Boiler room automation Termojet LIGHT (2 circuits + DHW)

Termojet LIGHT is a boiler room controller with two mixing circuits and domestic hot water supply. It simultaneously manages underfloor heating, radiators, and a boiler, automatically adjusting the coolant temperature to match the outdoor weather. A colour touchscreen display, OpenTherm 4.0 communication with the boiler, and expansion via the ONE module or Wi-Fi RS — all in one device.

Technical Specifications

How It Works

The controller receives data from an outdoor temperature sensor and calculates the required coolant temperature for each circuit based on the heating curve. Mixing valves automatically maintain the set values: one circuit for underfloor heating (35–45°C), the other for radiators (50–70°C). The boiler receives its setpoint via the OpenTherm 4.0 bus, enabling burner modulation and reduced gas consumption. The weekly schedule allows different modes to be set for each day and each hour — separately for heating and DHW.

The 2×0–10V outputs are designed for connecting pumps or actuators with variable speed. Room thermostats connected via the RS bus correct the calculated temperature according to the actual indoor temperature. The anti-Legionella disinfection function ensures hygienic safety of the boiler by heating the water to the required temperature according to a set schedule. Return temperature protection guards the boiler against cold return flow.

Application Scenarios

• Gas boiler + underfloor heating and radiators. Two independent circuits with different heating curves — the floor and radiators are controlled separately, gas consumption is minimised.
• Boiler room with a storage tank. Priority DHW heating and automatic anti-Legionella disinfection without manual intervention.
• House with two zones. For example, bedrooms and living room with different heating schedules — each zone gets its own weekly timetable.
• Need a third circuit? Connect Termojet ONE — and LIGHT gains an additional mixing circuit via the RS bus.

Advantages of Termojet LIGHT

• Weather-compensated control — coolant temperature automatically follows the weather; the boiler does not overheat the house in mild conditions.
• OpenTherm 4.0 — two-way digital connection with the boiler for precise power modulation and fuel savings.
• 4.3" colour touchscreen — intuitive navigation without a manual.
• 0–10V outputs for variable-speed pumps — lower noise, lower electricity consumption.
• Scalability: ONE adds a circuit, Wi-Fi RS adds remote control.
• IP30 — suitable for installation in boiler rooms with a normal environment.

Termojet LIGHT and Heat Pump

Weather-compensated control is the key feature for heat pumps. The controller automatically lowers the coolant temperature when outdoor temperatures are above freezing, improving the pump's coefficient of performance (COP). Low-temperature underfloor heating circuits at 35–40°C are the optimal operating mode for most air-to-water heat pumps. Learn more about heat pump integration on the Termojet heat pump website.

Frequently Asked Questions

How many heating circuits does Termojet LIGHT control?
Two mixing circuits (e.g. underfloor heating and radiators) plus a DHW circuit (boiler). A third mixing circuit requires the Termojet ONE module.

What is the difference between LIGHT and PROFI PLUS?
PROFI PLUS controls three mixing circuits instead of two and supports solar collectors with PWM pump control. LIGHT is the optimal choice for a standard boiler room with two zones.