Heating System Wiring Diagrams

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

Component Info

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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  ·  V2043H ZONE VALVES  ·  HONEYWELL / RESIDEO

Component Info

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for terminal connections

V2043H Wire Colours

Blue — Neutral → T1
Brown — Permanent Live → T2
Grn/Yel — Earth → T5
Orange — Motor live (zone demand)
White — End-switch OUTPUT ⚡
End-switch closes when valve fully open → fires boiler & pump.
Both valve whites wire in parallel → T8 pump + T9 boiler SW-L.

How S-Plan Works

  1. Programmer CH ON → T3 → Room Stat → T4 → CH valve orange opens valve
  2. CH valve fully open → white end-switch → T8 pump + T9 boiler fire
  3. Programmer HW ON → T6 → Cyl Stat → T7 → HW valve orange opens valve
  4. HW valve fully open → white end-switch → T8 pump + T9 boiler fire
  5. Stat satisfied → spring closes valve → end-switch opens → boiler off
⚠️ White wire is LIVE when valve open. Always isolate before working.
📌 Both zones fully independent. Pump runs whenever either zone calls.
⚠️ 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 Call1 — this is normal.
  3. If cylinder is cold and T7 reads 230V but T9 reads 0V: cyl stat wiring fault — check C → Call1 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→Call1 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 — V2043H

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.
🔌 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 OUT) T1 (N) CH demand + room stat calling ~230V AC 0V = room stat open / wiring break T3→stat→T4
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 OUT) T1 (N) HW demand + cyl stat calling (cold) ~230V AC 0V = cyl stat satisfied (normal when hot) or stat wiring open
T8 (PUMP) T1 (N) Either zone valve fully open ~230V AC 0V = no valve fully open / both end-switches open
T9 (BOILER SW-L) T1 (N) Either zone valve fully open ~230V AC 0V = no valve end-switch closed — boiler will not fire
🌡️ 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 and CH signal reaching CH zone valve orange wire.
  3. CH valve motor energises on orange wire, drives valve open (allow 2–3 minutes). Listen for relay click when fully open.
  4. Probe T8 = ~230V confirms CH valve white end-switch has closed — pump now running.
  5. Probe T9 = ~230V confirms boiler switched live active — boiler should fire. Check flow/return getting hot.
🚿 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→Call1 contacts closed). If 0V and cylinder is cold — cyl stat fault or wiring break.
  3. HW zone valve orange wire energised. Valve drives open (2–3 minutes). End-switch closes when fully open.
  4. Probe T8 = ~230V (pump runs). Probe T9 = ~230V (boiler fires). Both valve whites connect in parallel — either valve alone can fire boiler and pump.
  5. Cylinder heats. When cyl stat satisfied (~60°C), T7 drops to 0V — HW valve de-energises, spring closes, end-switch opens — boiler and pump off.
⚠️ S-Plan Common Faults
FaultLikely CauseTest / Fix
🔥 No heating, no HW Spur tripped. Programmer off. Both valve oranges dead. Check T2 = 230V. Check programmer on. Check T4 and T7.
🌡️ No CH, HW OK Room stat open. T3/T4 break. CH valve orange dead. Probe T3 then T4. Bridge room stat temporarily. Check orange at CH valve.
🚿 No HW, CH OK Cyl stat satisfied/faulty. T6/T7 break. HW valve orange dead. Probe T6 then T7. Check cyl stat set 60°C. Bridge C→Call1 to test stat.
⚡ T8/T9 = 0V — pump & boiler not firing Both valve end-switches open. White wires broken. Valve not fully open. Probe T8 at each valve white individually. Replace valve head if motor fails to open.
💧 Pump runs, boiler won't fire T9 not wired. Boiler CH terminal break. Boiler lockout. Probe T9 = 230V. Check boiler CH/timer terminals. Check boiler fault codes.
🔄 CH on all the time Room stat contacts welded. T4 permanently live. Valve orange never off. Disconnect room stat — if CH stops, stat is welded. Replace stat.
🌊 Valve won't close (spring return failed) Spring return mechanism failed. Orange wire permanently live. De-energise orange wire. If valve stays open — replace valve head or full valve.
🔊 Valve hums but won't open Valve head seized. Scale on spindle. Motor capacitor failed. Try manual lever. If seized — replace valve head. Check orange = 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 pin2→pin3 (closes when cold), cyl stat C→Call1 (closes when cold), valve winding continuity (typical 30–80Ω). An open circuit reading on a stat or valve coil means replace the component.