You can have W, S, Y, and C plans. The Honeywell site has details of all plans.
The S uses two motorised valves one for domestic hot water the other for central heating and lends itself to expanding into S plus with zone heating.
The Y uses a single valve with a mid position but is not as easy to expand to add zones and you canâ€™t normally select on a programmer central heating only although why one would want to I do not know. Both central heating and hot water can run together.
The W plan very like Y plan but either hot water or central heating not both together
The C plan domestic hot water is not pumped.
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