ATTACK 25 PLQ COMBI - stationary gas cast iron boiler 20-25 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-proven heating solutions on the market. Cast iron as an exchanger material is highly resistant to corrosion and thermal shock, and it tolerates a less gentle operating regime (frequent cycling, 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 - the 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 entire exchanger. In the long run, this can mean lower servicing costs compared to single-piece exchangers. The stationary design (a boiler standing on the floor, not wall-mounted) also simplifies installation at higher outputs and facilitates connection to a natural-draught chimney, which is commonly used in both older and newer boiler rooms.

The model you are currently viewing belongs to the ATTACK PLQ COMBI range and is designed for a rated heat output of 20-25 kW. It is a stationary gas boiler in the COMBI version - in the context of this cast-iron ATTACK 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 must therefore be complemented with an external indirect-heated DHW storage tank (e.g. from the ATTACK Z-series - see the "How to connect" section below). This type of solution (boiler + separate storage tank) is common and proven, especially where greater comfort is required for hot water draw-off at several points of use at the same time, since storage water heaters can cover even temporarily higher DHW consumption better than instantaneous heating.

The ATTACK PLQ COMBI range is positioned one level above the basic EKO COMBI range. Compared to it, it offers somewhat more comfortable operation and generally also a wider output modulation range (the boiler can work within the range stated in the product name, not just at a single fixed value), which in practice results in smoother adaptation of output to the current heat loss of the building and somewhat more economical operation during transitional periods (spring, autumn). PLQ COMBI is a suitable choice for customers who want a slight upgrade over the most basic range while still staying at a reasonable price level.

Why a cast-iron exchanger and not a steel or aluminium one?

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 lower material stress during sudden changes in return water temperature (for example, when a cold system starts up after a longer shutdown). At the same time, cast iron is naturally more resistant to condensation corrosion, which, under an unsuitable operating regime (a permanently low return water temperature), can gradually damage thin-walled steel exchangers.

Another practical argument is the already mentioned sectional (segmented) construction. A cast-iron exchanger is not made of a single piece, but of several sections stacked on top of each other and joined by sealing gaskets. If one section were to be damaged over the 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 single-piece steel or aluminium exchangers, this option usually does not exist, and damage to the exchanger means replacing the entire boiler or at least the entire exchanger block.

The disadvantage of cast iron is its higher weight (see the indicative figure in the technical parameters table below) and a somewhat slower thermal response when starting up from cold - however, for a stationary boiler intended for long-term, mostly 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 is this boiler suitable for

The ATTACK PLQ COMBI stationary cast-iron boiler with an output of 20-25 kW is a suitable choice especially where a boiler room is available (it is not intended for wall mounting like ordinary wall-mounted combi boilers) and where a natural-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 nearly year-round operation, where the investment in a higher-quality body pays off through a longer service life
• Renovations, where an older cast-iron boiler is being replaced and an existing chimney and gas supply sized for the given output are available

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

Key features

• Stationary (floor-standing) design with a cast-iron heat exchanger - high resistance to corrosion and thermal shock
• Rated heat output of 20-25 kW, fuel: natural gas (LPG version available on request/depending on the specific order specification)
• COMBI version = boiler without its own DHW preparation, designed to work together with an external indirect-heated storage tank (e.g. ATTACK Z-series)
• Sectional (segmented) cast-iron exchanger - in case of damage, allows replacement of an individual section instead of the entire body
• Connection to a natural-draught chimney (atmospheric combustion)
• Robust construction suitable even for larger buildings and facilities with higher heating output demands
• Wider output modulation range within the stated kW range - smoother adaptation to the building's heat loss
• The delivery includes the boiler body itself, including the burner and basic control - the external DHW storage tank, circulation pump, expansion vessel, chimney accessories and room thermostat are not included in the basic price unless explicitly stated

Technical parameters

Note: dimensions and weight are stated as an indicative estimate based on the output category and the standard 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 precise construction preparation of a room or niche for the boiler.

How to connect: boiler + external DHW storage tank

Because this is a COMBI version without its own domestic hot water preparation, this boiler needs to be connected together with a separate (external) indirect-heated DHW storage tank. For this purpose, ATTACK offers the so-called Z-series of storage tanks (e.g. Z100PLUS, Z125PLUS, Z100NTR, Z125NTRA, Z160NTRA, Z125OKC, Z160OKC, Z200OKC and other versions, including horizontal wall-mounted OKCV variants) - we sell these storage 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 storage tank with a capacity 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 a horizontal wall-mounted OKCV design, left/right) - a larger storage tank capacity means more hot water "in reserve" for a sudden draw-off in several bathrooms at once.

The connection principle is briefly as follows: the boiler heats the heating (heat transfer) water, which circulates both into the heating system (radiators, underfloor heating) and through the exchanger (coil) in the DHW storage tank, where it transfers heat to the domestic water. Switching between the heating circuit and heating the storage tank is usually handled by a three-way valve (in the ATTACK range, e.g. the OT02 or OT44 models), controlled either by the boiler's electronics or by a separate room thermostat/controller. The exact connection (piping layout, 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 engineer, who will also take into account the locally applicable standards and regulations for connecting a gas appliance.

When ordering the boiler and the storage tank, we will be happy to help you choose a suitable combination of boiler output and storage tank capacity based on the number of people in the household and the number of hot water draw-off points used simultaneously - please 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, a regular service inspection (usually once a year, carried out by an authorised service technician) of the ATTACK stationary cast-iron boiler 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 the exchanger and burner of soot and dust, checking the tightness of the joints between the individual sections, checking the chimney draught and the flue gas path, and verifying the 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 take care of 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 construction 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 the decisive criterion for you, we will be happy to discuss alternatives from the ATTACK condensing range with you as well.

Frequently asked questions

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

2. Which DHW storage tank is suitable for a boiler with an output of 20-25 kW?
For this output level (approx. 20-25 kW), we generally recommend a storage tank with a capacity 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 a horizontal wall-mounted OKCV design, left/right) - a larger storage tank capacity means more hot water "in reserve" for a sudden draw-off in several bathrooms at once.

3. How does the PLQ COMBI range differ from the other ranges in the ATTACK COMBI cast-iron lineup (EKO, PLQ, KLQ, E, EZ)?
In short: compared to the basic EKO COMBI range, it generally offers a wider output modulation range within the stated kW range, which can result in smoother adaptation of the output to the current heat demand.

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

5. What is the warranty on this boiler?
ATTACK stationary gas boilers are covered by a warranty of 30 months from commissioning, but no more than 36 months from the date of shipment 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 attached to the specific unit, and the prescribed commissioning conditions must be observed (usually by a qualified service technician).

6. Can the boiler be connected to an existing natural-draught chimney?
Yes, this is an atmospheric boiler designed for connection to a natural-draught chimney. The suitability of a specific chimney (diameter, height, material) needs to be assessed individually, ideally during a site visit 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. the DPP25007/DPP25008 sets or ESBE versions DPP25020-DPP25022). We recommend discussing the connection design with a heating engineer/designer or directly with our team.

8. Can the boiler be ordered without a DHW storage tank, just the body itself?
Yes - this product represents the boiler body itself. The DHW storage 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 to gain additional heat, which is why its efficiency does not reach the values of modern condensing boilers. In exchange, 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 options 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 recommend also considering ordering a suitable DHW storage tank from the Z-series and any other necessary 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 right combination of boiler + storage tank + accessories, do not hesitate to contact us before ordering - we will be happy to advise you so that you don't order something you won't ultimately need, or, conversely, so that nothing essential is missing.

Warranty and service

ATTACK PLQ 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 shipment 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 set by the manufacturer must be met (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 storage tank, circulation pump, chimney parts, controls), please do not hesitate to contact us - we will be happy to help you choose and order a complete solution tailored to your needs.