Furnace control indicates gas valve fault; no gas flow to burners during ignition sequence.

Critical safety: Working on gas valves involves explosion and fire risk. If you smell gas, evacuate and contact your gas supplier or emergency services.

Steps:

• Verify that the external manual gas shutoff to the furnace is fully open (handle parallel to the pipe).
• Inspect the CTC gas valve wiring harness for loose or damaged connectors.
• With power OFF, check for continuity across the gas valve coil terminals. An open reading suggests a failed valve.
• Restore power and call for heat. A trained person can verify that the control board is sending the correct voltage to the gas valve during ignition.
• If the board sends voltage but the valve does not open, replace the gas valve with the exact CTC-specified replacement, following all gas code requirements and leak testing with approved leak detection solution.

Recommendation: Gas valve replacement should be performed and leak-tested by a licensed gas technician.