ATTACK 25 EKO COMBI - stationary gas cast iron boiler 25 kW

Product detailed description

ATTACK COMBI - stationary cast iron gas boiler

Stationary gas boilers with a cast iron heat exchanger are among the most durable and time-tested heating solutions on the market. Cast iron as an exchanger material is highly resistant to corrosion and thermal shock, and tolerates less gentle operation (frequent switching, fluctuating return water temperature) better than thin-walled steel or aluminium exchangers. Thanks to this, cast iron boilers have long enjoyed a reputation as robust and reliable appliances suitable not only for ordinary family houses but also for larger buildings, facilities, workshops, small businesses or multi-generational houses with higher heat consumption.

Another advantage of the cast iron body is easy maintenance and serviceability - a cast iron exchanger usually consists of individual sections (segments), which means that if one of them is damaged, only the affected section can be replaced instead of the whole exchanger. In the long term this can mean lower servicing costs compared to one-piece exchangers. The stationary design (a boiler standing on the floor, not wall-mounted) also simplifies installation at higher outputs and makes it easier to connect to a naturally draught chimney, commonly used in both older and newer boiler rooms.

The model you are currently viewing belongs to the ATTACK EKO COMBI range and is rated for a nominal heat output of 25 kW. It is a stationary gas boiler in COMBI design - in the context of this ATTACK cast iron range this means that the boiler itself does not have its own (built-in) domestic hot water (DHW) preparation. To heat domestic hot water, the boiler therefore needs to be complemented with an external indirect-heated DHW tank (e.g. from the ATTACK Z-series - see the "How to connect" section below). This type of solution (boiler + separate tank) is common and proven especially where greater comfort of hot water draw-off at several points at once is required, since tank heaters can better cover even a temporarily higher DHW demand than instantaneous heating.

The ATTACK EKO COMBI range is the basic, entry-level line of ATTACK cast iron stationary boilers. It is intended for customers looking for a simple, reliable and affordable heating solution for a family house or smaller facility without unnecessary extras. EKO COMBI is built on the proven cast iron exchanger design and basic automation, making it one of the most accessible cast iron stationary gas boilers in the ATTACK range. It is a choice for those who expect above all functionality, long-term operational stability and low acquisition costs, and are willing to trade more advanced comfort features for a lower price.

Why a cast iron exchanger and not steel or aluminium?

When choosing a stationary gas boiler, customers often ask why they should opt for a cast iron exchanger when cheaper steel or lighter aluminium solutions are also available on the market. The answer is mainly related to the long-term durability of the material. Cast iron has higher thermal inertia than thin-walled steel, which in practice means a calmer, less "nervous" combustion process and less material stress during sudden changes in return water temperature (for example when starting up a cold system after a longer shutdown). Cast iron is also naturally more resistant to condensation corrosion, which can gradually damage thin-walled steel exchangers under an unsuitable operating regime (long-term low return water temperature).

Another practical argument is the already mentioned sectional (segmented) design. A cast iron exchanger is not made of a single piece but of several stacked sections joined by sealing gaskets. If one section were to become damaged during years of operation (which is unlikely even with cast iron, but theoretically possible, for example due to mechanical damage or extreme neglect of maintenance), a service technician can replace only the affected section without having to replace the entire boiler body. With one-piece steel or aluminium exchangers, this option usually does not exist, and damage to the exchanger means replacing the whole boiler or at least the entire exchanger block.

The disadvantage of cast iron is higher weight (see the approximate figure in the technical parameters table below) and a somewhat slower thermal response when starting from cold - however, for a stationary boiler intended for long-term, predominantly continuous operation (not frequent switching on/off as with a cottage used only a few times a year), these are rather marginal disadvantages compared to the benefit of a long service life and easier repairability.

Who this boiler is suitable for

The ATTACK EKO COMBI stationary cast iron boiler with an output of 25 kW is a suitable choice especially where a boiler room is available (it is not designed for wall mounting like common wall-hung combi boilers) and where a naturally draught chimney is available or planned. Typically this includes:

• Family houses with their own boiler room or utility room, where a long service life and easy serviceability of the appliance matter
• Larger buildings and multi-generational houses with higher heat consumption, where the robustness of the cast iron body is appreciated
• Smaller facilities, workshops, guesthouses or cottages with year-round or near year-round operation, where investing in a higher-quality body pays off through a longer service life
• Renovations replacing an older cast iron boiler where an existing chimney and gas piping sized for the given output are already available

On the other hand, if you are looking for a compact wall-hung solution for an apartment or smaller housing core, or a boiler with its own fast domestic hot water preparation without the need for a separate tank, a cast iron stationary COMBI boiler is probably not the best choice - in that case we recommend consulting with us about a more suitable alternative from ATTACK's wall-hung condensing boilers.

Key features

• Stationary (floor-standing) design with cast iron heat exchanger - high resistance to corrosion and thermal shock
• Nominal heat output 25 kW, fuel natural gas (LPG version on request/according to specific order specification)
• COMBI design = boiler without its own DHW preparation, intended to work together with an external indirect-heated tank (e.g. ATTACK Z-series)
• Sectional (segmented) cast iron exchanger - in case of damage allows replacement of a single section instead of the whole body
• Connection to a naturally draught chimney (atmospheric combustion)
• Robust construction suitable also for larger buildings and facilities with higher heating output requirements
• Basic, proven equipment without unnecessary extras - emphasis on simplicity and low acquisition price
• The delivery includes the boiler body itself including the burner and basic control - external DHW tank, circulation pump, expansion vessel, chimney accessories and room thermostat are not included in the base price unless explicitly stated

Technical parameters

Note: dimensions and weight are given as an approximate estimate based on the output category and typical construction of cast iron sectional boilers of this class - we recommend verifying the exact value for a specific unit in the manufacturer's current technical data sheet or directly with us before ordering, especially if you are planning exact construction preparation of a room or niche for the boiler.

How to connect: boiler + external DHW tank

Since this is a COMBI design without its own domestic hot water preparation, this boiler needs to be connected together with a separate (external) indirect-heated DHW tank. For this purpose, the ATTACK range offers the so-called Z-series of tanks (e.g. Z100PLUS, Z125PLUS, Z100NTR, Z125NTRA, Z160NTRA, Z125OKC, Z160OKC, Z200OKC and other versions including wall-hung horizontal OKCV variants) - we sell these tanks as a separate product, they are not included in the boiler's delivery or price.

For this output level (approx. 20-25 kW), we generally recommend a tank with a volume of 125-160 l, e.g. ATTACK Z 125 PLUS OKH NTR/HV, Z 125 OKC/NTR/HV or Z 160 OKC/NTR/HV (also available in wall-hung horizontal OKCV design, left/right) - a larger tank volume means more hot water "in reserve" for a sudden draw-off in several bathrooms at once.

The connection principle, in brief, is as follows: the boiler heats the heating (heat-carrying) water, which circulates both to the heating system (radiators, underfloor heating) and through the coil (exchanger) in the DHW tank, where it transfers heat to the domestic water. Switching between the heating circuit and heating the tank is usually handled by a three-way valve (in the ATTACK range e.g. models OT02 or OT44), controlled either by the boiler electronics or by a separate room thermostat/controller. The exact connection (piping route, placement of pumps, safety and mixing fittings) depends on the specific layout of the boiler room and on whether it is a simple two-pipe system or a more complex system with several heating circuits - we recommend having the final connection designed and carried out by an authorised heating/gas specialist who will also take into account locally applicable standards and regulations for connecting a gas appliance.

When ordering the boiler and the tank, we will be happy to help you choose a suitable combination of boiler output and tank volume according to the number of people in the household and the number of hot water draw-off points used simultaneously - do not hesitate to contact us before purchasing if you are unsure about the correct choice.

Maintenance and servicing in practice

As with any gas appliance, with the ATTACK stationary cast iron boiler regular servicing (usually once a year, carried out by an authorised service technician) is not only a condition for maintaining the warranty but above all a prerequisite for safe and economical operation. For cast iron boilers, servicing usually includes checking and, if necessary, cleaning soot and dust from the exchanger and burner, checking the tightness of the joints between individual sections, checking the chimney draught and flue path, and verifying correct combustion settings.

Compared to modern condensing boilers, maintenance of an atmospheric cast iron boiler is generally simpler and cheaper - for example, there is no need to worry about a condensate siphon or an exchanger sensitive to low return water temperature. On the other hand, it should be taken into account that atmospheric cast iron boilers of this design do not achieve the efficiency of the most modern condensing solutions, which is a common and fair trade-off between higher initial robustness/simplicity and the highest possible energy efficiency. If the lowest possible gas consumption at any cost is a decisive criterion for you, we will be happy to discuss alternatives from the ATTACK condensing range as well.

Frequently asked questions

1. Is domestic hot water (DHW) heating included in the price of this boiler?
No. This is a COMBI design without its own DHW preparation - the boiler only heats the heating water. To heat domestic hot water, an external indirect-heated tank (e.g. from the ATTACK Z-series) needs to be added, which is ordered and paid for separately.

2. Which DHW tank is suitable for a boiler with an output of 25 kW?
For this output level (approx. 20-25 kW), we generally recommend a tank with a volume of 125-160 l, e.g. ATTACK Z 125 PLUS OKH NTR/HV, Z 125 OKC/NTR/HV or Z 160 OKC/NTR/HV (also available in wall-hung horizontal OKCV design, left/right) - a larger tank volume means more hot water "in reserve" for a sudden draw-off in several bathrooms at once.

3. How does the EKO COMBI range differ from other ranges of the ATTACK COMBI cast iron offer (EKO, PLQ, KLQ, E, EZ)?
In short: it is the basic, entry-level range in the ATTACK cast iron boiler offer - simpler equipment, lower acquisition price, suitable for customers who prefer functionality and price over additional comfort.

4. What type of fuel is the boiler intended for, and can it be converted to a different fuel?
In its basic version, the boiler is designed for natural gas. An LPG (propane-butane) version is available on request/according to specific order specification - we recommend stating this requirement when ordering or inquiring with our sales team in advance.

5. What warranty does this boiler have?
ATTACK stationary gas boilers are covered by a 30-month warranty from commissioning, but no more than 36 months from the date of dispatch from the manufacturer's warehouse. An extended 5-year warranty applies to the cast iron exchanger body. The exact warranty conditions are governed by the warranty certificate supplied with the specific unit, and the prescribed commissioning conditions must be observed (usually by an authorised service technician).

6. Can the boiler be connected to an existing naturally draught chimney?
Yes, it is an atmospheric boiler designed for connection to a naturally draught chimney. The suitability of a specific chimney (diameter, height, material) needs to be assessed individually, ideally during an on-site inspection or in cooperation with a chimney sweep/inspection technician, especially if the boiler is being connected to an older masonry chimney.

7. Can the boiler be connected to a system with several heating circuits (e.g. radiators + underfloor heating)?
Yes, combining several circuits with different heating water temperatures is common - however, it requires adding a mixing circuit with its own pump and control (in the ATTACK range e.g. sets DPP25007/DPP25008 or ESBE versions DPP25020-DPP25022). We recommend consulting the connection design with a heating engineer or directly with our team.

8. Can the boiler be ordered without a DHW tank, as just the body itself?
Yes - this product represents the boiler body itself. The DHW tank, circulation pump, chimney accessories, three-way valve and room thermostat/controller are ordered as separate items according to the needs of the specific installation - we will be happy to prepare a complete list of the accessories needed, tailored to your project.

9. What is the difference between this atmospheric cast iron boiler and a modern condensing boiler?
An atmospheric cast iron boiler operates with a higher flue gas temperature and does not use condensation of water vapour from the flue gases for additional heat gain, so its efficiency does not reach the values of modern condensing boilers. In return, it offers a simpler construction, lower sensitivity to the return heating water temperature and generally simpler, cheaper maintenance without the need to deal with condensate drainage. The choice between a cast iron atmospheric and a condensing solution is always a trade-off between initial robustness/simplicity and the highest achievable efficiency - we will be happy to help you weigh both directions according to your priorities.

10. Where can I order the boiler and how does delivery work?
You can order the boiler directly through the atria.sk e-shop. When ordering, we also recommend considering the order of a suitable DHW tank from the Z-series and any additional accessories (chimney parts, three-way valve, circulation pump, room thermostat) at the same time, so that you have a complete solution ready for installation. If you are unsure about choosing the combination of boiler + tank + accessories, do not hesitate to contact us before ordering - we will be happy to advise you so that you do not order something you will not ultimately need, or conversely, so that nothing essential is missing.

Warranty and service

ATTACK EKO COMBI stationary cast iron gas boilers are covered by a standard warranty of 30 months from commissioning of the boiler, but no more than 36 months from the date of dispatch from the manufacturer's warehouse (whichever period occurs first). The manufacturer provides an extended 5-year warranty on the cast iron exchanger body itself. To claim the full warranty period, the commissioning conditions specified by the manufacturer must be observed (usually by a qualified service technician authorised for this activity) and a proper service book/warranty certificate must be kept. If you have any questions about the warranty, servicing or choosing suitable accessories (DHW tank, circulation pump, chimney parts, control), do not hesitate to contact us - we will be happy to help you choose and order a complete solution tailored to your needs.