In the condensing boiler Radiant R2K 24, the water vapor in the flue gases is condensed to recover latent heat, significantly increasing energy efficiency compared to a standard boiler.

Unlike traditional boilers that dissipate part of the sensible heat to avoid corrosive condensation, condensing boilers exploit this heat for more efficient heating. Opting for a condensing boiler means not only benefiting from modest installation costs but also reducing energy consumption by up to 20%, especially when replacing an older system.

Annual Maintenance and Safety

To ensure that the boiler maintains its safety and efficiency performance, it is essential to subject it to regular maintenance every year. The annual review is vital to ensure the safety and proper ongoing operation of the device.

Annually or at the Start of the Winter Season

  • Regularly check the pressure shown by the pressure gauge.
  • Check the batteries of the room thermostat.
  • Ensure that the heating system's pressure is between 1 and 1.5 bar.
  • Contact qualified personnel for maintenance and cleaning.

Maintaining Heating System Pressure

It's essential to check the heating system's pressure quarterly, ensuring it's between 1bar and 2bar. This check should not be neglected even during the summer months, as the radiator water is used for hot water production. A drop in pressure can interrupt the boiler's operation.

To adjust the pressure, use the filling tap under the appliance. Open it to bring the pressure to 1.5bar, then close it.

Suggested Temperatures

The Radiant R2K 24 boiler can always produce the temperature you want for heating according to your needs. You can adjust the temperatures via the control panel, but we suggest setting the hot water temperature (DHW) to the minimum necessary due to limescale and domestic hot water (DHW) considerations.

Attention to temperature settings:

  • The heating temperature setting refers to the radiator temperature, not the ambient temperature.
  • The domestic hot water temperature setting should be kept as low as possible to avoid calcification inside the secondary heat exchanger.

Instructions for Cleaning Shower Filters and Heads

Follow our detailed instructions to clean the aerator filters and shower heads of your shower. Preventing limescale buildup is essential to avoid issues with filter removal and fluctuations in water temperature. Proper maintenance ensures the longevity and efficiency of the Radiant R2K 24 boiler.

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Boiler Settings for the Holidays

Before going on vacation, it is important to take some measures to ensure the safety of your Radiant R2K 24 boiler. Even the most modern models can have problems if left inactive for an extended period.

Recommended steps:

  • Close the water valve to avoid leaks during your absence.
  • Disconnect the gas supply as an additional safety measure.
  • Turn off the heat generator to conserve energy and improve safety.

When you return, reactivate these settings in reverse order. You may need to reset the heat generator to correct any errors.

These simple steps will ensure a worry-free vacation, knowing that your boiler is safe.

Efficiency in Hot Water Production

The R2K rapid instant boiler is synonymous with efficiency: equipped with a precision flow meter, it detects hot water usage and regulates the temperature to optimal levels, perfect for high-rise buildings. Easily set the desired temperature, and the system will ensure a constant and immediate supply of hot water.

FAST-H2O Function for Comfort

With the FAST-H2O technology, the sanitary water is preheated in the coil, ensuring rapid and continuous supply, eliminating waiting and waste. This innovative feature enhances the user experience, always ensuring the ideal temperature.

  • Instantaneous hot water supply
  • Elimination of waiting and improved comfort
  • Efficiency and waste reduction

To activate the FAST-H2O function, use the and buttons on the control panel.

Intuitive User Interface

The {name} boiler stands out for its simple and intuitive user interface, thanks to the collaboration with NORDGAS. The {manufacturer}'s control panel is designed to be user-friendly, with clear buttons and a display that accurately reports errors, allowing for quick problem diagnosis and resolution.

Simple Error Diagnosis

Common errors such as no flame, thermal fuse interruption, or lack of water in the system are clearly reported on the display. This allows users to quickly identify the issue and take appropriate measures, such as reactivating the system or refilling the system. The boiler is also equipped with safety features like anti-freeze and preheating of sanitary water, ensuring optimal operation in all conditions.

  • Error 01: No flame, which can occur if the gas tap is closed or if the meter has been changed. Press the button. In all other cases, if it does not restart, call a technician.
  • Error 03: Flue side thermal fuse tripped. Press the button. If it does not restart, call a technician.
  • Error 04: No water in the system. Refill the system via the black cylindrical tap under the boiler, keep an eye on the pressure gauge above the display, and close the refill tap when the pressure reaches 1.2 or 1.5 bar. The error resets itself, followed by an approximately 2-minute venting procedure. Please wait.
  • Error 18: Insufficient circulation. This error may be caused by particularly dirty magnetic filters. Check the magnetic filter at the boiler inlet with a technician to restore the circulator flow rate.


These refer not to errors but to functions currently in operation:

  • F08 Anti-freeze function for heating active: If the boiler is external and reaches a very low temperature, this procedure activates to prevent the technical water from freezing. Please wait for the operation to complete.
  • F33 System Venting Cycle: This usually happens during the reset of error E04. Once the {manufacturer} {name} boiler pressure is restored, it performs this function for about 2 minutes. Please wait for the operation to complete.
  • FH Fast H20: The boiler is preparing to preheat the sanitary water. Please wait for the procedure to complete.

Energy Efficiency and Quietness

{manufacturer} has revolutionized energy efficiency with its boiler series, offering exceptional performance in terms of both gas and electricity consumption. These models, besides being extraordinarily quiet (about 55 decibels), boast reduced gas consumption, thanks to their 9 flame modulations and proportional temperature control. Electrical consumption is also minimized, thanks to the modulating WILO circulator and optimized standby consumption.

General Usage Information

To maintain the safety, efficiency, reliability, and performance characteristics that distinguish the device, it is necessary to perform annual maintenance. Annual maintenance is essential for the safety and continuous use of the R2K 24 device.

Warnings for the Use of Electric Energy

For safe use of the boiler, it is important to follow some basic rules:

  • Do not touch the appliance with wet or damp body parts and avoid doing so barefoot.
  • Avoid pulling electrical cords and ensure they are not damaged.
  • Do not expose the appliance to adverse weather conditions such as rain or direct sunlight, unless otherwise indicated.
  • In case of damage to the electric cord, immediately turn off the appliance and contact a qualified technician for replacement.

Additionally, ensure that the boiler is installed, put into operation, and maintained by authorized technicians to guarantee the validity of the warranty and safety in use. Improper use of the appliance and any unauthorized alterations could pose safety risks.

In Case of Gas Odor

  • Do not operate electrical switches, the phone, or any other device that may generate electrical discharges or sparks.
  • Immediately open doors and windows to create an air exchange that can quickly clear the room.
  • Close the gas taps.
  • Request the immediate intervention of professionally qualified personnel.

Guide to Components and Spare Parts

This section is dedicated to providing a complete overview of the various components and spare parts available for the R2K 24 boiler. You will find detailed information on each part, from its main function to advice on when it might need to be replaced.

Temperature Adjustment

On the control panel of the Radiant R2K 24 condensing boiler, you can find all the operational information. You can set the temperatures for heating or hot water by pressing the + and - buttons next to their respective symbols: Faucet and Radiator. After pressing, the boiler displays the set temperature for only a few seconds.

Normally, the boiler shows the flow temperature, to be interpreted as the internal temperature of the boiler. As a result, you will see the temperature rise even in summer when the Radiant R2K 24 boiler produces hot water, while in winter it can be interpreted as the current temperature of the radiators.

Using the + and - buttons at the top for heating and at the bottom for domestic hot water, you can choose the desired temperatures for heating. We suggest:

  • From 25°C to 38°C if you have underfloor heating.
  • From 55°C to 65°C if you have radiators made of aluminum or steel.
  • From 45°C to 60°C if you have cast iron radiators.

For domestic hot water, you can choose the temperature using the + and - buttons at the bottom. We suggest a temperature between 38 and 45°C.

The general advice for the temperature of domestic hot water is to keep it as low as possible, especially if your water supply provides very hard water (over 30°F).

Energy Efficiency of the {manufacturer} Heat Exchanger

The patented heat exchanger from {manufacturer} represents a qualitative leap in energy efficiency. Its concentric coil, managing both sanitary water and heating, lowers the exchanger temperature for better condensation. This not only improves thermal efficiency but also reduces lime scale formation, a significant benefit in areas with hard water like Modena.

The {manufacturer} R2K 24 boiler also includes an innovative system that induces vibrations in the piping to further reduce lime scale deposits, a step forward towards long-term sustainability.

Boiler Circulator Radiant R2K 24

Energy Saving with the Modulating Pump for Boilers

The introduction of variable speed modulating pumps in modern boilers is a revolution in terms of energy saving and cost reduction. These pumps, regulated by an advanced electronic system through a second connector, are capable of varying their speed from 0 to 100% according to the real needs, maximizing the efficiency of the system. Their use, mandatory in new boilers, demonstrates a commitment to solutions that combine excellent performance with care for the environment and household economy.

3/8 Automatic Plastic Air Purger for Radiant R2K 24 boiler

Automatic Plastic Air Purger

The plastic automatic air purger, used as an insert in the purging housing in the pump manifold, is a key component in the Radiant R2K 24 boiler. This small element plays a vital role in ensuring the efficiency of the heating system by eliminating air from the system.

Made of durable plastic, this air purger is designed to easily fit into the dedicated housing in the pump manifold. Its use is particularly recommended to prevent air accumulation in the boiler's hydraulic circuitry, especially in systems with a lot of aluminum where this problem is more frequent after periods of inactivity (summer).

Regularly checking and replacing the air purger and the system pressure is essential for maintaining uninterrupted operation at the start of the heating season. Its functionality is crucial for the proper operation of the entire domestic heating system.

3/8 Automatic Air Purger for Radiant R2K 24 boiler

3/8 Automatic Air Purger

The 3/8 automatic air purger is a fundamental component in the Radiant R2K 24 boiler to ensure the elimination of air in the heating system. This small but essential device plays a critical role in maintaining the efficiency of the heating system.

Despite its low cost, this component is vital to ensure that there is no trapped air in the radiator system, especially for aluminum ones, where the presence of air can be a frequent problem, particularly after long periods of inactivity like during the summer.

Checking the functionality and replacing the air purger is always advised to prevent circulation problems at the beginning of the heating season. Its efficiency is crucial for the proper operation of the entire domestic heating system.

Safety Systems according to the ErP Directive

The construction and installation of boilers in Europe are strictly regulated by a series of European standards, aimed at ensuring safety, energy efficiency, and reduction of environmental impact.

One of the main reference regulations is the ErP (Energy-related Products) Directive, which imposes stringent requirements in terms of energy efficiency and emissions for all energy-related products, including boilers. This directive is accompanied by specific UNI EN standards for each type of boiler, detailing the technical and safety standards to be respected.

The R2K 24 boiler therefore includes:

The Safety Thermostat, located on the heating supply, intervenes by blocking the gas flow to the burner in case of overheating of the water in the primary circuit. It is essential to never deactivate this safety device.

The Flame Ionization Detector ensures safety by shutting down the boiler in case of gas absence or incomplete ignition of the main burner.

The Antifreeze Device activates the burner to maintain the water temperature above 5 °C, preventing freezing of the system.

The Hydraulic Safety Valve, set at 3 bar, protects the heating circuit. It is advisable to connect it to a siphoned drain and not use it to empty the circuit.

Possible Improvement Works

The condensing boiler Radiant R2K 24 requires special attention to the correct installation of the flue pipe. Especially in horizontal sections, condensation can form, compromising the functionality of the fan. It is not uncommon to see installations where the flue pipe (especially if corrugated) forms a siphon, causing the boiler to produce very loud noises. It is essential to have a qualified technician ensure that the pipes are in optimal condition.

Integrating a Gas Tap with a Test Well

Not always does the meter provide a connection for instrumental tightness testing. A useful tip is to replace the gas tap under the boiler with a valve with a well equipped with an instrumental take-off, essential for the tightness test of the system. This element can be crucial in case of inspections and safety checks and certainly facilitates the maintenance of the R2K 24 boiler.

In fact, during the maintenance of the appliance, it is mandatory to perform a suitable test like UNI 11137:2019 that verifies the correct tightness of the gas system.

Flushing the Heating System

Flushing the heating system is crucial to prevent clogging of the primary exchanger of the Radiant R2K 24 boiler. Over time, especially in cast iron or aluminum systems, a metallic sludge can form that can clog the narrow passages of the exchanger.

After flushing the system, it is highly recommended to install a magnetic sludge filter on the Radiant R2K 24 boiler. This filter plays an essential role in protecting the exchanger from the buildup of dirt and debris, ensuring greater efficiency and longevity of the heating system.

Additional improvements can include the installation of an advanced thermostat with relay function. This device allows for more effective management of heating hours, helping to optimize energy consumption.

Accessory Guide

Elevate the performance of your R2K 24 boiler with our selection of essential accessories, we recommend:

  • New Generation Programmable Thermostat: Manage ambient temperature with precision and ease, thanks to intelligent programming and remote control.
  • Magnetic Filter Dirt Separator: Protects your heating system from harmful residues, ensuring greater longevity and efficiency.

Magnetic Filter for Heating

Considered the best accessory to block the entry of dust and debris from the heating system into the device.

Installing the magnetic filter on the heating return line is a crucial step in ensuring the longevity of the boiler. This device effectively separates and retains any particles that could cause damage or inefficiencies in the device, including preventing blockage of the primary exchanger. Its presence also ensures less stress on the diverter valve, increasing its reliability and reducing the risk of malfunctions.

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Polyphosphate Dosing Pump

If the hardness of the tap water exceeds 20 French degrees, we suggest equipping the Radiant R2K 24 boiler with a polyphosphate doser.

Polyphosphates, available in powder or liquid form, are mixed with the cold water entering the Radiant R2K 24 boiler, significantly reducing limescale formation. These additives are essential for maintaining efficiency and extending the lifespan of the device and must be regularly replenished.

There are several models of polyphosphate dosers, the most common ones are:

  • Powder Polyphosphates
  • Liquid Polyphosphates

Each type of polyphosphate requires a specific system for mixing.

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Room Thermostat and Programmable Thermostat

For optimal temperature control in your home, consider installing a thermostat or programmable thermostat for your boiler.

These devices allow you to regulate and program the temperature precisely, adjusting it to your daily needs. A programmable thermostat, in particular, offers the possibility to set different programs for specific days and times, optimizing comfort and reducing energy costs.

There are various models available, including:

  • Daily Programmable Thermostats
  • Weekly Programmable Thermostats
  • New Generation Thermostats with Remote Control

The choice of model depends on your specific needs and the configuration of your heating system.

Daily Programmable Thermostat

The daily programmable thermostat is an effective solution for daily temperature control in your home.

This device allows you to set the desired temperature for each individual day, enabling flexible management adaptable to your daily routines. It is ideal for those seeking simple yet precise control of home heating, with the ability to adjust settings according to variations in their daily schedule.

Typical features of a daily programmable thermostat include:

  • Easy and intuitive programming
  • Precise temperature adjustment
  • Energy-saving functions

This type of thermostat is an optimal choice for those who want to combine comfort and energy efficiency without the need for complex weekly programming.

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Weekly Programmable Thermostat

For advanced and personalized home temperature management, the weekly programmable thermostat is an excellent choice.

This device allows for setting different temperatures for various days of the week, perfectly adapting to different weekly routines. It is ideal for those who need detailed heating control, with the ability to set lower temperatures on days when the home is empty and higher when it is occupied.

Key features of the weekly programmable thermostat include:

  • Flexible programming for each day of the week
  • Advanced energy-saving functions
  • Intuitive user interface for easy programming

A weekly programmable thermostat is perfect for those seeking a balance between comfort, convenience, and energy efficiency, providing precise control of the home climate.

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Advanced New Generation Thermostats

New generation advanced thermostats offer cutting-edge technologies for optimal home climate control.

These devices stand out for their learning capability and adaptation to user habits, automatically adjusting the temperature based on daily and seasonal patterns. With features like remote control via smartphone and integration with home automation systems, they offer an unprecedented level of convenience and energy efficiency.

Salient features of these thermostats include:

  • Wi-Fi connectivity and remote control
  • Integration with voice assistants and smart home systems
  • Learning algorithms for automatic temperature optimization

For those seeking the utmost efficiency, convenience, and personalization in home temperature control, an advanced new generation thermostat is the ideal choice.

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To view the boiler data from info menu you just have to press the INFO key. The info code will be displayed on the left side of the screen and its relative value will be displayed on the centre of the screen.
Use keys ‘ + ’ and ‘ - ’ of the heating circuit to scroll through the list of displayed data. To exit display mode press the INFO ‘ i ’ key.

Info Code Description
D0 domestic Circuit Probe Temperature
D1 external Probe Temperature
D2 fan Speed
D3 bottom Area Probe Temperature [if Area Board Installed]
D4 return Probe Temperature
D5 solar Collector Temperature [if Solar Board Installed] (Scs)
D6 solar Boiler Temperature (Bottom) [if Solar Board Installed] (Sbsi)
D7 solar Boiler Temperature (Top) [if Solar Board Installed] (Sbss)
D8 solar Collector Probe Temperature 2 [if Solar Board Installed] (Scs2)
D9 extra Solar Boiler Temperature [if Solar Board Installed] (Sbs3)

Anomaly Reporting Codes R2K 24

To display the last 5 anomaly reporting codes, from the most recent in chronological order, activate OFF mode using the central button and hold down the INFO button for 5 seconds. To scroll through the list of stored anomalies, use the PLUS and MINUS buttons of the heating system. To reset the anomaly history, press the RESET button. To exit the display environment, press the INFO button.

Anomaly Code Possible Cause Remedy Reset
E01 Flame lock without flame ignition
  • No gas; Check the supply network
  • Broken or grounded ignition electrode; Replace it
  • Broken gas valve; Replace it
  • Slow ignition set too low; Adjust the minimum or slow ignition
  • Inlet pressure too high (only for LPG boilers); Check the maximum regulation pressure
Manual reset (Press the reset button)
E02 Safety thermostat (95°C)
  • Broken or disconnected thermostat cable; Check the electrical connection
  • Broken thermostat; Replace it
Manual reset (Press the reset button)
E03 Safety thermal fuse for fumes (102°C)
  • Broken thermal fuse; Replace it
  • Disconnected thermal fuse cable; Check the electrical connection
Manual reset (Press the reset button)
E04 Water shortage in the system
  • Insufficient water pressure in the system (below 0.3 bar); Fill the system
  • Disconnected water pressure switch cable; Check the electrical connection
  • Broken water pressure switch; Replace it
E05 Heating sensor
  • Broken or uncalibrated sensor (Resistance value 10 kOhm at 25 °C NTC); Replace it
  • Wet or disconnected sensor connector; Check the electrical connection
E06 Sanitary sensor
  • Broken or uncalibrated sensor (Resistance value 10 kOhm at 25 °C NTC); Replace it
  • Wet or disconnected sensor connector; Check the electrical connection
E15 Return sensor
  • Broken or uncalibrated sensor (Resistance value 10 kOhm at 25 °C NTC); Replace it
  • Wet or disconnected sensor connector; Check the electrical connection
E16 Fan
  • Broken fan board; Replace it
  • Broken fan; Replace it
  • Malfunctioning electrical supply cable; Replace it
E18 Insufficient circulation
  • Clogged heat exchanger; Clean the heat exchanger or replace it
  • Broken circulator or dirty impeller; Clean the impeller or replace the circulator
E21 Generic internal board error Incorrect signal recognition by the microprocessor of the modulation board; If the modulation board does not reset the error automatically, replace it Automatic
E22 Parameter programming request Memory loss of the microprocessor; Reprogram parameters Manual reset (Remove power)
E35 Parasitic flame
  • Malfunctioning detection electrode; Clean or replace it
  • Malfunctioning detection electrode cable; Replace it
  • Malfunctioning modulation board; Replace it
Manual reset (Press the reset button)
E40 Power supply voltage Power supply voltage out of operating range (below 160 volts); Check the electrical supply network (The error deactivates automatically as soon as the power supply voltage returns within the required limits) Automatic


Discover the answers to the most frequent questions about the Radiant R2K 24 boiler model. This quick guide has been compiled to provide clear and direct information based on the common questions from our users.

Hot Water takes forever to reach the shower/bathroom !!

The delay in hot water reaching the bathroom is often caused by a buildup of dirt in the aerator or showerhead holes. This buildup can reduce water flow, consequently slowing down the flow of hot water in the pipes. Cleaning these accessories from limescale can usually restore the speed of the hot water arrival.

Additionally, if the pipes connecting the bathroom to the boiler are made of iron, they might absorb some of the water's heat, lengthening the time for hot water to arrive. The presence of iron pipes can thus affect the timing of hot water delivery to the bathroom.

Loud Noises During Operation

If your Radiant R2K 24 boiler makes loud noises during operation, first check the system pressure. Too low a pressure can be the cause. Otherwise, in this condensing boiler, it could occur due to lack of maintenance.

Indeed, the heat exchanger tends to slightly oxidize during operation and over time a large amount of dirt can accumulate in the condensate siphon. Regular maintenance is essential to reduce the risk of noises or machine shutdowns.

Opentherm Protocol Support by the Boiler

YES: The boiler is equipped with non-powered thermostatic connections, compatible with Smart Thermostats or Remote Controls. This allows the use of advanced functions such as:

  • Adjusting the domestic hot water temperature: Ideal for R2K 24 boilers installed in hard-to-reach areas.
  • Adjusting the radiator temperature: With the Opentherm chronothermostat, it is possible to adjust the radiator temperatures directly from the boiler.
  • Setting operating times for domestic hot water: A feature that helps to reduce the maintenance costs of the boiler for models with storage tanks.
  • Fault Management: Using the Opentherm 2 protocol or a specific remote control from Radiant.
  • etc...

Pressing the buttons to adjust the heating, the temperature does not change.

The button panel is sensitive to repeated presses after years of operation. Often, the malfunction of the adjustment buttons is due to the absence of a thermostat, which has led to the exclusive use of the boiler's buttons.

In light of this, it is suggested to install a new control board to restore the correct functioning of the button panel, but also to integrate a thermostat to continue adjusting the heating from another, more reliable, and less expensive device.

Downloadable Manuals