S-Plan Wiring Reference Pack

S-Plan Heating System Wiring Reference

Overview

S-Plan systems use separate 2-port valves for heating and hot water control.

Main Components

• Boiler
• Programmer / timer
• Room thermostat
• Cylinder thermostat
• 2 × 2-port motorised zone valves (heating + hot water)
• Pump
• Junction box / wiring centre

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System Operation

• Heating and hot water are independently controlled.
• Each zone has its own valve.
• Each valve provides a separate boiler demand signal.

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Wiring Concept (Signal Flow)

• Programmer sends switched live to each zone
• Thermostat/cylinder thermostat controls valve opening
• End switch in each valve signals boiler demand

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Key Wiring Points

• Heating valve controls radiator circuit
• Hot water valve controls cylinder circuit
• Either valve end switch can trigger boiler
• Neutral connections commoned in wiring centre
• Earth continuity maintained across all components

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Common Fault Areas

• One zone not opening (failed actuator)
• No boiler firing (end switch fault)
• Crossed heating/hot water controls
• Incorrect programmer configuration
• Sticking valve heads
• Wiring centre misconnection after maintenance

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Notes

• S-Plan is easier to fault-find than Y-Plan due to separate zones.
• Always isolate valves before replacing heads.