moved to the right and pushed in to 'lock', both outlet ports A and B are open, it automatically releases when the valve is powered.

How does a 3 way heating valve work?

Three way valves

This type of three way motorised valve has port A normally closed with no power to the valve. In this state, water can flow from port AB to port B. When the electrical supply is activated, the actuator motor overcomes the force of the internal spring and closes port B.