Error code 12 and furnace starts but shuts down with inducer and blower running, no flame established

Safety: Turn off power and gas before servicing. Gas ignition failures can be hazardous.

Error 12 indicates the control did not detect flame after opening the gas valve.

• Check hot surface igniter:
  • Observe through the sight glass during a call for heat; the igniter should glow bright orange.
  • If it does not glow, test for 120VAC at the igniter leads during ignition. If voltage is present but no glow, replace the igniter.
• Verify gas supply:
  • Ensure the manual gas shutoff is open.
  • If other gas appliances are out, contact the gas utility.
• Check gas valve operation:
  • Listen for a click from the gas valve when ignition should occur.
  • Have a technician measure gas valve voltage and manifold pressure; do not attempt to adjust gas pressure yourself.
• If you smell gas or suspect a leak, shut off gas immediately and call a professional.