Single-stage furnace ignition retries and watchguard

What happens, in order

1. Gas valve opens and the 4 second trial for ignition runs
2. If flame is not proven in 4 seconds, the gas valve closes and the control does an inter-purge and ignitor warm-up of 35 seconds before the next try
3. The control makes up to five trials in total, including the first
4. After five failed trials the control goes into watchguard flame failure mode and shuts the gas valve
5. After a 60 minute reset period the control starts the ignition sequence again from the beginning
6. Flame lost after being proven during a call counts as a recycle; too many recycles also put the control in watchguard
7. Low flame signal is flagged separately (EL195 flash 4) when the sensor current is weak

Timings and thresholds

Codes you may see during this

EL195 flashes: 3 burner failed to light or lost flame; 4 low flame signal; 5 watchguard, retries or recycles exceeded. ML180: E270, E271, E272, E273, E274, E275

Models

More Lennox furnace sequences

• Two-stage furnace ignition retries and watchguard · Ignition
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• Cooling call on single-stage furnace blower · Cooling
• Two-stage variable speed cooling call · Cooling
• Continuous fan with heat or cool calls · Standby/shutdown