Ignition failure - Lockout 109 / Hold 110

What is going on

Burner goes through its ignition trials without proving flame.

Likely causes

• Spark cable off the spark generator or igniter, or green ground wire off the 1/4 in tab
• Blocked exhaust, air inlet, blower, gas valve venturi or heat exchanger
• Manual gas valve closed or low gas line pressure
• Flame rod signal wire disconnected
• No 120 VAC reaching the spark generator
• Spark generator dead
• No 24 VAC reaching the gas valve during trial for ignition
• Gas valve not opening

Check in this order

1. Make sure the high-voltage spark cable is tight at the generator and the igniter electrode, and the green ground wire is on the 1/4 in quick-connect tab
2. Check exhaust, air inlet, blower, venturi and heat exchanger for blockage
3. Open the manual gas valve and verify line pressure against the gas valve section
4. Confirm the flame rod signal wire is seated at the rod and at the control
5. During trial for ignition measure 120 VAC between J5-6 and ground on the control
6. Watch for an arc through the observation port next to the spark electrode in the burner door; with 120 VAC present and no arc, replace the spark generator
7. During trial for ignition measure 24 VAC between J5-2 and J4-10; replace the control if absent
8. Listen for the gas valve click on and off; if the control supplies 24 VAC and wiring is good, test whether the valve responds

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