ATTACK Condensing KT 48 - wall-mounted gas condensing boiler with instantaneous DHW heating

Product detailed description

ATTACK Condensing KT 48 is the flagship of the wall-mounted condensing KT range and its most powerful member. While the smaller KT 20 and KT 28 models cover the needs of a typical family home, the KT 48 is intended for situations with greater heat demand – larger households with higher heat loss, family houses with a swimming pool or large-area underfloor heating, as well as smaller businesses, office spaces, shops or service premises that require a stable yet economical source of heat and hot water.

The boiler works with instantaneous DHW heating – it heats hot water immediately on demand, without the need for a storage tank, with a high comfort flow rate thanks to its generous 48 kW output. This means practically unlimited hot water comfort even with simultaneous draw-off from multiple outlets (bathroom, kitchen), which is often a limiting factor with smaller condensing boilers.

Key features

• High modulated output of 9.5 – 48 kW – the boiler smoothly adapts to the current heat demand.
• Condensing technology with high seasonal efficiency (class A according to ErP) – it also utilises heat from the flue gases that would otherwise escape through the chimney in a conventional (atmospheric) boiler.
• Instantaneous DHW heating with high comfort flow rate, also suitable for households with multiple bathrooms.
• Ready for cascade connection – multiple KT 48 boilers can be linked into a single system for an output exceeding the capabilities of a single boiler.
• Communication via the OpenTherm protocol – supports OT36A / OT36B / OT80 room thermostats and the OT81 wifi modem for control via a mobile app.
• Option to connect an outdoor temperature sensor (401060001) for weather-compensated control.
• Compact wall-mounted design despite the high output.
• Quiet operation thanks to the modulated flue gas fan.

Technical parameters

Who is the KT 48 suitable for

With an output of 48 kW, this boiler ranks among the most powerful wall-mounted condensing units on the market. In practice it is suitable for: larger new-build houses with higher heat loss, older family houses with poorer insulation, houses with a swimming pool (pool water heating via a heat exchanger), buildings with higher simultaneous DHW consumption (multiple bathrooms), and smaller commercial premises (shops, offices, service businesses). If a single 48 kW boiler is still not enough, or if redundancy is desirable for operational reasons (backup in case of failure), two or more KT 48 boilers can be connected in a cascade.

Cascade connection

For premises with higher heat demand, or where a backup is desirable, we offer a complete set of accessories for the KT 48 boiler for cascade connection of multiple units into a single heating system:

• 401150013 – mounting frame for a single KT 48 boiler (standalone installation or the first boiler of a future cascade),
• 401150014 – mounting frame for two KT 48 boilers side by side,
• 401150056 – cascade interface, required for every additional boiler in the cascade except the first,
• 401150061 – 0-10V interface for boilers controlled by an analogue signal instead of OpenTherm (e.g. when connecting to a higher-level building management system),
• 401150096 – cascade controller, which controls the operation of the whole cascade as a single unit.

Thanks to the cascade, a combined output several times higher than that of a single boiler can be achieved, while the system distributes the load among the individual boilers and, in the event of a failure of one boiler, the others can continue to supply heat – which is not possible with a single large boiler.

Installation and connection

Installation, connection to the gas supply, electrical network, flue gas exhaust and initial commissioning must only be carried out by a professionally qualified person (authorised gas fitter / ATTACK service technician). The boiler requires connection to: a natural gas supply with appropriate pressure, a heating circuit (flow/return), a cold and hot water supply for instantaneous heating, a 230 V electrical network, and condensate drainage (if required, with a neutralisation device in accordance with local wastewater regulations). Flue gas exhaust can be solved concentrically (60/100 mm) or with a twin-pipe system (80/80 mm) depending on the layout of the building.

Before initial start-up, an inspection of the gas installation and the point of consumption is required in accordance with applicable legislation. Initial commissioning by an authorised technician is also a condition for the full 24-month warranty to be recognised.

Compatibility and related products

For the KT 48 boiler we recommend the following accessories, which are part of this delivery of goods: outdoor temperature sensor 401060001 (weather-compensated control), room thermostats OT36A (wireless) or OT36B (wired, 2-wire connection), OT80 (room thermostat for the wifi modem) together with OT81 (wifi modem for the mobile app), and the complete set of cascade accessories 401150013 / 401150014 / 401150056 / 401150061 / 401150096. The same accessories (except for the cascade frames and interface, which are specific to the KT 48) are also compatible with the KT 20, KT 28, KST 24 and KZT 25 models.

Maintenance and service

We recommend having a regular annual service inspection carried out by an authorised service, which includes checking the burner, heat exchanger, joint tightness, expansion vessel function, cleanliness of the condensate drain siphon, and inspection of the flue path. Regular servicing extends the boiler's service life and is also a condition for maintaining the warranty.

Frequently asked questions

What is the difference between the KT 48 and the smaller KT 20 / KT 28 models?

The main difference is output – the KT 48 offers significantly higher heating and instantaneous DHW heating output, which makes it suitable for larger buildings or premises with higher heat and hot water demand. The other principles (condensing technology, OpenTherm control) are the same.

What exactly does "instantaneous DHW heating" mean?

The boiler has no built-in hot water tank – it heats water immediately at the moment of draw-off, by flow through a secondary heat exchanger. The advantage is an unlimited amount of hot water (limited only by the boiler's output), the disadvantage is somewhat lower comfort at very high simultaneous draw-off compared to a large storage tank.

How does cascade connection of multiple KT 48 boilers work?

Several boilers are hydraulically connected to a common manifold and controlled by a single cascade controller (401150096), which switches on the required number of boilers according to current demand. Each additional boiler in the cascade (except the first) requires the 401150056 interface. The result is a system with a combined output of several boilers and backup in the event of a fault in one unit.

What type of flue gas exhaust does the boiler require?

The boiler operates with forced draught (turbo) and can be connected either to a concentric flue 60/100 mm, or to a twin-pipe intake and exhaust system 80/80 mm, depending on the specific layout of the building.

Is condensate neutralisation required?

At higher outputs and with a larger amount of condensate produced, local wastewater discharge regulations may require a neutralisation device before the condensate is discharged into the sewer – we recommend verifying this with the installation company according to the installation location.

Can the boiler be controlled via a mobile app?

Yes, after adding the OT81 wifi modem (in combination with the OT80 room thermostat), the boiler can be monitored and controlled remotely from a mobile app – temperature setting, heating programmes, notifications about operating states.

How often does the boiler need servicing?

The recommended interval is one service inspection per year, carried out by an authorised service technician. Regular servicing is also a condition for maintaining the warranty.

Can the boiler be connected to a higher-level building management system (BMS) without OpenTherm?

Yes, the 401150061 accessory – a 0-10V interface – serves this purpose, allowing the boiler to be controlled by a standard 0-10V analogue signal instead of digital OpenTherm communication.

Typical application scenarios

Larger family house with higher heat loss: An older, non-insulated building or a house with large glazed areas may have a heat loss that the smaller KT 20 or KT 28 models cannot cover. In such a case, the KT 48 provides sufficient output reserve even on freezing days, without the need for supplementary heating from another source.

House with a swimming pool: In addition to heating and DHW preparation, the boiler's output can also be used to heat pool water via a separate plate heat exchanger (according to the heating system design) – the high output of the KT 48 shortens the time needed to heat the pool water to the required temperature.

Smaller business or service premises: Shops, office spaces, smaller accommodation facilities or premises with higher and uneven hot water consumption (multiple bathrooms) benefit from the high comfort DHW flow rate and modulated output, which adapts to the current operational load.

Cascade boiler room for an apartment building or larger building: Where even a single 48 kW boiler is not enough, two or more KT 48 boilers can be connected in a cascade with a total output ranging from several tens up to over a hundred kW, with the advantage of redundancy in the event of a failure of one unit.

Operating costs and return on condensing technology

A condensing boiler also utilises the heat contained in the flue gases (the condensation heat of water vapour), which would otherwise escape unused through the chimney in a conventional atmospheric boiler. As a result, the KT 48 achieves a seasonal efficiency of around 93%, which, compared to older or atmospheric boilers, results in lower natural gas consumption for the same heat demand. The actual savings depend on the specific building, the heating curve settings and the type of heating system (the highest condensing efficiency is achieved with low-temperature systems, e.g. underfloor heating, where the return temperature is low).

More frequently asked questions

Can the KT 48 be used without the cascade accessories, just as a standalone boiler?

Yes, the KT 48 works fully as a standalone boiler without any cascade accessories – cascade expansion is an optional feature for cases of higher output demand or redundancy.

What is the minimum output the boiler can modulate down to?

The boiler modulates its output within a range of approximately 9.5 – 48 kW, which allows it to work efficiently even at low current heat demand (e.g. outside the heating season, when only preparing DHW) without unnecessary cycling.

Do I need an additional expansion vessel with the KT 48 boiler?

The boiler has a built-in expansion vessel; for larger heating system volumes (large houses, multiple circuits), a heating designer may recommend an additional external expansion vessel – leave this assessment to a designer or installation company.

Is the boiler suitable for underfloor heating?

Yes, condensing boilers achieve the highest efficiency precisely with low-temperature systems such as underfloor heating, where the temperature of the heating water and return is low, which maximises the utilisation of condensation heat.

How long does the installation of the KT 48 boiler take?

The exact time depends on the scope of work (new installation vs. replacement of an old boiler, length of piping runs, flue gas exhaust solution); a typical replacement of an existing boiler usually takes one working day, while a cascade setup or a completely new installation takes longer.

What is the maximum number of boilers that can be connected in a cascade?

The specific maximum number of boilers in a cascade depends on the chosen cascade controller and the heating system design. When designing a larger cascade (more than two boilers), we recommend consulting a heating designer and the ATTACK installation company.

Does the boiler require regular checking of system pressure?

Yes, as with any closed heating system, it is advisable to regularly check the water pressure in the system (shown on the boiler's display or pressure gauge) and top up the system according to the instructions in the operating manual if it drops.

Can the boiler be operated on LPG (propane-butane)?

Conversion to LPG instead of natural gas G20 is available on request – such conversion is carried out exclusively by an authorised service technician with the relevant qualification, usually before initial commissioning.

Warranty

For the ATTACK wall-mounted gas boiler we provide a warranty period of 24 months from commissioning by an authorised service technician, but no more than 30 months from the date of shipment from the manufacturer's warehouse (whichever period expires first). The validity of the warranty is conditional on professional installation, initial commissioning by an authorised ATTACK service, and compliance with regular annual service inspections according to the operating manual. Without confirmed commissioning, the warranty period is counted from the date the boiler is shipped from the factory, but not exceeding the stated 30 months.

The ATTACK Condensing KT 48 is a choice for more demanding installations – high output, hot water comfort and the possibility of cascade expansion make it a practical solution where a standard family condensing boiler is no longer sufficient.

Summary

We classify the KT 48 among condensing boilers for more demanding premises – where high output, great hot water comfort or the possibility of future expansion in the form of a cascade are required. Thanks to the complete range of accompanying accessories (room thermostats, wifi modem, outdoor sensor, cascade frames and controller), the installation can be tailored precisely, from a simple standalone boiler to a full multi-boiler cascade boiler room. We will be happy to advise you when designing a specific setup for your building.