Lennox furnace E114: Line voltage frequency out of range
E114 means the control is not seeing 60 hertz power. Lennox's wording is direct: no 60 hertz power. Check voltage and line power frequency, and correct both.
Applies to: Lennox gas furnaces with a seven-segment diagnostic display on the control board, such as the ML193UHEK, per installation instructions 508565-01.
What it means
The control uses the supply frequency as a timing reference, so a supply that is not at 60 hertz makes its internal timing unreliable. On a normal utility connection this code should never appear — grid frequency is held very tightly. When it does appear, the supply is almost always not the utility. A generator running off speed, an inverter producing a poor waveform, or a UPS in a backup mode are the realistic causes, and all three are increasingly common as houses add battery backup.
Most common causes
- A generator running off speed, which is the most common cause.
- An inverter or battery backup producing a modified rather than pure sine wave.
- A UPS or transfer switch feeding the furnace during an outage.
- A genuine utility disturbance, which is rare and usually brief.
- A control misreading the supply, which is the least likely explanation.
How to diagnose it
- Note whether the house was on generator or battery backup when the code appeared. That answers it most of the time.
- Note whether the code coincided with a power outage.
- If the house has recently had a backup system installed, that is the thing to look at.
- Frequency measurement is technician work.
How to fix it
- If a generator is the source, it needs to be governed to the correct speed.
- If an inverter is the source, a furnace with electronic controls needs a pure sine wave output rather than a modified one.
- The furnace resumes normal operation five seconds after the fault recovers.
- A stored E114 with no backup system in the house is worth reporting to the utility.
Notes
This code is a good example of a diagnostic that means nothing on its own and everything in context. The same code is routine on generator power and alarming on utility power.
Related
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.