Heating System Wiring Diagrams

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⚡ Fault Finding & Multimeter Tests
Y-PLAN · V4073A · HONEYWELL / RESIDEO

Component Info

Click any component for terminal connections

V4073A Wire Colours

Brown — Perm Live → valve motor (T2)
Blue — Neutral (T1)
Grn/Yel — Earth (T5)
White — Htg ON · CH demand input (T4)
Grey — HW OFF · hold input (T6)
Orange — ⚡ SW-Live OUTPUT → boiler/pump (T9)
Valve States — White / Grey / Orange
0v
0v
230v
HW Only — spring to port B
230v
0v
230v
HW+CH — mid pos, A+B open
230v
230v
230v
CH Only — port A fully open
0v
230v
0v
All off — grey holds position
Source: Resideo 95C-10820-06 & Wiring Guide Issue 19

How It Works

  1. HW demand: Prog HW ON → T7 → Cyl Stat C → (cold) → Call1 → valve HW circuit
  2. CH demand: Prog HTG → T3 → Room Stat 2 → (cold) → pin 3 → T4 → Valve White
  3. Hold: Prog HW OFF → T6 → Valve Grey (holds position)
  4. Fire: Valve Orange OUT → T9 → Boiler SW-L + Pump live
  5. Satisfied: Cyl Stat C+2 → T8 breaks HW demand when hot
⚠️ Isolate 230V before wiring. Orange = LIVE OUTPUT from valve — not an input.
📌 Resideo 95C-10820-06: Orange = boiler & pump live output.
S-PLAN  ·  V4043H ZONE VALVES  ·  HONEYWELL / RESIDEO

Component Info

Click any component
for terminal connections

V4043H Wire Colours

Blue — Neutral → T1
Grn/Yel — Earth → T5
Grey — Permanent Live → T2
Brown — Motor live IN (zone demand)
Orange — End-switch OUTPUT ⚡ → T8 + T9
Brown energises the valve motor when its zone calls for heat. Once the valve is fully open, the internal end-switch closes and Orange becomes live — firing the boiler and pump.

Both valves' oranges wire in parallel to T8 (pump) and T9 (boiler SW-L).
Source: Resideo Heating Controls Wiring Guide Issue 19, p.6 & Motorised Valve Interchangeability Guide p.21

How S-Plan Works

  1. CH demand: Prog CH ON → T3 → Room Stat pin 1 → (cold, 1+3 closed) → pin 3 → T4 → CH valve Brown (motor opens)
  2. HW demand: Prog HW ON → T6 → Cyl Stat C → (cold) → 1 → T7 → HW valve Brown (motor opens)
  3. Perm Live: T2 → Grey on both valves (powers motor coil & end-switch)
  4. Fire: Valve fully open → end-switch closes → Orange OUT → T8 pump + T9 boiler SW-L
  5. Satisfied: Stat opens → brown de-energises → spring closes valve → end-switch opens → boiler off
⚠️ Orange is a LIVE OUTPUT from the end-switch — never an input. Always isolate before working.
📌 Both zones fully independent. Either valve alone can fire boiler & pump via T8/T9.
⚠️ Safety First — Read Before Testing Always use a properly calibrated multimeter rated CAT III 600V or higher. Never probe live terminals with the meter on resistance (Ω) mode. Keep one hand clear of metalwork when probing. If in doubt, isolate and make safe. These tests are for qualified Gas Safe / competent persons only.

Y-Plan — V4073A

MID-POSITION VALVE
Multimeter Setup Set meter to AC Volts — 600V range (or auto-range). Black probe to a known good earth or N (T1). Red probe to the terminal being tested. All readings taken at the wiring centre top or bottom terminals with system calling for heat.
🔌 Wiring Centre — Voltage Tests (Y-Plan)
TerminalBlack probeConditionExpectedIf wrong
T1 (N) Earth / T5 Always ~0–5V AC High V = N/E fault. Call electrician.
T2 (L) T1 (N) Spur ON ~230V AC 0V = spur off / blown fuse / no supply
T3 (HTG) T1 (N) Programmer CH ON, timed period active ~230V AC 0V = programmer fault / CH not timed on
T4 (CH OUT) T1 (N) CH demand + room stat calling ~230V AC 0V = room stat open circuit / stat wiring fault
T5 (E) T1 (N) Always ~0–5V AC High V = earth fault. Isolate immediately.
T6 (HW OFF) T1 (N) Programmer HW OFF output active ~230V AC 0V = programmer HW OFF not wired / programmer fault
T7 (HW ON) T1 (N) Programmer HW ON, timed period active ~230V AC 0V = programmer HW output fault
T8 (CYL SAT) T1 (N) Cylinder cold — stat not satisfied ~230V AC 0V = cyl stat satisfied (normal when hot) or stat wiring open
T9 (SW-LIVE) T1 (N) Valve fully open (CH or HW demand) ~230V AC 0V = valve not fully open / orange end-switch fault
🌡️ Checking Heating is Working — Y-Plan
  1. Set programmer to CH ON. Set room stat above room temperature. Confirm T3 reads ~230V (programmer output live).
  2. Probe T4 — should read ~230V. If 0V, room stat contacts are open: check stat setting, replace stat contacts, or check T3→stat→T4 wiring.
  3. Valve WHITE wire (CH demand) energises. Valve motor drives to mid-position. Allow 2–3 minutes for valve to fully open.
  4. Probe T9 — should read ~230V when valve fully open (orange end-switch closed). If 0V, valve has not reached full open: check valve motor, check white wire from T4 reaching valve.
  5. Boiler and pump should now fire. Confirm flow/return pipes getting hot within 5 minutes.
🚿 Checking Hot Water is Working — Y-Plan
  1. Set programmer to HW ON. Confirm T7 reads ~230V (HW ON output).
  2. Cylinder stat must be calling (cylinder cold). Probe T7 at cyl stat C terminal — should be ~230V. If stat is satisfied (cylinder hot), reading will be 0V at terminal 1 — this is normal.
  3. If cylinder is cold and T7 reads 230V but T9 reads 0V: cyl stat wiring fault — check C → 1 path, check T7 loop through stat back to valve grey/white circuit.
  4. Probe T9 when valve is driven to HW position (spring return, port B open). Should read ~230V from orange end-switch output.
  5. Boiler fires. Cylinder heats. When stat satisfied (typically 60°C), T8 goes live breaking the HW demand — boiler off.
⚠️ Y-Plan Common Faults
FaultLikely CauseTest / Fix
🔥 No heating, no HW No supply. Programmer off. Valve seized. Check T2 = 230V. Check programmer timed on. Try manual override on valve.
🌡️ CH not working, HW OK Room stat open. T3/T4 break. Valve white not energised. Probe T3 then T4. Bridge room stat temporarily to confirm fault location.
🚿 HW not working, CH OK Cyl stat satisfied / faulty. Programmer HW off. T7 break. Probe T7. Check cyl stat set to 60°C. Bridge C→1 on stat to test.
⚡ Boiler won't fire — T9 = 0V Valve not fully open. End-switch failed. Orange wire broken. Listen for valve hum. Check orange wire continuity. Replace valve if motor failed.
🔄 Continuous HW — stat satisfied but boiler stays on Cyl stat contacts welded. T6 (HW OFF) not wired. Grey wire missing from valve. Probe T6 = 230V required. Check grey wire at valve. Replace cyl stat if welded.
💧 Valve jammed / motor hum but no movement Valve head seized. Scale or corrosion on spindle. Manually operate lever on valve head. Replace valve head or full valve body.
🌊 CH on when only HW selected Valve stuck in mid-position. T4 continuously live. Check T4 = 0V when only HW selected. Check room stat wiring. Check valve position.

S-Plan — V4043H

2-PORT ZONE VALVES
Multimeter Setup Set meter to AC Volts — 600V range (or auto-range). Black probe to T1 (neutral) at wiring centre. Red probe to the terminal being tested. System must be calling for heat with programmer and stats set correctly.
📘 V4043H Wire Roles — Per Resideo Issue 19 BLUE = Neutral  ·  G/YELLOW = Earth  ·  GREY = Permanent Live  ·  BROWN = Motor live IN (zone demand)  ·  ORANGE = Switched live OUT (end-switch).
🔌 Wiring Centre — Voltage Tests (S-Plan)
TerminalBlack probeConditionExpectedIf wrong
T1 (N) Earth / T5 Always ~0–5V AC High V = N/E reversal. Isolate immediately.
T2 (L) T1 (N) Spur ON ~230V AC 0V = spur tripped / blown fuse / no supply
T3 (CH PROG) T1 (N) Programmer CH ON, timed period active ~230V AC 0V = programmer CH not outputting / not timed on
T4 (CH MOTOR) T1 (N) CH demand + room stat calling (1+3 closed) ~230V AC 0V = room stat open / wiring break T3→stat→T4. Feeds CH valve BROWN.
T5 (E) T1 (N) Always ~0–5V AC High V = earth fault. Stop work. Isolate.
T6 (HW PROG) T1 (N) Programmer HW ON, timed period active ~230V AC 0V = programmer HW output fault / not timed on
T7 (HW MOTOR) T1 (N) HW demand + cyl stat calling (C+1 closed, cold) ~230V AC 0V = cyl stat satisfied (normal when hot) or stat wiring open. Feeds HW valve BROWN.
T8 (PUMP SW-L) T1 (N) Either zone valve fully open ~230V AC 0V = no valve fully open / no orange end-switch closed.
T9 (BOILER SW-L) T1 (N) Either zone valve fully open ~230V AC 0V = no orange end-switch closed — boiler will not fire.
🔬 At the Valve — V4043H Wire Tests
WireBlack probeConditionExpectedMeaning
Blue Earth / G-Y Always ~0–5V AC Neutral reference
Grey Blue Spur ON ~230V AC (always) 0V = no perm live at T2 / break in grey from T2
Brown Blue This zone calling for heat ~230V AC Motor live IN — valve drives open. 0V = no demand reaching valve.
Orange Blue Valve fully open (after 2–3 min) ~230V AC 0V = end-switch not closed / valve not reached fully open
🌡️ Checking Heating is Working — S-Plan
  1. Set programmer CH ON. Set room stat above room temperature. Probe T3 = ~230V confirms programmer CH output is live.
  2. Probe T4 = ~230V confirms room stat contacts closed (terminals 1+3) and CH demand signal reaching CH zone valve brown wire.
  3. Check CH valve grey = ~230V (perm live always present). Brown energised drives motor open — listen for motor running. Allow 2–3 minutes.
  4. Probe CH valve orange = ~230V confirms end-switch has closed. Same voltage will now appear at T8 and T9.
  5. Probe T8 = ~230V (pump running) and T9 = ~230V (boiler firing). Confirm flow/return pipes getting hot within 5 minutes.
🚿 Checking Hot Water is Working — S-Plan
  1. Set programmer HW ON. Probe T6 = ~230V confirms programmer HW output is live.
  2. Probe T7 = ~230V confirms cyl stat is calling (cylinder cold, C + terminal 1 closed). If 0V and cylinder is cold — cyl stat fault or wiring break.
  3. HW zone valve brown energised. Valve drives open (2–3 minutes). Check grey = ~230V at valve (always present).
  4. HW valve orange = ~230V when fully open — end-switch closed. Both valves' oranges wire in parallel — either alone fires boiler & pump.
  5. Probe T8 = ~230V (pump runs). Probe T9 = ~230V (boiler fires). When cyl stat satisfied (~60°C), C+1 opens — T7 drops to 0V — brown de-energises — spring closes valve — orange drops to 0V — boiler off.
✅ Sanity Check — Back-feed via Orange Per Resideo Issue 19 fault-finding table, when one zone is calling and the other is satisfied: the satisfied valve's orange wire will still show ~230V (back-fed from the active valve's orange via the parallel T8/T9 connection). This is normal and not a fault. The satisfied valve's brown wire will be 0V — that's how you tell which zone is actually driving.
⚠️ S-Plan Common Faults
FaultLikely CauseTest / Fix
🔥 No heating, no HW Spur tripped. Programmer off. No perm live to grey on either valve. Check T2 = 230V. Check programmer on. Check grey = 230V at each valve.
🌡️ No CH, HW OK Room stat open. T3/T4 break. CH valve brown not energising. Probe T3 then T4. Bridge room stat temporarily. Check brown at CH valve = 230V when calling.
🚿 No HW, CH OK Cyl stat satisfied/faulty. T6/T7 break. HW valve brown not energising. Probe T6 then T7. Check cyl stat set 60°C. Bridge C→1 to test stat. Check brown at HW valve.
⚡ T8/T9 = 0V — pump & boiler not firing Neither valve fully open. Orange end-switch not closed. Orange wire broken. Probe orange at each valve. If 0V at valve but brown is live — motor fault or end-switch failed; replace valve head.
💧 Pump runs, boiler won't fire T9 break to boiler. Boiler CH terminal fault. Boiler lockout. Probe T9 = 230V at wiring centre AND at boiler SW-L. Check boiler fault codes.
🔄 CH on all the time Room stat contacts welded. T4 permanently live. Brown never de-energises. Disconnect room stat — if CH stops, stat is welded. Replace stat.
🌊 Valve won't close (spring return failed) Spring return mechanism failed. Brown permanently live (wiring fault). De-energise brown. If valve stays open mechanically — replace valve head.
🔊 Valve hums but won't open Valve head seized. Scale on spindle. Motor capacitor failed. Try manual lever. If seized — replace valve head. Check brown = 230V and grey = 230V at valve.
📋 Pro Tip — Voltage Drop Method To confirm a wire is carrying current (not just showing voltage): probe each end of the wire. A good conductor shows the same voltage at both ends. A voltage drop of more than 5V across a wire indicates high resistance — check terminals, connections, and wire condition.
📡 Continuity Testing (Power OFF) With system fully isolated, use Ω/continuity mode to check: room stat 1→3 (closes when cold, calling), cyl stat C→1 (closes when cold, calling), valve motor winding (typical 30–80Ω between brown and blue at valve). An open circuit reading means replace the component.