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S plan and Y plan wiring: a 10-way junction box, terminal by terminal

For a 10-way junction box or wiring centre. Pick the system, then see every wire on each of the 10 terminals: the programmer, room stat, cylinder stat, zone valves, boiler and pump. Tap a part to show only its wires. Built for a phone on site.

Guidance only. This follows Honeywell’s published drawings for its 10-way junction box (sources below). Terminal numbers on other wiring centres, programmers and boilers can differ: always follow the instructions supplied with the parts you are fitting. Isolate and prove dead before you touch anything.

Terminal list (the interactive version needs JavaScript).

S plan: two 2-port zone valves (Honeywell V4043H on the drawing)

  1. 1: Permanent live. Supply (3A rated): L; Programmer: L; Room stat receiver: L; Heating zone valve: Grey; Hot water zone valve: Grey.
  2. 2: Neutral. Supply (3A rated): N; Programmer: N; Room stat receiver: N; Heating zone valve: Blue; Hot water zone valve: Blue; Boiler: N; Pump: N.
  3. 3: Earth. Supply (3A rated): E; Programmer: E; Heating zone valve: Green/yellow; Hot water zone valve: Green/yellow; Boiler: E; Pump: E.
  4. 4: Heating ON (from programmer). Programmer: CH ON (marked 4 on the drawing); Room stat receiver: A (common).
  5. 5: Heating call (from room stat). Room stat receiver: B (call for heat); Heating zone valve: Brown (motor).
  6. 6: Hot water ON (from programmer). Programmer: HW ON (marked 3 on the drawing); Cylinder thermostat: 1.
  7. 7: Not used. Nothing connected.
  8. 8: Hot water call (from cylinder stat). Cylinder thermostat: C; Hot water zone valve: Brown (motor).
  9. 9: Not used (pump overrun boilers use it). Nothing connected.
  10. 10: Boiler and pump switched live. Heating zone valve: Orange (end switch); Hot water zone valve: Orange (end switch); Boiler: L (switched live); Pump: L.

S plan with a pump overrun boiler, these terminals change:

  1. 9: Pump live (pump overrun). Boiler: PL (pump live); Pump: L.
  2. 10: Boiler switched live. Heating zone valve: Orange (end switch); Hot water zone valve: Orange (end switch); Boiler: SL (switched live).

Y plan: one 3-port mid-position valve (Honeywell V4073A on the drawing)

  1. 1: Permanent live. Supply (3A rated): L; Programmer: L; Room stat receiver: L.
  2. 2: Neutral. Supply (3A rated): N; Programmer: N; Room stat receiver: N; 3-port mid-position valve: Blue; Boiler: N; Pump: N.
  3. 3: Earth. Supply (3A rated): E; Programmer: E; 3-port mid-position valve: Green/yellow; Boiler: E; Pump: E.
  4. 4: Heating ON (from programmer). Programmer: CH ON (marked 4 on the drawing); Room stat receiver: A (common).
  5. 5: Heating call (from room stat). Room stat receiver: B (call for heat); 3-port mid-position valve: White.
  6. 6: Hot water ON (from programmer). Programmer: HW ON (marked 3 on the drawing); Cylinder thermostat: C.
  7. 7: Hot water off or satisfied. Programmer: HW OFF (marked 1 on the drawing); Cylinder thermostat: 2; 3-port mid-position valve: Grey.
  8. 8: Boiler and pump switched live. Cylinder thermostat: 1; 3-port mid-position valve: Orange; Boiler: L (switched live); Pump: L.
  9. 9: Not used (pump overrun boilers use it). Nothing connected.
  10. 10: Not used (pump overrun boilers use it). Nothing connected.

Y plan with a pump overrun boiler, these terminals change:

  1. 8: Cylinder stat and valve output. Cylinder thermostat: 1; 3-port mid-position valve: Orange; Link wire: To terminal 10.
  2. 9: Pump live (pump overrun). Boiler: PL (pump live); Pump: L.
  3. 10: Boiler switched live. Link wire: From terminal 8; Boiler: SL (switched live).

Commissioning checks (S plan)

From the checkout procedure in Honeywell’s V4043H instructions, after filling the system and switching on:

  1. Check each valve’s manual lever is in AUTO, the programmer has power, and the boiler is on with its thermostat at maximum.
  2. Hot water: turn the room stat to minimum (or heating off at the programmer). Set the cylinder stat to maximum and the programmer to hot water on. The pump should run and the boiler fire, and the pipe after the hot water valve should get hot.
  3. Heating: turn the cylinder stat to minimum (or hot water off at the programmer). Set the room stat to maximum and the programmer to heating on. The boiler should fire, the pump run, and the pipe after the heating valve get hot.
  4. Set the stats back. Honeywell gives 60 °C for the cylinder stat and 20 °C for the room stat as the normal settings, and the programmer back to the customer’s mode.

Where the drawings come from

  • Honeywell, Lyric T6, T6R and Honeywell T4R: S and Y Plan applications, additional wiring instructions (2016): S plan and Y plan on the 10-way junction box, with the receiver’s L, N, A and B.
  • Honeywell, V4043H Motorised Zone Valve installation instructions, Form 95C-10819-2, Rev. 09/04: S plan wiring, the white-wire note, the single-channel link, and the checkout procedure.

Room stats are shown by job (common and call for heat), and the programmer by channel (CH ON and HW ON), because the terminal numbers on those differ from make to make. Check the backplate labels.

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