Description
The OP-IHTDIGI is a compact digital timeswitch intended for controlling immersion heaters and other general-purpose loads in domestic and light-commercial settings. It offers both 24-hour and seven‑day programming, up to 24 independent ON/OFF events and a minimum switching resolution of one minute, so you can build fairly detailed heating schedules or set short-duration events such as boost periods.
Functionally this is a surface‑mount, hardwired controller with volt‑free SPDT switching contacts (a brass link is fitted for direct immersion control and can be removed to make the contact volt‑free). It runs from the normal UK mains range (220–240V AC) and is intended where a reliable, low‑cost time control is required rather than an advanced smart thermostat or app‑based product.
Key specifications
- Product model: OP-IHTDIGI (Optimum / TFC Group)
- Supply: 220–240V AC, 50Hz
- Load rating: 16A resistive, 4A inductive (SPDT contacts)
- Programming: 24‑hour and 7‑day modes, up to 24 ON/OFF programmes, 1‑minute resolution
- Special modes: Fixed ON, Timed, Fixed OFF, Random and Countdown
- Random function: varies switching times by ±28 minutes around a programme
- Running reserve: approx. 2 months at 20°C (retains programmes during power loss)
- Mounting: surface mount backplate; earth park terminal and cable clamps provided
- Dimensions & weight: 50 × 72 × 122 mm; ~0.220 kg
Practical operation
The timer is aimed at anyone who wants predictable, repeatable control of a heater or other resistive load without relying on central heating timers or internet services. In day‑to‑day use you set the clock then enter timed programmes in either a simple 24‑hour cycle or a full week‑by‑week schedule. The minimum 1‑minute step makes it possible to run short boost periods (for example a 10‑ or 15‑minute top‑up) and the manual override options let you put the output into fixed on, fixed off, countdown or temporary timed modes without reprogramming the stored schedule.
The Random mode is handy where you want to give the appearance of occupancy by varying the on/off times within a defined window; the unit alters programmed times by up to 28 minutes either side of the set point. Because the control is local and mechanical/electrical rather than cloud‑connected, it’s simple and predictable — ideal for landlords, self‑builders and tradespeople fitting economical controls to hot‑water circuits.
Installation and wiring notes
The OP‑IHTDIGI is designed for surface mounting onto a backplate and should be installed in accordance with the current wiring regulations. It includes a removable brass link so it can be wired as a mains switching device (immersion heater direct control) or converted to a volt‑free contact arrangement for control of an external contactor. The unit provides an earth park terminal and cable clamps for a tidy, secure installation.
Typical terminal layout used on the product places supply live on terminal 3 and neutral on terminal 1, with the switched live (load) on terminal 4; a pre‑fitted link bridges terminals 2 and 3 for direct immersion installations. Because of the modest inductive rating (4A), any motor or inductive load larger than that — or installation controlling a relay/contactor — should be wired so the timer switches the contactor coil rather than the load directly. The manufacturer’s installation sheet contains the exact wiring diagrams and safety instructions and a qualified electrician should be used where required.
Suitability and limitations
This is a functional, no‑frills programmable timer rather than a smart or adaptive controller. It suits: immersion heater circuits, simple off‑peak switching, and any resistive load within the stated 16A limit. It is not recommended for driving discharge or LED lighting directly without a contactor, and its 4A inductive rating means high inductive loads need a contactor. Because it is a surface‑mounted module with exposed terminals under the cover, the usual precautions apply — do not mount it on flammable surfaces, allow an adequate 300 mm air space, and comply with earthing and isolation rules.
For buyers who want a straightforward, programmable hardware timer with a useful set of manual modes and the added option of the Random function, the OP‑IHTDIGI is a practical choice. If you require app control, remote scheduling or integration with a home automation system, this model does not offer those features and you should consider a Wi‑Fi or smart relay alternative.
