Lennox SLP98UHV Error Code E 205: Gas Valve Relay Contact Shorted
What Does Code E 205 Mean?
The E 205 fault on the Lennox SLP98UHV means the gas valve control relay on the SureLight board has shorted, or welded, closed. This relay is the switch the control uses to energize the gas valve; when its contacts fuse together, the board can no longer positively open and close that circuit on command. Because a stuck-closed relay could allow gas to reach the burners at the wrong time, the control locks the furnace out as a safety precaution.
Under normal operation this modulating furnace cycles the gas valve constantly to trim its firing rate, so the board continuously depends on the relay releasing cleanly. When it detects that the relay contact is shorted, it treats the situation as a loss of positive gas control rather than a nuisance and shuts the unit down. This is an internal board failure, not a wiring or setting problem the homeowner can adjust.
E 205 is closely related to E 204 (gas valve mis-wired) in that both are gas-valve control faults, but the cause is different: E 204 is an external wiring error, while E 205 is a failed relay inside the control itself. A shorted relay cannot be field-repaired, so the control board typically needs to be replaced, and the gas valve should be inspected to confirm the relay fault did not damage it.
What You'll Notice
- The furnace has shut down and will not run, displaying E 205
- No heat even though the thermostat is calling
- The burners or gas valve may have behaved abnormally just before the lockout
- The fault returns quickly after power is cycled
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Gas valve relay on control board has welded or stuck closed | Most common | ✗ Call a pro → |
How This Is Diagnosed
A technician confirms the fault points to the board's internal gas valve relay rather than an external wiring problem, distinguishing E 205 from the E 204 mis-wire code. They inspect and test the gas valve control circuit and verify the valve itself operates correctly and shows no signs of damage from the stuck relay.
Because a welded relay contact is inside the sealed control, it cannot be repaired in the field. The technician's remedy is to replace the SureLight control board and then test-fire the furnace to confirm the board commands the gas valve open and closed cleanly.
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:
- This code needs prompt professional attention — the gas valve relay is shorted
- You smell gas near the furnace, or the burners behave abnormally
- The furnace will not operate and displays E 205
- The fault returns immediately after the power is cycled
Frequently Asked Questions
Is E 205 dangerous?
It is treated as a safety fault because a welded gas valve relay could allow gas to flow when it shouldn't. That is exactly why the control locks the furnace out. Leave it off and have a technician replace the affected control board rather than trying to reset around it.
Do I need a whole new control board for E 205?
Usually, yes. The shorted relay is a component inside the sealed SureLight control and cannot be repaired on its own, so the board is replaced as a unit. A technician will also check the gas valve to be sure it wasn't harmed. Exact parts and cost vary by region.
✓ Verified against manufacturer service manual — March 2026