S-Plan · wiring diagram
S-Plan with a digital room stat wiring diagram
In short
An S-Plan is a fully pumped heating system with two 2-port motorised zone valves, one for central heating and one for hot water, driven by a programmer, a room thermostat and a cylinder thermostat. Each valve’s end switch feeds the boiler’s switched live, so the boiler fires only while a valve is open: the boiler interlock.
An S-Plan with a volt-free Digital Room Stat in place of the room thermostat.
An S-Plan wired in the simulator; this page’s circuit is listed wire by wire below. Wire colours as the lessons teach them. The meter reads what the circuit is doing.
The wiring centre, block by block
A block is a plain conductor: every wire landed on it is joined to every other, and to nothing else. The numbers are the habit the DrawWarm Method teaches, so the next engineer can read your work.
| Block | As the lessons teach it | Wired here |
|---|---|---|
| 1 | Permanent live from the fused spur, and both valves’ greys | Fused Spur L, Heat-Only Boiler L, 2-Port Valve (heating) G, 2-Port Valve (hot water) G, Dual Channel Programmer L |
| 2 | Neutral | Fused Spur N, Circulation Pump N, 2-Port Valve (heating) N, Heat-Only Boiler N, 2-Port Valve (hot water) N, Dual Channel Programmer N |
| 3 | Earth | Heat-Only Boiler E, 2-Port Valve (heating) E, 2-Port Valve (hot water) E, Dual Channel Programmer E, Fused Spur E, Circulation Pump E |
| 4 | Heating demand from the programmer, out to the room thermostat | Dual Channel Programmer 4, Digital Room Stat 1 |
| 5 | The room thermostat’s call, out to the heating valve’s brown | 2-Port Valve (heating) B, Digital Room Stat 2 |
| 6 | Hot water demand from the programmer, out to the cylinder thermostat | Cylinder Thermostat C, Dual Channel Programmer 3 |
| 8 | The cylinder thermostat’s call, out to the hot water valve’s brown | 2-Port Valve (hot water) B, Cylinder Thermostat 1 |
| 10 | The valves’ oranges in, the boiler’s switched live out | 2-Port Valve (heating) O, 2-Port Valve (hot water) O, Heat-Only Boiler SL |
Every wire, terminal by terminal
| From | Terminal | To | Terminal | Colour |
|---|---|---|---|---|
| Heat-Only Boiler | PL | Circulation Pump | L | Brown (live) |
| Heat-Only Boiler | E | Wiring Centre | 3 | Green/yellow (earth) |
| 2-Port Valve (heating) | E | Wiring Centre | 3 | Green/yellow (earth) |
| 2-Port Valve (hot water) | E | Wiring Centre | 3 | Green/yellow (earth) |
| Dual Channel Programmer | E | Wiring Centre | 3 | Green/yellow (earth) |
| Fused Spur | E | Wiring Centre | 3 | Green/yellow (earth) |
| Fused Spur | N | Wiring Centre | 2 | Blue (neutral) |
| Circulation Pump | N | Wiring Centre | 2 | Blue (neutral) |
| 2-Port Valve (heating) | N | Wiring Centre | 2 | Blue (neutral) |
| Heat-Only Boiler | N | Wiring Centre | 2 | Blue (neutral) |
| 2-Port Valve (hot water) | N | Wiring Centre | 2 | Blue (neutral) |
| Dual Channel Programmer | N | Wiring Centre | 2 | Blue (neutral) |
| Fused Spur | L | Wiring Centre | 1 | Brown (live) |
| Heat-Only Boiler | L | Wiring Centre | 1 | Brown (live) |
| 2-Port Valve (heating) | O | Wiring Centre | 10 | Orange |
| 2-Port Valve (hot water) | O | Wiring Centre | 10 | Orange |
| Wiring Centre | 4 | Dual Channel Programmer | 4 | Black |
| Cylinder Thermostat | C | Wiring Centre | 6 | Grey |
| Wiring Centre | 6 | Dual Channel Programmer | 3 | Grey |
| 2-Port Valve (hot water) | B | Wiring Centre | 8 | Brown (live) |
| 2-Port Valve (heating) | B | Wiring Centre | 5 | Brown (live) |
| 2-Port Valve (heating) | G | Wiring Centre | 1 | Grey |
| 2-Port Valve (hot water) | G | Wiring Centre | 1 | Grey |
| Circulation Pump | E | Wiring Centre | 3 | Green/yellow (earth) |
| Heat-Only Boiler | SL | Wiring Centre | 10 | Orange |
| Dual Channel Programmer | L | Wiring Centre | 1 | Brown (live) |
| Wiring Centre | 8 | Cylinder Thermostat | 1 | Brown (live) |
| Wiring Centre | 4 | Digital Room Stat | 1 | Black |
| Digital Room Stat | 2 | Wiring Centre | 5 | Brown (live) |
The truth table
Commissioning proves the system does what each demand asks, row by row, before it is handed over. Polarity and earth continuity come first.
| Demand | What the system does |
|---|---|
| No demand: programmer hot water off and heating off (room stat calling, cylinder cold) | Both valves stay closed; boiler off |
| Heating only: programmer heating on (room stat calling, cylinder cold) | Heating valve opens, hot water valve stays closed; boiler fires and the pump runs |
| Hot water only: programmer hot water on (room stat calling, cylinder cold) | Hot water valve opens, heating valve stays closed; boiler fires and the pump runs |
| Heating and hot water: programmer both on (room stat calling, cylinder cold) | Both valves open; boiler fires and the pump runs |
| Programmer both on, both stats satisfied | Both valves closed; boiler off |
Where it connects
Other systems
- S-Plan
S-Plan
- Wireless S-Plan
S-Plan
- S-Plan with a frost thermostat
S-Plan
- S-Plan Plus
S-Plan
- Y-Plan
Y-Plan
- Y-Plan with a frost thermostat
Y-Plan
- Combi boiler with a wireless thermostat
Combi
- Combi boiler with two heating zones
Combi
Back to every wiring diagram.
If this is your home: this page is written for heating engineers. Mains wiring and gas appliances are not DIY jobs; call a Gas Safe registered engineer. If you smell gas, leave the building and call the National Gas Emergency Service on 0800 111 999.
Practise it in the simulator.
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