What causes Lennox Gas Furnace E112?

A missing, loose, or broken equipment ground wire between the furnace and the electrical panel (Lennox's only listed fix is to provide proper earth ground). Recent electrical work, a replaced furnace disconnect or receptacle, or a new furnace installed without the ground conductor connected. A loose ground connection at the furnace's junction box or at the panel's ground bar. A wiring fault that also shows up as related line-power codes, such as E 111 (polarity reversed) or E 117 (poor ground).

How do I fix Lennox Gas Furnace E112?

Read the code: look at the seven-segment LED on the furnace control through the sight glass, or check the alert on your Lennox thermostat (alert 112). You can recall the last 10 error codes by holding the diagnostic button until 'E' shows, then releasing it. Think about what changed. If an electrician, installer or handyman just worked on the furnace circuit, the panel, or the furnace switch, call them back first; a disconnected ground is a common leftover. Check the furnace's breaker and service switch are fully on. Don't keep cycling power hoping it clears: E112 is a real wiring condition and Lennox says the system only resumes once the ground is restored. If the furnace is also showing E 111 or E 117 in the code history, mention that to the electrician or technician; it points to the same power wiring. Don't open the furnace junction box or the electrical panel yourself unless you're qualified. Lennox warns the unit must be grounded in accordance with national and local codes and that improper grounding is an electric shock hazard.

When should I call a pro for Lennox Gas Furnace E112?

Any time E112 is active. Restoring the equipment ground is electrical work, and Lennox's instruction is simply to provide proper earth ground. An electrician or HVAC technician will check the ground conductor from the furnace back to the panel and the connections at both ends, and confirm line polarity, since Lennox lists reversed polarity (E 111) as a separate fault on the same control. If the ground and polarity test good and the code persists, the technician will look at the furnace's integrated control. You notice shocks from the furnace cabinet or ductwork, burning smells, or scorched wiring: switch off the furnace breaker and leave it off until it's inspected. You smell gas: leave the house and call your gas utility from outside.

Code: E112🔥 Lennox Gas Furnace

Lennox Furnace Error 112 (E112): Ground Not Detected (Meaning, Causes, Fixes)

Q: What does Lennox Gas Furnace E112 mean?

Error 112 on a Lennox furnace means the control can't find an earth ground on the furnace's power supply, so it shuts the system down. This is an electrical wiring problem, not a furnace part wearing out: the fix is restoring a proper ground to the unit. Lennox says the furnace starts running normally again about five seconds after the ground is restored. Lennox service literature for its communicating SureLight furnaces (SL280UHV, SL280DFNV, EL296UHV and similar) lists E 112 as 'Ground not detected', with the action 'System shuts down. Provide proper earth ground. System resumes normal operation 5 seconds after fault recovered.' On a Lennox smart or iComfort communicating thermostat the same problem shows as alert 112, 'GF No Ground Connection'; Lennox's alert-code guide says the reporting component cannot find earth ground and the thermostat shuts the system down, and that the alert clears automatically once the problem is gone. It sits in a group of line-power checks the control runs: E 110 is low line voltage, E 111 is reversed line polarity, and E 117 is a milder 'Poor ground detected' warning that doesn't stop the furnace. Lennox notes these furnaces contain polarity-sensitive electronics and must be wired correctly and properly grounded.

Reviewed 2026-10-23 · Based on 4 manufacturer & service sources

What the code means

Lennox service literature for its communicating SureLight furnaces (SL280UHV, SL280DFNV, EL296UHV and similar) lists E 112 as 'Ground not detected', with the action 'System shuts down. Provide proper earth ground. System resumes normal operation 5 seconds after fault recovered.' On a Lennox smart or iComfort communicating thermostat the same problem shows as alert 112, 'GF No Ground Connection'; Lennox's alert-code guide says the reporting component cannot find earth ground and the thermostat shuts the system down, and that the alert clears automatically once the problem is gone. It sits in a group of line-power checks the control runs: E 110 is low line voltage, E 111 is reversed line polarity, and E 117 is a milder 'Poor ground detected' warning that doesn't stop the furnace. Lennox notes these furnaces contain polarity-sensitive electronics and must be wired correctly and properly grounded.

Likely causes

A missing, loose, or broken equipment ground wire between the furnace and the electrical panel (Lennox's only listed fix is to provide proper earth ground)
Recent electrical work, a replaced furnace disconnect or receptacle, or a new furnace installed without the ground conductor connected
A loose ground connection at the furnace's junction box or at the panel's ground bar
A wiring fault that also shows up as related line-power codes, such as E 111 (polarity reversed) or E 117 (poor ground)

Safe DIY checks

⚠ Before you start

Turn off power at the furnace/HVAC service switch and the breaker before opening panels. Shut the gas valve before any work near the burners, and never disconnect or alter the gas line. If you smell gas, leave the house and call your gas utility.

Read the code: look at the seven-segment LED on the furnace control through the sight glass, or check the alert on your Lennox thermostat (alert 112). You can recall the last 10 error codes by holding the diagnostic button until 'E' shows, then releasing it.
Think about what changed. If an electrician, installer or handyman just worked on the furnace circuit, the panel, or the furnace switch, call them back first; a disconnected ground is a common leftover.
Check the furnace's breaker and service switch are fully on. Don't keep cycling power hoping it clears: E112 is a real wiring condition and Lennox says the system only resumes once the ground is restored.
If the furnace is also showing E 111 or E 117 in the code history, mention that to the electrician or technician; it points to the same power wiring.
Don't open the furnace junction box or the electrical panel yourself unless you're qualified. Lennox warns the unit must be grounded in accordance with national and local codes and that improper grounding is an electric shock hazard.

🛠 When to call a pro

Any time E112 is active. Restoring the equipment ground is electrical work, and Lennox's instruction is simply to provide proper earth ground.
An electrician or HVAC technician will check the ground conductor from the furnace back to the panel and the connections at both ends, and confirm line polarity, since Lennox lists reversed polarity (E 111) as a separate fault on the same control.
If the ground and polarity test good and the code persists, the technician will look at the furnace's integrated control.
You notice shocks from the furnace cabinet or ductwork, burning smells, or scorched wiring: switch off the furnace breaker and leave it off until it's inspected.
You smell gas: leave the house and call your gas utility from outside.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Non-contact voltage tester

For a safe first check that a circuit is live before anyone works on it; it can't confirm a ground connection.

[affiliate link slot: AFFILIATE_SLOT_VOLTAGE_TESTER]

⚙

Digital multimeter

What a technician uses to check voltage and ground continuity at the furnace.

[affiliate link slot: AFFILIATE_SLOT_MULTIMETER]

⚙

Lennox SureLight integrated control board (exact OEM part number)

Only if a technician confirms the ground and polarity are correct and the control still reports E112.

[affiliate link slot: AFFILIATE_SLOT_BOARD]

Sources

Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.