Lennox E225 Error Code

What does Lennox E225 mean?

E225 means the high-pressure switch failed to close during a heating call. On two-stage SL280DFNV models, the high-pressure switch confirms the inducer is producing high-fire draft levels before allowing second-stage operation. When the switch does not close within the allowed time, the board logs E225 and prevents second-stage ignition. Causes are similar to E223 but specifically affect the high-pressure switch circuit.

Symptoms

• Furnace may operate on first stage but fails to transition to second-stage ignition.
• E225 alert displayed on thermostat or control board.
• High-pressure switch reads open with the inducer running at high speed.
• Alert may occur only in cold weather when second-stage heat demand is frequent.

Common causes

• Blocked exhaust vent reducing inducer draft below the high-pressure switch closing setpoint.
• Blocked cold-end heater box or condensate drain restricting airflow through the heat exchanger.
• Weak combustion air inducer motor unable to reach the draft level required for the high-pressure switch to close.
• Kinked or disconnected high-pressure switch hose preventing pressure transmission to the switch.
• Failed high-pressure switch that will not close at the correct draft level.

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Diagnostic steps

1. Inspect vent system for restriction

   Check exhaust and intake vent pipes for blockages, ice, or collapsed sections. Verify proper pipe sizing and total equivalent length does not exceed the SL280DFNV IOM limits.

2. Check condensate drain and cold-end heater box

   Clear any blockage in the condensate trap and drain. Inspect the cold-end heater box for ice or debris accumulation that restricts draft through the secondary heat exchanger.

3. Inspect high-pressure switch hose

   Check the hose connected to the high-pressure switch port for kinks, cracks, or disconnection. Clear any trapped water and verify the hose is fully seated at both ends.

4. Measure inducer draft at high-fire speed

   Using a manometer, measure draft pressure at the inducer housing tap with the inducer running at high speed. Compare against the high-pressure switch closing setpoint in the IOM.

5. Test and replace the high-pressure switch if faulty

   Apply the rated closing pressure to the switch using a manometer and verify continuity. Replace the switch with the Lennox OEM part if it does not close at the specified pressure.

When to call a professional

If draft pressure at high speed is below spec with a clear vent system, the inducer motor is degrading. Measuring inducer motor current draw and comparing it against the nameplate rating requires a clamp meter and knowledge of the rated parameters — a licensed technician can accurately diagnose motor condition and confirm whether inducer replacement is warranted.