ISE 3-0004-007 KNX RF Radiator Thermostat | Multi

A radiator thermostat is truly smart when it can be retrofitted in existing installations and still functions like a normal thermostat in everyday use. This KNX RF thermostat of the “Multi” variant controls directly at the valve, communicates via the KNX RF Multi standard, and offers features that noticeably improve comfort and operational reliability during winter.

• KNX RF Multi Radio: It communicates as an RF1.M (Multi) device in the KNX RF Multi standard over 868.3 MHz, 868.950 MHz, 869.525 MHz, and 869.850 MHz with up to 25 mW transmission power and typically achieves a 100 m transmission range in free field.
• KNX Secure and Long Frames: It fully supports KNX Secure, processes Long Frames, and can be updated via firmware over KNX RF, ensuring security and functionality are maintained even with later project changes.
• Battery operation for retrofitting: Powered by 2 x AA batteries, the battery life typically lasts for 2 heating periods or up to two years, eliminating the need for a separate power supply at the radiator.
• Control range at the radiator: The adjustable control temperature ranges from 5 °C to 30 °C, and the setpoint is readable on the device, covering typical comfort, night, and frost protection requirements directly.
• Valve actuator with high actuating force: Connection is via M30 x 1.5 thread, and the actuating force is up to 120 N, enabling robust operation for many common radiator valves.
• Diagnostics and valve protection: It issues fault messages such as detecting a stuck valve, sends an “in operation” heartbeat, and performs automatic valve flushing to prevent limescale build-up and malfunctions.

KNX RF Multi and System Requirements

The thermostat controls radiator valves via KNX and transmits its telegrams over the KNX RF Multi radio standard, which is especially interesting for retrofitting when no bus cable is present at the radiator or cable routes should be avoided. For integration into a KNX installation, a KNX RF Multi/TP media coupler is required, which converts the radio telegrams into the TP line or the KNX topology. This system component is as important for project planning as the thermostat itself. The device operates on several frequencies in the 868 MHz range with a maximum transmission power of 25 mW, while the typical free field range is 100 m, which can vary significantly indoors depending on construction, reinforced concrete, shafts, and radiator recesses, and should therefore be considered when positioning the media coupler and segmenting radio areas. For security-conscious installations, full support of KNX Secure is relevant because it allows secure transmission of telegrams, and support for Long Frames helps when modern device profiles or larger user data are used over the radio link. Practical for the lifecycle is also that updates are possible via KNX RF, allowing functionality and security levels to be maintained in the field without removal.

Control and Operating Modes

In operation, the thermostat can be operated directly on the device or via KNX in S-Mode, allowing local interventions at the radiator even if the room logic is centrally controlled via push-buttons, visualisation, or automation rules. Two options are available for the actual temperature: an internal temperature sensor or the use of a measured value via a communication object, which is important for selecting the control strategy because the temperature at the radiator is often higher than the room air and external sensors at a better measuring point can provide more accurate room values. The control temperature from 5 °C to 30 °C covers typical heating profiles, and four operating modes support clear logic in everyday use: comfort, standby, night mode, and frost protection. Additionally, summer and winter operation are provided, which is relevant for systems with seasonal switching or operating states outside the heating period, as unnecessary actuator movements can be reduced. A boost function enables short-term, rapid heating when, for example, more heat is needed briefly after airing or spontaneous room use, without having to permanently set a higher setpoint. For integration with KNX scenes, scenes can be individually configured, and for rooms with multiple radiators, grouping via main/sub device dependencies is planned so that several thermostats respond jointly to the same setpoint, mode, or schedule, preventing unstable control caused by different radiator settings. Forced positions are adjustable, which is relevant in practice for service, maintenance, or overarching safety and energy-saving strategies, for example when a central logic should enforce a defined valve position.

Planning for Operational Reliability

For battery-powered actuators, diagnostics and protection functions are decisive for purchase, as heating operation in winter must not depend on undetected faults. The device detects battery status, enabling timely maintenance, and issues fault messages, for example if a valve is stuck, allowing service cases to be reliably detected in KNX monitoring or visualisation. An “in operation” heartbeat communication object additionally supports monitoring because not only errors but also failures or radio problems can be identified as a missing signal. The automatic valve flushing serves to prevent limescale build-up, which is especially important during longer idle periods or transitional times, as valves are more prone to sticking then. For projects requiring differentiated temperature control, setpoints for each mode and heating programme can be configured, allowing, for example, night setback, standby during absence, and frost protection to be clearly separated without constantly adjusting the setpoint manually.

Mechanics and Valve Compatibility

Mechanically, the thermostat sits directly on the radiator valve and uses an M30 x 1.5 threaded connection, which is very common in the European radiator market and thus increases the chance of compatibility, although differing valve standards in existing systems should still be checked during planning. The maximum actuating force of 120 N is a relevant value because it determines how reliably the device can close and open even with stiff valves or higher differential pressures. The operating temperature range of 0 °C to +50 °C covers typical radiator environments, and the IP20 protection rating makes clear that the device is intended for dry indoor rooms. With tight niches or coverings, the dimensions are important, specified as 53 x 85 x 70 mm (W x L x H), so that installation can be realistically assessed even for radiators near windows or behind cladding.

Planning in ETS

Commissioning requires ETS 6.2 or higher, which should be considered in the project environment and team workflow, especially if several trades or service providers work with different ETS versions. During the selection phase, it makes sense to structure project requirements along three questions: How is the actual temperature recorded, how are multiple radiators per room grouped, and how should monitoring for radio and battery issues be handled? If external room temperature sensors are used, the thermostat can be supplied with a room value via communication objects, while the control variable still acts directly at the radiator, increasing comfort and reducing typical measurement errors at the valve location. For grouping multiple thermostats, main and sub devices are logical because this allows a room to be mapped as one control zone without each radiator needing to be operated separately, and scenes help integrate setpoints and modes into a general building logic, for example for absence or night operation. KNX Secure is especially a decision criterion when radio telegrams are transmitted in multi-occupancy buildings or sensitive environments, and the ability to update via KNX RF supports a sustainable operating concept because adjustments and bug fixes can also be implemented in existing installations.

Manufacturer

ISE develops KNX components with a strong focus on practical retrofitting and clean integration into ETS projects. The brand is particularly present in the KNX RF environment and focuses on features that facilitate maintenance and diagnostics during operation. A key focus is on secure communication mechanisms such as KNX Secure and on long-term operable devices that remain updateable in the field. This makes the portfolio well suited for installations that should be expanded without additional cabling while maintaining a typical KNX project structure.