Lennox E206 Error Code — What It Means
The E206 code on a Lennox furnace indicates a gas valve second-stage relay failure. This means the control board is failing to properly energize or switch the circuit that commands the gas valve into second-stage heating. When this fault occurs, the furnace will continue operating on first stage only for the rest of that heating cycle. The code clears after the fault recovers, but if the unit still cannot operate in second stage on subsequent calls, the control board needs replacement.
This is not a pressure switch, flame sensor, or ignitor problem. It is specifically a relay or control circuit fault tied to the second-stage output. Lennox directs technicians to replace the control if second-stage operation cannot be restored after checking wiring and connections.
Common Causes
- Failed control board relay or contact The internal relay or solid-state switch on the furnace control that energizes second-stage heat has failed or become intermittent.
- Loose or corroded gas valve wiring Connections between the control and the gas valve are loose, corroded, or making poor contact, preventing the second-stage signal from reaching the valve.
- Damaged harness or miswired terminals Field wiring to the gas valve is pinched, broken, or incorrectly terminated, blocking the second-stage command.
- Gas valve not responding to second-stage command The valve itself may not be reacting to the control’s second-stage signal, though Lennox’s corrective action still points to control replacement if the fault persists.
- Intermittent control board fault The board may work intermittently, allowing first stage but dropping second stage randomly due to a partial relay failure.
Step-by-Step Fix
- Verify second-stage demand by confirming the thermostat is calling for second-stage heat and the furnace should be staging based on load and runtime.
- Inspect all gas valve wiring and harness connections at both the control board and the valve terminals for looseness, corrosion, damage, or miswiring.
- Check the control board for visible signs of relay failure, burnt traces, or intermittent second-stage output by observing LED diagnostics and board condition.
- Test wiring continuity from the control’s second-stage output terminals to the gas valve to rule out open or high-resistance field wiring.
- Cycle the furnace into a second-stage call and monitor whether the control energizes the valve. If wiring is intact but second stage still fails, prepare to replace the control.
- Replace the furnace control board if second-stage operation cannot be restored after wiring and connection checks. This is Lennox’s published corrective action for persistent E206.
- Power-cycle the furnace after the repair, then run a full heating cycle through both first and second stages to confirm the code does not return.
Parts Often Needed
| Part | Notes |
|---|---|
| Lennox furnace control board | Amazon | Primary replacement per Lennox when E206 persists. Match your model and serial number. |
| Gas valve wiring harness | Amazon | Replace if damaged, corroded, or pinched during diagnosis. |
| Gas valve | Amazon | Evaluate if control and wiring are ruled out, though Lennox’s E206 fix is control replacement. |
When to Call a Pro
Call a licensed HVAC technician if you are not comfortable working with 120 V control circuits, gas valves, or diagnostic procedures. E206 requires verification of thermostat staging logic, inspection of low-voltage and line-voltage wiring, and correct identification of whether the fault lies in the control or the valve. Control board replacement involves shutting off power and gas, disconnecting multiple wiring harnesses, and confirming proper operation across both heating stages. A qualified technician has the tools and training to safely diagnose relay failures, test wiring continuity, and replace the control without creating new faults or safety hazards.