Connection
Wiring Centre
In short
Wiring Centre: 12-terminal junction box for S-Plan heating systems. It has 12 terminals: 1 (Terminal 1), 2 (Terminal 2), 3 (Terminal 3), 4 (Terminal 4), 5 (Terminal 5), 6 (Terminal 6), 7 (Terminal 7), 8 (Terminal 8), 9 (Terminal 9), 10 (Terminal 10), 11 (Terminal 11), 12 (Terminal 12).
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.
Terminals
| Terminal | What it is | On an S-Plan | On a Y-Plan |
|---|---|---|---|
| 1 | Terminal 1 | Permanent live: fused spur L in; programmer L, boiler L and both valve greys out | Permanent live: fused spur L in; programmer L and boiler L out |
| 2 | Terminal 2 | Neutral: fused spur N in; programmer, boiler, room thermostat, both valves and pump N out | Neutral: fused spur N in; programmer, boiler, valve, room thermostat and pump N out |
| 3 | Terminal 3 | Earth: fused spur E in; programmer, boiler, both valves and pump E out | Earth: fused spur E in; programmer, boiler, valve and pump E out |
| 4 | Terminal 4 | CH demand: programmer terminal 4 (CH ON) in; room thermostat L out | CH demand: programmer terminal 4 (CH ON) in; room thermostat L out |
| 5 | Terminal 5 | CH call: room thermostat SL in; heating valve brown out | CH call: room thermostat SL in; valve white out |
| 6 | Terminal 6 | HW demand: programmer terminal 3 (HW ON) in; cylinder thermostat C out | HW demand: programmer terminal 3 (HW ON) in; cylinder thermostat C out |
| 7 | Terminal 7 | — | Grey: programmer terminal 1 (HW OFF) and cylinder thermostat terminal 2 (satisfied) in; valve grey out |
| 8 | Terminal 8 | HW call: cylinder thermostat terminal 1 (calling) in; hot water valve brown out | HW call: cylinder thermostat terminal 1 (calling) and valve orange in; boiler SL out |
| 9 | Terminal 9 | — | — |
| 10 | Terminal 10 | Switched live: both valve oranges in; boiler SL out | — |
| 11 | Terminal 11 | — | — |
| 12 | Terminal 12 | — | — |
How it fails
- Hot water valve brown landed on the wrong terminal
The valve's brown is landed on an empty terminal, one along from where the cylinder stat's call arrives.
- Supply live open circuit between spur and wiring centre
230 V leaves the spur but never arrives at the other end of the conductor: open circuit.
- Boiler switched live open circuit
Both zones make the switched live at the wiring centre, but it never reaches the boiler's SL: broken conductor.
- Intermittent break in the boiler switched live
The demand is steady at the wiring centre but flickers at the boiler's SL: a conductor breaking down intermittently.
- Boiler switched live landed on permanent live
The boiler's SL is landed on the permanent-live terminal, so it fires with no demand at all - no boiler interlock.
- Boiler live and neutral reversed
L-N 230 V, L-E 0 V, N-E 230 V: reversed polarity at the boiler. It will not run until L and N are the right way round.
Where it connects
Lessons that use it
- The Wiring Centre
Electrical Fundamentals
- Introduction to S-Plan Systems
S-Plan Wiring
- Introduction to Y-Plan Systems
Y-Plan Wiring
- No Power to System
Fault Diagnosis
- Heating Not Working
Fault Diagnosis
- Hot Water Not Working
Fault Diagnosis
- Valve Stuck
Fault Diagnosis
- Intermittent Fault
Fault Diagnosis
Systems it is part of
Also in connection
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