Combi · wiring diagram
Combi boiler with two heating zones wiring diagram
In short
A combi boiler heats the radiators and makes hot water at the tap, so there is no cylinder and no hot water valve. From outside it needs a supply, and a switched live for the heating on its room thermostat terminal: from a room thermostat or a wireless receiver’s switch, or, with two heating zones, from the zone valves’ end switches.
DrawWarm's own combi with two heating zones. Each room stat opens its own 2-port valve; both oranges go to block 10 and on to the combi's LR (HTG) terminal. The wiring centre is fed from the boiler's 230 V OUT: one supply for the boiler and its controls. There is no timer on this canvas: an installation needs one too (Boiler Plus), often the boiler's own plug-in clock.
A combi 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 parts
- Wiring Centre
- DrawWarm Combi
Combi Boiler
- Fused Spur
- Room Thermostat
× 2
- 2-Port Valve
× 2
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 | Wired here |
|---|---|
| 1 | Room Thermostat #1 L, DrawWarm Combi OUT_L, 2-Port Valve (heating) G, Room Thermostat #2 L, 2-Port Valve (second heating zone) G |
| 2 | DrawWarm Combi OUT_N, Room Thermostat #1 N, 2-Port Valve (heating) N, Room Thermostat #2 N, 2-Port Valve (second heating zone) N |
| 3 | DrawWarm Combi OUT_E, 2-Port Valve (heating) E, 2-Port Valve (second heating zone) E |
| 5 | Room Thermostat #1 SL, 2-Port Valve (heating) B |
| 9 | Room Thermostat #2 SL, 2-Port Valve (second heating zone) B |
| 10 | DrawWarm Combi RT, 2-Port Valve (heating) O, 2-Port Valve (second heating zone) O |
Every wire, terminal by terminal
| From | Terminal | To | Terminal | Colour |
|---|---|---|---|---|
| DrawWarm Combi | OUT_L | DrawWarm Combi | LR_DHW | Copper link |
| Fused Spur | E | DrawWarm Combi | E | Green/yellow (earth) |
| Fused Spur | N | DrawWarm Combi | N | Blue (neutral) |
| Fused Spur | L | DrawWarm Combi | L | Brown (live) |
| Room Thermostat #1 | L | Wiring Centre | 1 | Brown (live) |
| DrawWarm Combi | OUT_L | Wiring Centre | 1 | Brown (live) |
| DrawWarm Combi | OUT_N | Wiring Centre | 2 | Blue (neutral) |
| DrawWarm Combi | OUT_E | Wiring Centre | 3 | Green/yellow (earth) |
| Room Thermostat #1 | N | Wiring Centre | 2 | Blue (neutral) |
| DrawWarm Combi | RT | Wiring Centre | 10 | Orange |
| Room Thermostat #1 | SL | Wiring Centre | 5 | Brown (live) |
| 2-Port Valve (heating) | E | Wiring Centre | 3 | Green/yellow (earth) |
| 2-Port Valve (heating) | N | Wiring Centre | 2 | Blue (neutral) |
| 2-Port Valve (heating) | B | Wiring Centre | 5 | Brown (live) |
| 2-Port Valve (heating) | G | Wiring Centre | 1 | Grey |
| 2-Port Valve (heating) | O | Wiring Centre | 10 | Orange |
| Room Thermostat #2 | L | Wiring Centre | 1 | Brown (live) |
| Room Thermostat #2 | N | Wiring Centre | 2 | Blue (neutral) |
| Room Thermostat #2 | SL | Wiring Centre | 9 | Brown (live) |
| 2-Port Valve (second heating zone) | B | Wiring Centre | 9 | Brown (live) |
| 2-Port Valve (second heating zone) | O | Wiring Centre | 10 | Orange |
| 2-Port Valve (second heating zone) | G | Wiring Centre | 1 | Grey |
| 2-Port Valve (second heating zone) | N | Wiring Centre | 2 | Blue (neutral) |
| 2-Port Valve (second heating zone) | E | Wiring Centre | 3 | Green/yellow (earth) |
Where it connects
Call-outs on this system
Other systems
- S-Plan
S-Plan
- S-Plan with a digital room stat
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
Back to every wiring diagram.
If this is your home: this page is written for heating engineers, and for learners under the supervision of one. It explains how the wiring works; it is not training to do the work. In England and Wales, electrical work in a home must meet the Building Regulations (Part P), and some of it must be notified to building control or done by a registered electrician; Scotland and Northern Ireland have their own rules. For the wiring, call a registered electrician or a heating engineer competent in controls. Work inside a gas boiler is for a Gas Safe registered engineer only. If you smell gas, leave the building and call the gas emergency number: 0800 111 999 in Great Britain, 0800 002 001 in Northern Ireland.
Practise it in the simulator.
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