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Mid-position valve

Used in Y-Plan systems, the mid-position valve is a 3-port valve. It can be powered to the domestic hot water side, the radiator side, or in mid-position open to both sides. It operates as follows:




Electrical Signal          -  Valve Position


No power to valve         -  Hot water only (port B)

240V on white wire         -  Hot water & heating (ports A & B)

240V on white and grey wires  -  Heating only (port A)

240v on grey wire only       -  Valve held in last position



The orange switched-live will become live when the valve is open to heating.



In a Y-plan system the underfloor heating takeoff should be plumbed before the mid-position valve, and a 2-port blocker valve should be fitted after the underfloor heating takeoff, and before the mid-position valve. This enables the underfloor heating to operate on its own, if neither the radiator circuit or the domestic hot water require heat.



The underfloor heating manifold is fully valved, so there is no need for a 2-port zone valve between the boiler and manifold.