The diagram can be used as a boiler with a pump overrun as well you just take the pump live neutral earth from the wiring center and run it to the boiler terminals. The 2 port valve has one live supply to motor it open when called to by the particular service it supplies.

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S plan wiring diagram with pump overrun. Soon you should feel some hot water in your radiators. S plan wiring c plan schematic gravity hot water controlled by a 6 wire valve not your standard 5 wire valve and a pumped central heating circuit controlled by a thermostat. Part 2 in the series looks at s plan wiring a system which uses two separate valves. Here coloured wires indicate the permanent mains supply to the boiler and programmer. Boiler and pump receive live supply and operate. However when used as a pump overrun using 4 core flex from the wiring centre the mor and bor terminals would each have a live connection permanent live and switched liveand the pump live would be connected to the common terminal.
This diagram shows the wiring layout using the most typical components. Heating controls wiring guide issue 17 v4073a y plan how a mid position valve operates within a y plan heating system how a w plan heating system operates. This video covers the wiring and electrical operation of an s plan system with two 2 port valves. Wiring diagrams and further information continues below. One valve for hot water another for heating. Electrical wiring for central heating systems.
Its just a guideline on how the average boiler is wired. It can be adapted how you need it. There is a diagram on the taco web. Faq wiring diagram y plan pump overrun st and dt92e faq wiring diagram s plan pump overrun st and dt92e faq wiring diagram s plan plus pump overrun st and dt92e faq wiring diagram combination boiler st honeywell t4 additional wiring diagrams lyric t6 additional wiring diagrams v zone valve s plan. A great advantage of s plan systems over y plan systems is the opportunity to have more than two zones.