Timeguard 24 Hour/7 Day Compact Electronic Immersion Heater Timeswitch - NTT03. The Timeguard NTT03 Compact Electronic Immersion Timer is a reliable, energy-saving solution for controlling immersion heaters and other electrical appliances with precision. Operating on a 230V AC / 50Hz supply, it allows up to 4 ON and 4 OFF periods per day, giving users the flexibility to schedule heating exactly when needed. Across the week, this adds up to 28 ON and OFF operations, ensuring that energy is never wasted heating water unnecessarily. With its 1-minute switching interval, the NTT03 delivers pinpoint control for maximum efficiency.. A clear Easy View backlit screen displays the current status, complemented by mains and output indicator LEDs for instant feedback. The user-friendly interface includes large push-buttons for quick setup and a self-cancelling override function that lets you temporarily skip to the next programme. For added convenience, the 1- or 2-hour boost mode provides instant extra heating when needed, while automatic summer/winter time changeover ensures the schedule stays accurate year-round.. Compact and durable, the NTT03 can be flush or surface mounted with a minimum back box depth of 32mm, making it suitable for a wide range of installations. Built to Class II double insulation standards, it offers long-term reliability and safe operation in temperatures between 0°C and 40°C. Rated at 16A (3.68kW resistive load), this timer is ideal for immersion heaters, lighting, and other household applications.