Brand: Lennox
Category: Home HVAC System
Manual Type:
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Manual for LF25 - Troubleshooting and error codes + PDF Download
Uploaded: March 30, 2025, 4:26 p.m.
Manual Publish Date: 2019-08-01
Warranty Summary
Warranty information is not mentioned in this installation manual.
Heating Sequence of Operation:
- When thermostat calls for heat, combustion air inducer starts.
- Combustion air pressure switch proves inducer operation.
- After pre-purge (approx. 30 seconds), spark ignition energizes and solenoid valves open.
- Spark ignites gas, ignition sensor proves flame, and combustion continues.
- If flame not detected after 10-second trial, controller repeats ignition sequence twice before lockout (60 minutes).
- Burners must light without crossover delay, flames predominantly blue and centered.
- Fan energizes approximately 30 seconds after ignition.
- When thermostat satisfied, gas valve closes; combustion air inducer shuts off after 30 seconds.
- System fan shuts off approximately 150 seconds after gas valve de-energizes.
Troubleshooting and error codes
Status Table (Responsive)
| LED | UNIT OPERATION |
|---|---|
| Slow Flash* | Normal Operation - No call for heat |
| Fast Flash | Normal Operation - Call for heat |
| 2 Flashes | System lockout - failed to detect or sustain flame |
| 3 Flashes | Pressure switch failed closed before CAI is energized or failed open after CAI is energized |
| 4 Flashes | High limit (S10) switch open |
| 5 Flashes | Flame sensed and gas valve (GV1) not energized |
| 6 Flashes | On-board microprocessor fault. |
| 7 Flashes | Pressure switch (S18) closed with inducer off. |
| 8 Flashes | Rollout switch (S47/S195) open. Cycle-power to reset. |
| Steady On | Control board (A3) failure |
| Steady Off | Internal control board (A3) failure or not power. |
Troubleshooting and error codes
Status Table (Responsive)
| LED | UNIT OPERATION |
|---|---|
| Slow Flash* | Normal Operation - No call for heat |
| Fast Flash | Normal Operation - Call for heat |
| 2 Flashes | System lockout - failed to detect or sustain flame |
| 3 Flashes | Pressure switch failed closed before CAI is energized or failed open after CAI is energized |
| 4 Flashes | High limit (S10) switch open |
| 5 Flashes | Flame sensed and gas valve (GV1) not energized |
| 6 Flashes | On-board microprocessor fault. |
| 7 Flashes | Pressure switch (S18) closed with inducer off. |
| 8 Flashes | Rollout switch (S47/S195) open. Cycle-power to reset. |
| Steady On | Control board (A3) failure |
| Steady Off | Internal control board (A3) failure or not power. |