Thermostat displays F.15 and time/date keep resetting

Safety: Only low‑voltage handling is required. Do not attempt to replace internal backup cells unless specified by Glow‑worm.

Steps:

• Ensure the thermostat has a stable power supply (fresh batteries or stable mains/24 V feed).
• Set the correct time and date manually, then leave the thermostat powered continuously for at least 24 hours.
• If the thermostat supports automatic time sync via internet, enable NTP or cloud time synchronisation.
• Power‑cycle the thermostat briefly and check whether the time is retained.

Remedy:

• If the time resets after every power interruption and F.15 persists, the internal RTC or backup storage is defective. Replace the thermostat head.
• Where available, update firmware to the latest version before replacement to rule out software issues.