Y-Plan · wiring diagram
Y-Plan wiring diagram
In short
A Y-Plan is a fully pumped system with one 3-port mid-position valve. It rests at the hot water port, moves to mid-position when the room thermostat calls, and to the heating-only port when hot water is satisfied or timed off. The white and grey cores drive it; the orange core and the cylinder stat fire the boiler.
A complete Y-Plan: one three-port mid-position valve, with a cylinder thermostat (C from block 6, its call 1 to block 8, its satisfied 2 to block 7).
This circuit, wired in the simulator. 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 | Fused Spur L, Dual Channel Programmer L, Heat-Only Boiler L |
| 2 | Neutral | Fused Spur N, Circulation Pump N, Room Thermostat N, Dual Channel Programmer N, Heat-Only Boiler N, 3-Port Valve N |
| 3 | Earth | Fused Spur E, Circulation Pump E, Dual Channel Programmer E, Heat-Only Boiler E, 3-Port Valve E |
| 4 | Heating demand from the programmer, out to the room thermostat | Dual Channel Programmer 4, Room Thermostat L |
| 5 | The room thermostat’s call, out to the valve’s white | Room Thermostat SL, 3-Port Valve W |
| 6 | Hot water demand from the programmer, out to the cylinder thermostat | Dual Channel Programmer 3, Cylinder Thermostat C |
| 7 | Hot water not wanted (the programmer’s hot water off and the cylinder thermostat satisfied), out to the valve’s grey | Dual Channel Programmer 1, 3-Port Valve G, Cylinder Thermostat 2 |
| 8 | Hot water wanted (the cylinder thermostat’s call) and the valve’s orange, out to the boiler’s switched live | Cylinder Thermostat 1, Heat-Only Boiler SL, 3-Port Valve O |
Every wire, terminal by terminal
| From | Terminal | To | Terminal | Colour |
|---|---|---|---|---|
| Fused Spur | L | Wiring Centre | 1 | Brown (live) |
| Fused Spur | N | Wiring Centre | 2 | Blue (neutral) |
| Fused Spur | E | Wiring Centre | 3 | Green/yellow (earth) |
| Circulation Pump | E | Wiring Centre | 3 | Green/yellow (earth) |
| Dual Channel Programmer | E | Wiring Centre | 3 | Green/yellow (earth) |
| Circulation Pump | N | Wiring Centre | 2 | Blue (neutral) |
| Room Thermostat | N | Wiring Centre | 2 | Blue (neutral) |
| Dual Channel Programmer | N | Wiring Centre | 2 | Blue (neutral) |
| Wiring Centre | 1 | Dual Channel Programmer | L | Brown (live) |
| Dual Channel Programmer | 4 | Wiring Centre | 4 | Black |
| Wiring Centre | 4 | Room Thermostat | L | Black |
| Room Thermostat | SL | Wiring Centre | 5 | Brown (live) |
| Dual Channel Programmer | 3 | Wiring Centre | 6 | Grey |
| Cylinder Thermostat | C | Wiring Centre | 6 | Grey |
| Dual Channel Programmer | 1 | Wiring Centre | 7 | Grey |
| Cylinder Thermostat | 1 | Wiring Centre | 8 | Brown (live) |
| Heat-Only Boiler | L | Wiring Centre | 1 | Brown (live) |
| Heat-Only Boiler | N | Wiring Centre | 2 | Blue (neutral) |
| Heat-Only Boiler | E | Wiring Centre | 3 | Green/yellow (earth) |
| Wiring Centre | 8 | Heat-Only Boiler | SL | Orange |
| Heat-Only Boiler | PL | Circulation Pump | L | Brown (live) |
| 3-Port Valve | E | Wiring Centre | 3 | Green/yellow (earth) |
| 3-Port Valve | N | Wiring Centre | 2 | Blue (neutral) |
| 3-Port Valve | W | Wiring Centre | 5 | White |
| 3-Port Valve | G | Wiring Centre | 7 | Grey |
| 3-Port Valve | O | Wiring Centre | 8 | Orange |
| Cylinder Thermostat | 2 | Wiring Centre | 7 | Grey |
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) | Valve rests at B (hot water port); boiler off |
| Hot water only: programmer hot water on (room stat calling, cylinder cold) | Valve stays at B (hot water port); boiler fires |
| Heating only, hot water timed off: programmer heating on (room stat calling, cylinder cold) | Valve drives to A (heating port); boiler fires |
| Heating and hot water: programmer both on (room stat calling, cylinder cold) | Valve at mid position; boiler fires |
| Heating and hot water, the cylinder now hot (room stat calling) | Valve moves to A (heating port); boiler fires |
Where it connects
Lessons that start from it
- The Draw Warm Method: Y-Plan
Foundation · Unit 6
- Quick Jobs
Quick Jobs
- Fault Vault jobs: Y-Plan
Fault Vault jobs: Y-Plan
- Testing
Foundation · Unit 7
- Swapping controls
Intermediate · Unit 2
- Actuator anatomy
Intermediate · Unit 8
Other systems
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.
Read the explanation
- Y-Plan explained: what white, grey and orange do on a mid-position valve
A Y-Plan’s mid-position valve: white calls for heating, grey says hot water is not wanted, orange fires the boiler. None of its cores is a permanent live.
Practise it in the simulator.
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