Thermostat shows E12 and reports low battery or backup power fault (for models with battery backup)

Safety first: Turn off power to the HVAC system before removing the thermostat if you will be opening the housing.

• Step 1 – Identify battery compartment: Remove the thermostat from the wall and locate the backup battery compartment if your iComfort model uses one.
• Step 2 – Replace batteries: Install new, high‑quality batteries of the specified type (often AA or coin cell). Observe correct polarity.
• Step 3 – Clean contacts: If there is corrosion on the contacts, gently clean with a cotton swab and a small amount of isopropyl alcohol. Allow to dry completely before installing new batteries.
• Step 4 – Reinstall and test: Reattach the thermostat to the wall plate and restore power. Confirm that E12 clears.
• Step 5 – Board fault: If new batteries do not clear E12, the charging/monitoring circuit on the main board may be defective. In that case, the thermostat assembly should be replaced.