Lennox Error Code E115 indicates Low 24‑V control voltage. Start by checking the most common and safe items identified in the troubleshooting section. If the code returns after those checks, professional diagnosis is recommended.
Easy
Low 24‑V control voltage
Unknown
24‑volt power low (18–30 V) due to inadequate supply or additional power‑robbing equipment
Check and correct control voltage; check for additional power‑robbing equipment; may require larger VA transformer; clears after fault recovered
24‑V power supply, transformer
Call an HVAC technician if the error persists after completing the recommended basic troubleshooting steps or if the system repeatedly locks out.
Disconnect power before inspecting the equipment. Never bypass safety devices or operate the system if you suspect unsafe conditions.
Learn more about the furnace components and operating conditions commonly associated with diagnostic error codes: