Lennox furnace E110: Low line voltage
E110 means the incoming line voltage is below the furnace's nameplate rating. Lennox's action is to check and correct the supply; the alarm clears five seconds after the voltage recovers.
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
This furnace measures its own supply voltage and reports on it, which most furnace controls do not. E110 says the line voltage is lower than the nameplate rating on the unit. Low voltage matters because motors draw more current to do the same work as voltage falls, so a furnace running on a sagging supply runs hotter and wears faster — the inducer and the blower motor most of all. The alarm clears five seconds after the fault recovers, which means an intermittent E110 in the code history points at something that comes and goes rather than a permanently undersized supply.
Most common causes
- A utility supply genuinely running low, which affects the whole house rather than the furnace alone.
- An undersized or long branch circuit feeding the furnace.
- A loose or corroded connection at the disconnect, breaker, or in the furnace junction box.
- A large load elsewhere in the house pulling the voltage down when it starts.
- A failing breaker or disconnect switch.
How to diagnose it
- Note whether lights elsewhere in the house dim, particularly when a large appliance starts.
- Note whether the code appears at particular times of day, which points at load rather than wiring.
- Note whether other equipment in the house has been behaving oddly.
- Voltage measurement at the furnace is technician work — it means opening a live cabinet.
How to fix it
- If the whole house is affected, this is the utility's problem before it is the furnace's.
- If only the furnace circuit is affected, the branch circuit, its connections and the disconnect need checking by an electrician or HVAC technician.
- The furnace resumes normal operation five seconds after the supply recovers, so nothing needs resetting.
- Do not ignore a recurring E110. Running motors on low voltage shortens their life measurably.
Notes
E110 and E113 are the two ends of the same measurement. Between them the furnace is effectively acting as a supply-voltage monitor, which is genuinely useful information that most furnaces do not provide.
Related
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.