Lennox EL296UHV Error Code E 204: Gas Valve Mis-Wired
What Does Code E 204 Mean?
The Lennox EL296UHV uses a two-stage gas valve, which has more control connections than a single-stage valve because the SureLight control has to command both a low and a high firing rate. Error E204 means the control's pre-ignition check of the gas-valve circuit found wiring that does not match the expected configuration.
This is a high-severity, safety-related fault. Incorrectly wired gas-valve connections can make the valve behave unpredictably — potentially opening when it should stay closed, or failing to open on command. On a two-stage valve, a wiring error can also cross the first- and second-stage control lines, so the furnace cannot stage correctly even if it lights.
E204 almost always follows service work: a gas-valve replacement, a control-board swap, or any repair where the valve harness was disturbed and reconnected wrong. It is a wiring condition, not a failed valve body, and the code clears once the wiring is corrected.
E204 belongs to a group of gas-valve control faults on this board. It relates to E205, a shorted gas-valve relay contact on the control, and E206, a failed second-stage gas-valve relay. Where those two point to the control's internal relays, E204 points to the external wiring between the control and the valve.
What You'll Notice
- The seven-segment display shows E 204
- The furnace will not light, or refuses to complete its ignition sequence
- The code appeared right after a gas-valve or control-board replacement
- Any gas smell near the furnace (leave immediately and call your gas company)
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Incorrect gas valve wiring connections | Most common | ✗ Call a pro → |
How This Is Diagnosed
A technician treats E204 as a wiring inspection. They compare the gas-valve connections against the furnace wiring diagram, checking that each first-stage and second-stage lead lands on the correct terminal and that no connectors were reversed during prior service.
Once the mis-wired connections are corrected to match the diagram, the technician re-runs the control's checks. The code clears when the wiring matches the expected configuration, and the furnace is only returned to service after the gas-valve circuit is verified correct.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The furnace was recently serviced and E204 appeared afterward
- The gas valve or control board was replaced before the code showed up
- The furnace will not light or complete ignition
- You smell gas near the furnace at any time
Frequently Asked Questions
Is E204 dangerous?
It is treated as a safety issue. Mis-wired gas-valve connections can let the valve act unpredictably, so the furnace should not be run until a technician inspects and corrects the wiring.
Why did E204 appear right after a repair?
The control checks the gas-valve wiring against an expected pattern before ignition. If a harness was reconnected incorrectly during a valve or board replacement, that check fails and E204 is logged.
Does E204 mean the gas valve is bad?
Not usually. The code points to how the valve is wired, not the valve body itself. Correcting the connections to match the wiring diagram typically clears it.
✓ Verified against manufacturer service manual — March 2026