Connectors
Wiring Centre
In short
A wiring centre is the box where the wires of a heating system meet and are joined. Its terminals: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. The parts list also has it as Compact Wiring Centre.
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.
What it is
A WIRING CENTRE is the box where the wires of a heating system meet and are joined.
This one has twelve numbered BLOCKS. Each block is a plain conductor: every wire landed on a block is joined to every other wire on that block. No block is joined to any other.
The numbers are a habit that helps, not a rule the box knows.
Terminals
| Terminal | What it is for | On the S-Plan example | On the Y-Plan example | On the Combi example |
|---|---|---|---|---|
| 1 | Block 1. | Fused Spur L, Heat-Only Boiler L, 2-Port Valve (heating) G, 2-Port Valve (hot water) G, Dual Channel Programmer L | Fused Spur L, Dual Channel Programmer L, Heat-Only Boiler L | 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 | Block 2. | Fused Spur N, Circulation Pump N, 2-Port Valve (heating) N, Heat-Only Boiler N, Room Thermostat N, 2-Port Valve (hot water) N, Dual Channel Programmer N | Fused Spur N, Circulation Pump N, Room Thermostat N, Dual Channel Programmer N, Heat-Only Boiler N, 3-Port Valve N | 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 | Block 3. | 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 | Fused Spur E, Circulation Pump E, Dual Channel Programmer E, Heat-Only Boiler E, 3-Port Valve E | DrawWarm Combi OUT_E, 2-Port Valve (heating) E, 2-Port Valve (second heating zone) E |
| 4 | Block 4. | Room Thermostat L, Dual Channel Programmer 4 | Dual Channel Programmer 4, Room Thermostat L | — |
| 5 | Block 5. | Room Thermostat SL, 2-Port Valve (heating) B | Room Thermostat SL, 3-Port Valve W | Room Thermostat #1 SL, 2-Port Valve (heating) B |
| 6 | Block 6. | Cylinder Thermostat C, Dual Channel Programmer 3 | Dual Channel Programmer 3, Cylinder Thermostat C | — |
| 7 | Block 7. | — | Dual Channel Programmer 1, 3-Port Valve G, Cylinder Thermostat 2 | — |
| 8 | Block 8. | Cylinder Thermostat 1, 2-Port Valve (hot water) B | Cylinder Thermostat 1, Heat-Only Boiler SL, 3-Port Valve O | — |
| 9 | Block 9. | — | — | Room Thermostat #2 SL, 2-Port Valve (second heating zone) B |
| 10 | Block 10. | 2-Port Valve (heating) O, 2-Port Valve (hot water) O, Heat-Only Boiler SL | — | DrawWarm Combi RT, 2-Port Valve (heating) O, 2-Port Valve (second heating zone) O |
| 11 | Block 11. | — | — | — |
| 12 | Block 12. | — | — | — |
Read from the wired example circuits: S-Plan, Y-Plan, Combi boiler with two heating zones. A wiring-centre block carries whatever is landed on it; the numbers are the habit the lessons teach.
What the meter reads
The Draw Warm Method numbers the blocks:
- 1: the live (L).
- 2: the neutral (N).
- 3: the earth (E).
- 4: the central heating (CH) demand, to the room thermostat (stat).
- 5: the call of the room thermostat.
- 6: the hot water (HW) demand, to the cylinder thermostat.
- 7: the Y-Plan's grey.
- 8: the call of the cylinder thermostat. A Y-Plan's orange is on 8 too.
- 10: the S-Plan's oranges, to the boiler's switched live (SL).
DrawWarm's lessons use block 9 for a second heating zone's call.
The numbering is a habit: read the schedule, never assume.
Call-outs with this part on the path
- No hot water: heating fine, cylinder cold
“Heating's lovely and warm but there's no hot water - the cylinder's cold.”
- Everything dead: no heating, no hot water, the controls dark
“Nothing works. No heating, no hot water, and the controls are dead.”
- Boiler will not fire: the controls work, nothing heats
“The programmer's on and I can hear things whirring, but the boiler never fires - no heating and no hot water.”
- Radiators hot with everything off at the timer
“The radiators get warm when nothing's asking for heat - it's all off at the timer and they're still hot.”
- Boiler fires with everything off, radiators cold
“The boiler keeps firing with everything off at the timer, but the radiators stay cold.”
- Hot water scalding: the cylinder keeps on heating
“The hot water's scalding - far hotter than it used to be, whatever the dial on the cylinder says.”
- Boiler cuts in and out on its own
“It keeps cutting in and out. Works for a bit, the boiler drops off, then it comes back on its own.”
Where it connects
Lessons that use it
- The Manual, History and the examples
Foundation · Using the simulator
- Reading a manufacturer's diagram
Foundation · Reading a circuit
- Cables and terminations
Foundation · Electricity for heating controls
- The CPC and earth continuity
Foundation · Safe isolation and the earth
- The wiring centre and the 3-way connector
Foundation · The parts
- The Draw Warm Method: the parts on the wall
Foundation · The Draw Warm Method: S-Plan
- Block 1: the permanent lives
Foundation · The Draw Warm Method: S-Plan
- The Draw Warm Method: the parts on the wall
Foundation · The Draw Warm Method: Y-Plan
Wiring diagrams it is part of
- 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 two heating zones
Combi
Also in connectors
Read the explanation
- How the wiring centre’s numbered blocks tell the story of an S-Plan
An S-Plan wired in the order it works: the supply on blocks 1 to 3, heating on 4 and 5, hot water on 6 and 8, the valves’ orange cores on 10.
Practise it in the simulator.
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