Lennox SLP98UHV Error Code E 114: Line Voltage Frequency Out-of-Range
What Does Code E 114 Mean?
Error code E114 on the Lennox SLP98UHV means the line voltage frequency is out of range — the control is not seeing the 60 Hz power it expects. In North America the grid runs at 60 Hz, and the SureLight control uses that frequency as a timing reference, so an off-frequency supply trips E114.
The most common scenario is the furnace running on a portable generator that is not producing clean 60 Hz output. Inexpensive or overloaded generators can deliver an unstable frequency the control rejects. An actual utility frequency problem is possible but rare. E114 sits in the power-quality family with E110 (line voltage too low) and E113 (line voltage too high); those two watch voltage magnitude on the 120V line while E114 watches its frequency, and E115 separately watches the 24V transformer secondary.
Because the SLP98UHV's variable-speed motors and communicating electronics depend on stable frequency for correct timing, off-frequency power can make motors run at the wrong speed and throw off control timing. An electrician should check the power quality at the furnace; if it is on generator power, the generator's output and load should be verified.
What You'll Notice
- E 114 shown on the furnace control's 7-segment display
- The furnace will not start or cuts out while the code is present
- The system is currently running on a portable or backup generator
- Motors sound like they are running at the wrong speed or surging
- The code appears during an abnormal utility power event
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Abnormal utility power supply or generator with incorrect frequency | Most common | ✗ Call a pro → |
How This Is Diagnosed
A technician first establishes how the furnace is being powered. If it is on a portable or backup generator, the generator is the prime suspect: its output frequency and loading are checked, since an overloaded or low-quality generator commonly produces off-frequency power that the control rejects.
If the furnace is on normal utility power, an electrician measures the supply frequency with proper instruments to confirm it is genuinely out of range. A true utility frequency fault is rare, so the technician also rules out any inverter, UPS, or other power-conditioning device between the panel and the furnace.
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 power-supply frequency needs to be measured with proper instruments
- The furnace is running on a generator that may not produce clean 60 Hz power
- E114 appears on normal utility power, suggesting a power-quality problem
- An inverter, UPS, or backup power device feeds the furnace
Frequently Asked Questions
I'm running my furnace on a generator during an outage — is that the cause?
Most likely. Portable generators, especially when overloaded or inexpensive, often produce an unstable frequency that the SLP98UHV control will not accept, which triggers E114. Verifying the generator's output and reducing its load is the place to start.
Will E114 clear on its own once normal power returns?
If the off-frequency power was the cause, the code typically clears once the furnace is back on a clean 60 Hz supply. If it persists on normal utility power, the supply should be measured by an electrician.
Can running on bad-frequency power damage the furnace?
Off-frequency power can make the variable-speed motors run at the wrong speed and upset control timing. The control blocks operation with E114 specifically to avoid running the equipment under those conditions.
✓ Verified against manufacturer service manual — March 2026