Lennox E116 Error Code

What does Lennox E116 mean?

E116 indicates the 24VAC secondary voltage to the indoor unit (furnace or air handler) has risen above the acceptable range of 18–30VAC. The Lennox communicating thermostat displays this code when it detects high secondary voltage at the component. Unlike many alert codes, E116 clears when the control senses proper voltage after checking and correcting line voltage.

Symptoms

• E116 or 'High Secondary (24VAC) Voltage' displayed on the thermostat.
• System may operate intermittently with voltage fluctuations.
• Alert may appear alongside E113 (high line voltage) if the primary cause is utility overvoltage.
• Other 24VAC components on the system may also experience elevated voltage.

Common causes

• Line voltage supplied to the transformer primary is higher than rated, causing proportionally elevated secondary voltage.
• Wrong transformer installed — transformer with a lower primary voltage rating than the actual supply voltage, resulting in higher secondary output.
• Transformer primary taps not matched to actual supply voltage.

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Diagnostic steps

1. Measure line voltage at the equipment

   With the system running, measure voltage at the primary side of the transformer. Compare to nameplate. Elevated primary voltage produces proportionally elevated secondary voltage.

2. Verify transformer primary tap is set correctly

   Some transformers have multiple primary tap terminals (e.g., 208V, 230V, 240V). Confirm the wire is connected to the tap that matches the actual supply voltage.

3. Measure 24VAC secondary voltage

   Measure across the transformer secondary terminals. On a 24VAC system, voltage should be 18–30VAC under load. A reading above 30VAC confirms the secondary is high and the transformer or primary voltage must be corrected.

4. Address primary line voltage if high

   If line voltage is above rating, this is a utility-side issue. Document readings and contact the utility company. Check for an open neutral as described under E113.

When to call a professional

Transformer tap changes and primary voltage corrections should be performed by a licensed HVAC technician or electrician. Sustained overvoltage on the 24VAC circuit can damage communicating control boards, thermostats, and accessory modules — address E116 promptly rather than continuing to operate the system.