ATTACK Boiler Conversion Kit 25-35 SLX to COMBI Pellet with 30 kW Burner

Product detailed description

ATTACK Conversion Kit for 25-35 SLX Boiler to COMBI Pellet with 30 kW Burner

The SL20968 kit allows for the additional conversion of the ATTACK 20-35 SLX Profi wood gasification boiler to fully automatic operation burning wood pellets. This is a proven solution for households that want to keep the benefits of the massive and durable cast-iron/steel ATTACK SLX Profi boiler body, while also gaining the comfort of automatic feeding without the daily operation typical of wood-fired boilers.

The kit includes a pellet burner with a power output of 30 kW, a pellet storage tank, a fuel transport system (feeding system/hose depending on the specific storage tank design) and burner control electronics including connection to the existing boiler control. After the conversion, the boiler can be operated either exclusively on pellets, or in combined mode, where the original possibility of feeding wood as a backup fuel is also retained (for example in case of a pellet supply outage or power failure).

Compatibility

The SL20968 kit is intended exclusively for ATTACK 20-35 SLX Profi series boilers. Before ordering the kit, it is necessary to report the boiler serial number to which the kit will be fitted – based on the serial number, an ATTACK service technician will verify the exact boiler design (loading chamber dimensions, door type, control revision) and prepare the corresponding components and mounting accessories. Installation of a combination of burner and boiler other than the specified one is not possible and could lead to incorrect combustion function or void the warranty.

How pellet combustion works in a converted boiler

After converting the 20-35 SLX Profi boiler using the SL20968 kit, the pellet burner takes over fuel supply and ignition. The burner automatically feeds a precise amount of pellets from the storage tank into the combustion chamber via the feeding system (screw conveyor or pneumatic feeder depending on the specific storage tank design); the pellets are ignited by a glow coil and burned with precisely controlled air supply. The burner's control electronics continuously evaluate the required output based on the heating water temperature or room thermostat and smoothly adjust the amount of pellets fed as well as the intensity of combustion air. As a result, the boiler works with high efficiency even under partial load, unlike manual wood heating, where output control depends on the operator and the manner of fuel feeding.

Automatic pellet operation brings a fundamental difference in operating comfort compared to wood heating. While with a wood gasification boiler fuel must be added manually (usually 1–2 times a day depending on frost and hopper volume), with pellet operation it is enough to periodically refill the pellet storage tank, with the interval between refills depending on the volume of the chosen tank and current consumption – with larger tanks this can be a matter of weeks of operation without the need for operator intervention. This will be especially appreciated by households where it is not possible to add fuel during the day (working owners, cottages visited only on weekends, elderly people who cannot physically handle heavy wood logs).

Comparison of wood and pellet heating

The decision between keeping the boiler running on wood and converting to pellets depends on several factors. Wood is generally a cheaper fuel per unit of heat produced, especially if the household has its own or a cheap source of firewood, but it requires physical work with feeding, storage and preparation (cutting, splitting, drying). Pellets, on the other hand, are more expensive per unit of heat, but eliminate the work of feeding, simplify storage (bags or a large-volume tank instead of space for wood) and allow more precise output control thanks to automatic dosing. Combined operation after installing the SL20968 kit allows you to benefit from both fuels according to the current situation – for example heating with wood when an operator is present and has access to cheap wood, and switching to automatic pellet operation during absence, holidays or in periods when wood is not conveniently available.

Storage and refilling of pellets

Wood pellets must be stored in a dry environment protected from moisture – moisture causes pellets to break down and deteriorate, losing their calorific value and potentially clogging the burner's feeding system. The storage tank supplied as part of the SL20968 kit can be refilled manually (with bagged pellets) or, in some designs, connected to a larger external tank/silo to extend the interval between refills. We recommend choosing the tank volume according to the actual annual heat consumption of the building and the available space in the boiler room – when designing the tank capacity, an ATTACK sales or service representative will be happy to advise.

Compatibility with existing boiler control

One of the main advantages of the SL20968 kit is the connection of the pellet burner's control unit with the original control of the ATTACK 20-35 SLX Profi boiler via a connecting cable supplied with the kit. Thanks to this, there is no need to change or add to the existing wiring of the heating system – the circulation pump, mixing circuit and any room thermostat can continue to work in the same configuration as before the conversion, the burner's control unit only takes over the function of switching and controlling the output of the heat source. The service technician will also check and, if necessary, reprogram the parameters of the original boiler control during installation so that the cooperation of both units proceeds without conflicts (for example in controlling the circulation pump or signalling fault states).

Key features of the SL20968 kit

Why converting to pellets makes sense

• Automatic operation – the burner feeds pellets from the storage tank automatically according to the control system's demand, without the need for daily wood feeding.
• Preservation of the original boiler body – there is no need to replace the entire boiler, which saves costs compared to buying a new pellet boiler.
• Possibility of combined wood/pellet operation – you can switch between automatic pellet combustion and manual wood feeding as needed.
• Suitable for both cottage owners and year-round living – it will be appreciated especially by households that want to reduce the physical demands of heating with wood, but do not want to give up the possibility of heating with wood when it is available.
• Controlled regulation of burner output according to current heat demand, which reduces pellet consumption compared to unregulated operation.

Technical data of the SL20968 kit

Detailed composition of the SL20968 kit

The conversion kit is supplied as a complete set, which includes primarily the pellet burner itself with an output of 30 kW with a built-in ignition element (glow coil), the burner's control unit with its own display and the ability to set operating parameters (output levels, cleaning cycles, time schedules), a pellet storage tank including a lid and a fuel level sensor, a feeding system (screw conveyor or hose feeder depending on the chosen design) and the mounting accessories needed to fit the burner into the door or loading section of the boiler. The delivery also includes a connecting cable between the burner's control unit and the original boiler control, which ensures that both devices work together as one functional unit.

Servicing and maintenance of the burner

A pellet burner requires significantly less regular operation than classic wood feeding, but it is not entirely maintenance-free. We recommend regularly (according to the operating manual, usually once every few weeks of operation) checking and cleaning the burner's combustion bowl of residual ash, which, if not cleaned sufficiently, can restrict the supply of combustion air and reduce combustion quality. At least once a year before the heating season, we recommend having a service inspection of the burner performed by an authorized ATTACK technician, who will check the functionality of the ignition element, the tightness of the feeding system, the control settings and, if necessary, perform combustion calibration. Regular servicing extends the burner's service life and maintains the declared efficiency and low emissions of operation.

Economics and ecology of pellet operation

Wood pellets are among the renewable energy sources, usually produced from waste wood material (sawdust, shavings) by compression under high pressure without the addition of chemical binders. Burning pellets in a controlled burner with the SL20968 kit is therefore considered an ecologically favourable way of heating with a low ash content and low emissions compared to uncontrolled wood combustion. From an economic point of view, the cost of heat from pellets is usually higher than from cheap own wood, but lower than or comparable to heating with electricity or gas, with significantly higher operating comfort. We recommend assessing the exact return on investment in the conversion kit individually, based on current fuel prices and the previous heating method of the specific household.

Installation and commissioning

Installation of the SL20968 kit, including connection to the existing boiler, setting of the burner control and initial commissioning must be performed exclusively by an authorized ATTACK service technician. During installation, the burner is installed into the loading or combustion section of the boiler according to the manufacturer's installation instructions, and it is also connected to the existing chimney draught and the electrical network. It is also necessary to continue to comply with the recommendations valid for the original boiler – especially protection against low-temperature corrosion using a mixing circuit (min. 60 °C return temperature) and ideally the addition of a buffer tank, which evens out fluctuations in heat demand.

Before the actual installation, we also recommend considering the placement of the pellet storage tank in the boiler room so that comfortable access is ensured when refilling it (for example close to the boiler room door or window when delivering bagged pellets). When planning the space, it is also advisable to allow for a reserve for a possible later extension with an external tank of larger volume, should future consumption or requirements for operating comfort increase.

Frequently Asked Questions

Is it necessary to state the boiler serial number when ordering?
Yes, the boiler serial number is necessary to verify exact compatibility and to prepare the correct mounting components of the SL20968 kit.

Can I still heat with wood after the conversion?
In most designs, yes – the boiler can be operated in combined wood/pellet mode according to current need and fuel availability.

Who can install the kit?
Installation and commissioning may only be performed by an authorized ATTACK service technician, which is also a condition for maintaining the warranty on both the boiler and the kit.

What type of pellets is suitable for the SL20968 kit burner?
We recommend high-quality certified wood pellets (e.g. ENplus A1) with a low dust and ash content, which extends the burner's service life and reduces the need for cleaning.

Will the conversion affect the boiler warranty?
Installation must be performed by an authorized service according to the prescribed procedure, so as not to affect the warranty of the boiler body. The original warranty conditions for the boiler (36 months from commissioning, or an extended 7-year warranty with protection against low-temperature corrosion) remain valid even after the conversion, provided the operating conditions continue to be observed.

Is a buffer tank necessary even during pellet operation?
A buffer tank is not as necessary during automatic pellet operation as it is with wood heating, but it still brings benefits in evening out heat demand and reducing the number of burner switching cycles.

Can the kit be moved to a different boiler later?
The SL20968 kit is manufactured and set up specifically for a particular boiler series (20-35 SLX Profi) and in some cases even for a specific boiler serial number. Moving it to a different boiler type is not possible without the intervention of an ATTACK service technician, or would require adapting the mounting components.

How often does the pellet storage tank need to be refilled?
The refilling interval depends on the chosen tank volume, the output at which the burner operates, and the heat loss of the heated building. With larger tanks, refilling every few days to weeks is common, but the exact interval will only be established by each household after the first season of actual operation.

Does the burner make noise during operation?
The pellet burner hums slightly during dosing and combustion (fan, feeding system), but the noise level is comparable to common automatic heating technologies and, with correct placement in the boiler room, does not present a problem for the household.

What happens in the event of a power failure?
Both the pellet burner and the feeding system require electricity to operate, so in the event of a power outage the burner will automatically stop dosing and burning fuel. If the boiler was left in combined mode, it is possible to temporarily switch to manual wood heating; for critical buildings we recommend considering a backup power supply (UPS) at least for the control electronics and the circulation pump.

Related ATTACK boilers to which the SL20968 kit can be fitted

The SL20968 kit is intended for boilers from the range of ATTACK 20-35 SLX Profi wood gasification boilers, which you can find in the same category of the e-shop (Stationary boilers and tanks > Classic and gasification boilers > Attack). When choosing a specific boiler model, we recommend taking into account the calculated heat loss of the building and then choosing the corresponding output within the given range, to which this conversion kit is fully compatible.

If you are still choosing a specific boiler and are considering a conversion to pellets already at the time of purchase, we recommend consulting this information directly with an ATTACK sales representative – some revisions of the boiler body and door may have slightly different dimensions suitable for fitting the burner, so it is advisable to plan any future conversion already when choosing a specific model and its output range.

Warranty

The SL20968 kit is covered by a warranty according to the general warranty terms of the manufacturer ATTACK, s.r.o. The boiler to which the kit is fitted retains the original warranty conditions valid for SLX Profi gasification boilers – standard 36 months from commissioning (max. 42 months from dispatch), with the possibility of an extended 7-year warranty on the boiler body with permanently ensured protection against low-temperature corrosion (mixing circuit min. 60 °C). Exact conditions can be found in the warranty certificate supplied with the kit and the boiler.