E11 appears and the thermostat reports a battery fault even after new batteries are installed; device may shut down unexpectedly.

Safety first: Battery replacement is low risk; ensure correct polarity to avoid damage.

• Use fresh alkaline batteries: Install new, high-quality alkaline AA/AAA batteries as specified by Delta Dore. Avoid mixing old and new cells.
• Clean contacts: Inspect the battery terminals for corrosion or oxidation. Clean gently with a dry cloth or a pencil eraser. Do not use liquids.
• Check spring tension: Ensure the battery springs push firmly against the cells. If a spring is bent or broken, the contact may be intermittent.
• Power cycle: Remove batteries for 2–3 minutes, press any button to discharge residual power, then reinstall batteries and check if E11 clears.

If E11 persists with known-good batteries and clean contacts, the internal voltage sensing circuit is likely faulty and the thermostat should be replaced.