Lennox EL296UHV Error Code E 117: Poor Ground Detected
What Does Code E 117 Mean?
Code E117 on the Lennox EL296UHV is a warning that the SureLight integrated control sees a degraded earth ground: a ground path that is still present but has higher resistance than it should. Unlike E112, which drops the furnace entirely when no ground is detected, E117 lets the furnace keep operating while flagging that the grounding needs attention. The warning clears roughly 30 seconds after the ground quality improves.
A poor ground usually comes from a loose ground terminal at the furnace, corrosion on the ground conductor or its connection points, or a grounding electrode connection at the panel that has degraded over time. Thermal cycling and vibration slowly work connections loose, so a ground that was solid at installation can drift into the marginal range years later.
Grounding is not just a code-compliance detail on this furnace — the flame-sensing circuit passes its small sensing current to ground, so a marginal ground can eventually show up as unstable flame readings. That makes E117 worth acting on even though nothing has stopped. Think of E117 and E112 as two points on the same scale: E117 is the early warning that the ground is weakening, and E112 is the shutdown that follows if it fails outright. Tightening and verifying ground connections is line-voltage work for an electrician or HVAC technician.
What You'll Notice
- "E 117" appears as a warning while the furnace continues to run
- The ground wire at the furnace looks loose, corroded, or poorly terminated
- The warning comes and goes rather than staying constant
- Occasional flame-sensing or grounding-related quirks accompany the warning
- The furnace still heats, but the code keeps logging
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Loose or corroded ground wire connection | Most common | ✗ Call a pro → |
How This Is Diagnosed
A technician inspects and tightens the ground connections at the furnace, then checks the resistance and continuity of the ground path back toward the panel and its grounding electrode system, looking for the high-resistance point that triggered the warning. Corrosion and loose terminals are the usual findings.
Because the same ground supports flame sensing, the technician typically confirms that the flame signal is steady once the ground is improved. E117 clears on its own about 30 seconds after the connection is restored, so verification is watching the warning stay gone through a normal cycle.
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 E117 warning appears consistently or keeps recurring
- The furnace also logs flame-sensing or polarity codes
- The ground wire or its terminals look corroded or loose
- The warning escalates toward E112 (ground not detected)
Frequently Asked Questions
Can I keep using my furnace with an E117 warning?
The furnace will keep running because E117 is a warning rather than a shutdown, but a weak ground affects both safety and flame sensing, so it should be improved before it degrades further into a hard E112 fault.
Why does grounding matter for a furnace?
Beyond general electrical safety, the flame-sensing circuit on this furnace relies on a clean ground path to carry its small sensing current. A poor ground can eventually make flame detection unreliable, which is why the control bothers to warn about it.
Is fixing the ground a DIY job?
No. Improving the ground means working with line-voltage wiring and verifying the ground path back to the panel, which is best handled by an electrician or HVAC technician.
✓ Verified against manufacturer service manual — March 2026