Lennox E206

What does Lennox E206 mean?

E206 flags a failure of the second-stage gas valve relay on the IFC board. When the board cannot switch to high-fire operation, it logs E206 and continues running on first-stage gas only for the remainder of the heating demand. The alert clears after the heat call ends and recovers on the next call. If the unit cannot reach second stage across multiple calls, the IFC board requires replacement.

Symptoms

• E206 alert displayed; furnace continues to run but only in low-fire first-stage mode.
• Home heats slowly during very cold conditions because high-fire capacity is unavailable.
• Thermostat run time increases significantly before the setpoint is reached.
• Alert may occur on every heating cycle or intermittently depending on relay condition.

Common causes

• Failed second-stage relay contact inside the IFC board — open contact prevents high-fire energization.
• Wiring fault on the second-stage gas valve solenoid wiring preventing relay from completing the circuit.
• Control board end-of-life relay failure after extended service hours.
• Voltage surge event damaging the second-stage relay on the board.

Diagnostic steps

1. 01

   Confirm the furnace is running first-stage heat

   Listen for burner operation — with E206 active the unit runs on low fire only. Verify the heat output at supply registers is warm but below normal peak output, consistent with single-stage operation.

2. 02

   Inspect second-stage gas valve wiring

   Check the wiring from the IFC board to the W2 terminal on the gas valve. Verify the wire is connected, the spade terminal is seated, and no open circuit exists in the second-stage solenoid lead.

3. 03

   Measure voltage at the second-stage gas valve terminal

   With the furnace running in heating mode, measure voltage at the second-stage solenoid terminal. If the board is not delivering 24V on a second-stage demand, the relay contact is open and board replacement is required.

4. 04

   Replace the IFC board

   Install the Lennox-specified replacement IFC, re-enter all configuration and capacity code parameters, and verify both first-stage and second-stage gas valve energization on the next heating call.

5. 05

   Confirm two-stage operation after repair

   On a cold-ambient call for heat, verify the furnace transitions to second-stage and that E206 does not return. Check temperature rise in both stages against the SL280DFNV nameplate limits.

When to call a professional

If E206 appears on a recently installed board, there may be a wiring error or configuration issue rather than a failed relay. A licensed technician can perform relay circuit voltage testing to distinguish a board fault from a wiring fault and program the replacement board correctly in the communicating system.