Thermostat shows E16 and indicates backup battery or supercapacitor fault; time and settings may reset after power loss.

Safety: Turn off power to the thermostat before opening any battery compartment or removing the unit from the wall.

• Step 1 – Locate backup power source: Some Johnson Controls smart thermostats use an internal coin cell battery or supercapacitor. Check the user manual for your model.
• Step 2 – Replace coin cell (if present): Open the battery compartment and replace the coin cell with the exact specified type, observing polarity. Do not use tools that could short the battery.
• Step 3 – Inspect for corrosion: Clean any light corrosion on contacts with a cotton swab and isopropyl alcohol. If heavily corroded, the thermostat may need replacement.
• Step 4 – Power cycle and test: Restore power and verify that time and settings are retained after briefly cutting power again.
• Step 5 – Replace thermostat: If your model uses a supercapacitor or integrated RTC circuit and E16 persists, the component is not field‑replaceable. Replace the thermostat.