Replaces Honeywell ST9100C, ST9100A, and ST6100: Designed to replace these Honeywell timers. Clips onto the same 6-terminal Honeywell backplate. No rewiring needed in compatible systems. 3 On/Off periods with flexible scheduling: Program up to three heating cycles per day. Choose from 24-hour, 5/2-day or full 7-day schedules. Ideal for combi boilers and single heating zones. Boost, Override and Holiday Modes: Boost adds up to 3 hours of heat. Holiday Mode pauses heating for up to 99 days. Manual Override lets you switch heating on/off until next event. Backlit LCD screen with clear prompts: Text-based display shows current status, next event and menu guidance. Simple layout makes setup quick and easy for any user. No batteries required – memory is built in: Settings are stored permanently, even during power cuts. Clock auto-adjusts for summer/winter time changes. Made by Resideo (Honeywell brand group): Built by the makers of Honeywell Home controls. Installer-trusted and backed by a 3-year warranty. Reliable, affordable, UK-compatible. Also Replaces Honeywell ST7100: Designed to replace the ST7100 timer. However, rewiring is NEEDED in compatible systems.