S-Plan Plus — Multi-Zone Wiring Guide
What This Covers
Standard S-plan uses two 2-port zone valves — one for central heating, one for hot water. Larger properties often add a third zone (commonly underfloor heating) and a secondary hot water circulation pump for instant hot water at distant outlets. This guide covers wiring a system with:
- Zone Valve 1 — Central Heating / Radiators
- Zone Valve 2 — Hot Water Cylinder
- Zone Valve 3 — Underfloor Heating
- Secondary Circulation Pump — on its own separate timer, independent of the CH/HW demand chain
S-plan plus: three 2-port zone valves feeding a multi-zone wiring centre, plus an independently timed secondary circulation pump. Wilsons Systems.
System Components
| Component | Function |
|---|---|
| Room thermostat | Controls the central heating zone valve |
| Cylinder thermostat | Controls the hot water zone valve |
| UFH zone thermostat | Controls the underfloor heating zone valve |
| Programmer / time clock | Sets on/off schedules for heating and hot water independently |
| 3-valve (or universal multi-zone) wiring centre | Combines the aux switch outputs from all three zone valves into a single boiler/pump demand — a standard 2-valve S-plan wiring centre only has two zone inputs and won't take a third |
| HW timer | Separate time switch controlling the secondary circulation pump — not part of the CH/HW programmer |
| Secondary circulation pump | Circulates already-hot water from the cylinder around a return loop so distant outlets get hot water instantly, instead of running the tap until it clears the pipe run |
| Boiler | Fires when at least one zone valve is open and signalling demand |
How It Works
- The programmer allows heating and/or hot water to call for heat, same as standard S-plan
- The UFH zone thermostat operates independently, calling its own zone valve the same way the room and cylinder thermostats do
- All three zone valves' auxiliary switches feed into the wiring centre, which fires the boiler and pump when any valve is open
- The secondary circulation pump runs only on its own timer — it does not call the boiler and isn't part of the demand chain. It simply moves water that's already hot around the return loop, so it only needs the cylinder to already be up to temperature.
Zone Valve Wiring
Same Honeywell/Drayton terminal pattern as standard S-plan — see the S-Plan Wiring Guide for the full terminal table. All three valves wire the same way; only the wiring centre changes to accept a third input.
Site Checks Before Wiring
- Confirm the wiring centre is rated for 3 zones. A standard 2-valve S-plan wiring centre has only two zone valve inputs — a 3-valve or universal multi-zone wiring centre is needed for the extra zone.
- Confirm what the UFH zone valve actually feeds. Wet underfloor heating usually runs through a manifold with its own blending valve and circulation pump, to protect the floor from the boiler's flow temperature. If that's the case here, the "zone valve" may really be a relay/interlock into the manifold's own pump pack rather than a plain 2-port valve wired the same way as the CH/HW zones — check what's specified before treating it as a like-for-like third zone valve.
- Decide whether the secondary pump should be interlocked to the HW zone valve's aux switch (so it can't run against a cold cylinder) or left purely timer-driven, per the original design intent.
Safe Working
- Isolate at the consumer unit before working — heating controls are typically on a 3A or 5A fused spur
- Photograph existing wiring before disconnecting anything
- Zone valve motors and pump connections carry mains voltage — always isolate before disconnecting terminals
- Never work on gas connections, the boiler heat exchanger, or burner