6.1.1 Single‑Stage Gas Valve (On / Off Only)

A. Coil Resistance Test (Power OFF – Limited Use)

Purpose:
Used only to identify hard electrical coil failures.
This test does not confirm correct gas valve operation.

Assessment

• ✅ True open circuit
  (no continuity in both polarities, valve unplugged)
  → Failed coil

• ✅ Near‑zero Ω (dead short)
  → Failed coil

• ❌ OL or unstable readings in one direction only
  → NOT a valid failure indicator
  (internal rectifiers/diodes may block the meter)

B. Live Voltage & Gas‑Flow Test (PRIMARY TEST)

Purpose:
Confirms the ICS is commanding the valve AND the valve is mechanically opening.

Procedure

1. Restore power
2. Call for heat
3. Measure voltage at:
   • Orange ↔ Black
4. ✅ Expect 24 Vac during ignition sparking

Gas‑Flow Confirmation

• Connect manometer to the operating test point
• Gas must be present within 4 seconds of ignition sparking starting

Decision

• ✅ 24 Vac + gas flow present
  → Valve operating correctly

• ✅ 24 Vac present + NO gas flow (after 4 s)
  → Valve slow opening or sticking → Replace valve

• ❌ No 24 Vac present
  → Fault is not the valve
  (check OT3, safeties, airflow proving, ICS)

6.1.2 Two‑Stage Gas Valve (Low / High Fire)

A. Coil Resistance Test (Power OFF – Limited Use)

Purpose:
Used only to identify hard electrical coil failures on either stage.
Resistance testing alone does not confirm correct staging or operation.

Assessment (Either Coil)

• ✅ True open circuit
  → Failed coil – replace entire valve

• ✅ Near‑zero Ω (dead short)
  → Failed coil – replace entire valve

• ❌ OL or odd readings one way only
  → NOT a valid failure indicator

Wiring Identification

• Black = Common
• Orange = Main ON / OFF (Low fire supply)
• Yellow = High fire stage

B. Live Voltage & Gas‑Flow Test (PRIMARY TEST)

Purpose:
Confirms correct staging command from the ICS and physical valve response.

High‑Fire Operation

• Orange ↔ Black = 24 Vac
• Yellow ↔ Black = 24 Vac

✅ Confirms valve is being commanded to high fire

Low‑Fire Operation

• Orange ↔ Black = 24 Vac
• Yellow ↔ Black = 0 Vac

✅ Confirms valve has dropped to low fire

Gas‑Flow Confirmation (Both Stages)

• Connect manometer to test point
• Gas must be present within 4 seconds of ignition sparking

Decision

• ✅ Correct voltage + gas flow present
  → Valve operating correctly

• ✅ Correct voltage + NO gas flow (after 4 s)
  → Valve slow opening or sticking → Replace valve

• ❌ No 24 Vac to Orange
  → Fault is not the valve
  (check OT3, safeties, airflow proving, ICS)

6.1.3 Modulating Gas Valve (ICS Modulation)

✅ Resistance testing is VALID for modulating gas valves
(Modulating valves use separate, non‑rectified coils)

A. Coil Resistance Test (Power OFF)

Purpose:
Confirms electrical integrity of both coils before live testing.

Setup

• Heater OFF
• 230 Vac isolated
• Gas valve plug disconnected
• Multimeter set to Ω

Expected Readings

Decision

• ✅ Readings within range → Proceed to live signal test
• ❌ Any open circuit, short circuit, or out‑of‑range value → Replace entire gas valve

B. Live Signal Test (Power ON)

Purpose:
Confirms ICS is commanding valve operation and modulation.

Procedure

1. Restore power
2. Call for heat
3. Measure signals at the gas valve with plug connected

Expected Signals

• On/Off coil (Black ↔ Orange):
  ✅ >9 Vac when valve is commanded ON

• Modulating signal (Blue ↔ Purple):
  ✅ 5–17 Vdc, varying with heat demand

Decision

• ✅ Correct voltage present and modulation active → Valve operating normally
• ✅ Correct voltage present but no modulation or gas response → Valve fault → Replace valve
• ❌ No control voltage present → ICS or wiring fault (do not replace valve) - Check OT3, safeties, airflow proving, ICS)