The Honeywell ST9100S is a single-channel, 1-day timer designed for controlling a single heating zone or combi boiler applications. It features a built-in Service Interval reminder that can be adjusted to display a message or restrict action when an annual system service is due. The timer utilizes a Line of Text (LoT™) display, providing clear, plain English instructions with button or slider use. It offers up to 3 events per day and automatically adjusts for summer and winter time changes. The unit has a Single Pole, Double Throw (SPDT) relay and operates on a 230V AC, 50Hz power supply with a 10W power consumption. The operating temperature range is 0 to 40°C, and it conforms to EN60730-2-7. Additional features include temporary or permanent override facilities and a large backlit display. It is suitable for single switch boxes and provides options for surface wiring.