Thermostat displays 'Low Batt', battery icon flashing, or intermittently powers off; heating becomes unresponsive.

Safety first: This work is low‑voltage and safe for homeowners. Do not attempt to open any mains‑powered receiver or boiler casing.

• Replace batteries: Remove the thermostat from its wall plate or open the battery compartment. Replace all batteries with a full set of new, high‑quality alkaline cells of the correct type (usually AA). Do not mix old and new batteries.
• Clean contacts: Inspect the battery terminals for corrosion or dirt. If present, gently clean with a dry cloth or a cotton bud lightly moistened with isopropyl alcohol. Allow to dry fully before inserting batteries.
• Check orientation: Ensure batteries are inserted with correct polarity (+/−) as marked in the compartment.
• Re-seat thermostat: Clip the thermostat firmly back onto its wall plate or stand to ensure good contact with any low‑voltage pins.
• Test operation: Confirm the display is stable and that the thermostat can call for heat (heating indicator appears and boiler responds).