Thermostat shows E16 and battery icon flashes even with new batteries fitted.

Safety first: Battery work is low risk, but avoid shorting cells.

• Use correct batteries: Fit fresh, high-quality alkaline AA/AAA batteries as specified by Drayton. Avoid NiMH rechargeables unless explicitly supported.
• Clean contacts: Remove batteries and clean the contacts with a dry cloth or a cotton bud lightly moistened with isopropyl alcohol. Ensure no rust or white corrosion remains.
• Check spring tension: Gently bend battery springs to improve contact pressure if they appear flattened.
• Test with another set: Try a second set of new batteries to rule out a bad batch.
• Replace thermostat: If E16 persists with good batteries and clean contacts, the internal sensing circuit is likely faulty. Replace the thermostat front module.