Installation of Attack Electric Electric Boiler: Procedure, Requirements, and Connection

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Installation of the Attack Electric electric boiler: complete procedure, requirements and connection

The Attack Electric electric boiler is among the technically less demanding heating solutions compared to gas or solid fuel boilers – there is no combustion chamber, no chimney, no fuel supply. Despite this, proper installation has a number of precise requirements, and if someone underestimates them, it usually ends either in boiler failure or problems with the electrical installation. In this article, I will go through the entire installation process from the preparation of the building to the first start-up – including specific dimensions, electrical parameters and common errors I have encountered in my professional practice.

Where the boiler can be placed: space and construction requirements

The first thing to resolve before ordering the boiler is the installation location. Unlike gas boilers, the Attack Electric electric boiler does not require an air supply for combustion or exhaust of combustion gases. This significantly expands the choice of rooms – it can be placed in a boiler room, technical room, in a hallway, in a bathroom (if protection against moisture is provided), or even in a storage room.

Practical minimum space requirements vary according to the specific model, but the following general rules apply:

Minimum distance from side walls: at least 50 mm (ideally 100 mm) for handling covers and possible service
Minimum distance in front of the boiler: at least 600 mm to allow operation of the display and access to the hydronic part
Minimum distance above the boiler: at least 300 mm
The boiler must not be installed in a space where freezing is a risk – water in the system would freeze
The space must be dry, protected from direct splashing water (IPX4 minimum for a bathroom)

Wall load capacity is also important, as some models are wall-mounted. For example, the Attack Electric Easy 8 is a compact wall-mounted unit that requires a solid masonry or drywall wall with anchor plugs corresponding to the weight of the full boiler including water in the circuit (typically 5–12 kg depending on the water content size).

Hydraulic connection: schematic, connections and fittings

The hydraulic installation is as important to the heating technician as the electrical one. An electric boiler is simpler than a gas boiler, but it still works with a closed water system under pressure, and any error in the hydraulics will show up – either as reduced efficiency or as a boiler protection fault.

Basic hydraulic connections

Attack Electric boilers have the following standard hydraulic connections:

Outlet (flow/supply to the system): G 3/4" or G 1" depending on the model and power
Inlet (return/return from the system): the same size as the outlet
Pressure relief valve: typically pre-mounted by the manufacturer, the discharge must be directed to the drain
Drain valve: at the lowest point of the circuit
Air vent: at the highest point of each branch

For higher power models, such as Attack Electric Excellent 15 kW or Attack Electric Excellent 24, 22 kW, the water flow through the boiler is higher and the distribution piping must be dimensioned accordingly – at least DN 22 (3/4") for 15 kW, at least DN 28 (1") for 24 kW.

Expansion tank and safety valve

A closed heating system must have a properly pre-dimensioned expansion tank. Standard rule: expansion tank volume = water volume in the system × 0.1 (for systems up to 70°C). So if you have 80 liters of water in the system, you need at least an 8-liter expansion tank, in practice a reserve is added and 12 or 18 liters are chosen.

The safety valve must be set to a pressure that does not exceed the maximum working pressure of the boiler (usually 3 bar). The discharge of the safety valve must be directed to the drain – not just into the air in the boiler room. I have seen installations where the discharge was directed to the pipe insulation, which caused damage when the valve opened.

Circulation pump

Some Attack Electric models have an integrated circulation pump (e.g. the Excellent series), others (simpler versions) require an external pump. Always check the technical documentation of the specific model. If the pump is external, it must be controlled by the boiler – that is, connected to the pump output on the control board, not just switched by phase from the grid.

Electrical connection: power, fusing and cabling

This is the most sensitive part of the entire installation. An electric boiler is a high-power appliance and must be installed by an electrician with the appropriate qualifications. Below are the specific parameters necessary for correct dimensioning:

Power supply and power – what you need to know before installation

All Attack Electric models with a power of over approximately 3.5 kW are three-phase (400V / 3N~50Hz). Single-phase connection (230V) is only possible exceptionally for the smallest power outputs, where the manufacturer explicitly states this. For clarity:

Attack Electric Easy 8 – power 8 kW, three-phase, current approx. 11.6 A per phase
Attack Electric Excellent 8/7.5 kW – power 8 kW (or 7.5 kW), three-phase
Attack Electric Excellent 15 kW – power 15 kW, three-phase, current approx. 21.7 A per phase
Attack Electric Excellent 24/22 kW – power up to 24 kW, three-phase, current approx. 34.6 A per phase

Therefore, before purchasing the boiler, check with your electricity distributor what your contracted power is and whether three-phase connection is possible. In older apartment buildings with single-phase connections, this can be a problem – you will need a tariff change agreement or a new connection.

Cable and fuse dimensioning

The cable must be dimensioned for continuous current with a reserve. A simple formula applies: I = P / (U × √3 × cos φ). For cos φ = 1 (pure resistive load – electric heating) this is directly P/(U×√3).

Specific recommendations for individual power outputs:

Up to 8 kW: cable CYKY 5×2.5 mm², fuse B16A (three-phase)
Up to 12 kW: cable CYKY 5×4 mm², fuse B20A (three-phase)
Up to 15 kW: cable CYKY 5×4 mm² or 5×6 mm², fuse B25A (three-phase)
Up to 24 kW: cable CYKY 5×10 mm², fuse B40A (three-phase)

The cable must run in a separate circuit directly from the distribution board. No extensions, no branches. The length of the cable also increases resistance – for a cable longer than 20 meters, it is necessary to switch to a larger cross-section (e.g. from 4 mm² to 6 mm²) due to voltage drop.

Protective devices: residual current device and overvoltage protection

In addition to fuses, the boiler circuit must include:

Residual current device (RCD): type A or B (depending on the boiler's control electronics), sensitivity 30 mA – protects against electric shock
Overvoltage protection (SPD): class C or combination B+C – especially important in areas with storm activity and long external supplies
Main switch: located near the boiler, easily accessible, so it can be disconnected quickly if necessary

Earthing (PE) is mandatory and must have a resistance below 4 Ω (ideally below 1 Ω). In the reconstruction of old houses, it often happens that the earthing system is negligible – this must be resolved before installing the boiler.

Installation step by step

We will now go through the entire installation process step by step, as it would be carried out by an experienced installer. This procedure assumes that the electrical part is carried out by a qualified electrician and the hydraulic part by a heating engineer or installer with appropriate experience.

Step 1: Preparation and checking the base

Check the strength of the wall or floor (depending on the mounting method). For wall-mounted models, mark the position of the mounting points according to the template or installation dimensions from the manual. Make sure there are no electrical conduits or pipes running in the drilling area – use a detector.

Step 2: Mechanical installation of the boiler

Mount or place the boiler in its position. Check the level (using a spirit level) – the boiler must stand straight so that the air vent works properly and any condensate (if any) can be drained. Tightened mounting hooks or legs must be stable – the boiler must not move.

Step 3: Hydraulic connection

Connect the hydraulic connections in the following order:

Install ball valves on the inlet and outlet – they allow the boiler to be disconnected without emptying the entire system
Install a safety valve (if not pre-mounted) and a discharge to the drain
Connect the expansion tank to the return pipe (before the circulation pump)
Connect the boiler to the heating system (supply and return pipes)
Install a drain valve at the lowest point of the system
Install an automatic air vent at the highest point of each branch

All connections must be sealed – either with Teflon tape (PTFE), hemp fibers with sealant, or compression fittings. Never use dry threaded connections without sealing.

Step 4: Filling and air venting the system

Before filling the system, check that all air vents and drain valves are closed. Slowly open the cold water supply (or fill manually with a hand pump from a filling kit). Monitor the pressure gauge – the system should be filled to a cold pressure of 1.0–1.5 bar. Then gradually vent each radiator and branch of the system. After venting, check the pressure again and adjust.

Important: the water in the system must meet the manufacturer's requirements for hardness. Water that is too hard (over 300 mg/l CaCO₃) forms limescale on the boiler's heating elements and shortens their lifespan. If you have hard water (which is common, for example, in the Žitný ostrov area or in limestone regions), use a water softener or corrosion inhibitor.

Step 5: Electrical connection

The electrical part must be carried out by an electrician with the appropriate qualification. Procedure:

Disconnect the entire distribution board from the power supply (via the fuse at the meter)
Route the cable from the distribution board to the boiler in protected channels or conduits
Install a fuse and residual current device for the boiler circuit in the distribution board
Install the main boiler switch near the device
Connect the supply cable to the boiler's terminal block according to the diagram in the manual (L1, L2, L3, N, PE)
Check the correctness of the connection and tighten all terminals to the torque specified in the manual

When working with the Attack Electric Excellent 8/7,5 kW, the terminal block is usually accessible after removing the front cover – be careful not to damage the sealing or the display cables when removing it.

Step 6: Connecting external sensors and control

Attack Electric Excellent boilers have multiple inputs for external sensors and control:

External temperature sensor (NTC) – for equithermal control
Input for an external room thermostat or OpenTherm controller
Input for the TÚV tank sensor – if you are using TÚV Module Set (TÚV preparation in an external tank)
Output for controlling an external pump
Output for a TÚV three-way valve

These sensors are connected to the low-voltage terminal block of the control board (typically 12–24V DC or contactless inputs). Sensor wiring runs separately from power cables – a minimum distance of 100 mm is required to avoid inductive interference.

Step 7: First start-up and setup

Before the first switch-on, check the entire procedure:

System pressure 1.0–1.5 bar (cold)
System is bled of air
All hydraulic connections visually free of leaks
Electrical connections checked, insulation resistance measured by an electrician
Main switch in the OFF position

Then switch on the main switch and the electricity from the distribution board. The boiler will boot up and the display will activate. Set the basic parameters (supply temperature, TÚV temperature if applicable, and time program) according to the manual. Manually start the circulation pump (via the service menu) and check the flow. Only after that, start the heating.

During the first heating cycle, monitor the system – check for water leaks from the hydraulics and whether the boiler stops due to an error message. After reaching operating temperature, bleed the system again (air is released from the system during heating).

Special considerations when installing with TÚV accessories

If you want to provide hot water (TÚV), an external tank and accessories are required. Attack Electric Excellent boilers natively support this via the tank sensor input and the three-way valve output.

This solution requires the TÚV Module Set (TÚV preparation in an external tank), which includes a three-way switching valve and necessary accessories. The hydraulic diagram changes: the boiler now has two circuits – heating and the TÚV tank circuit. The three-way valve switches according to priority (usually TÚV has priority over heating).

When installing the TÚV circuit, the following rules apply:

The TÚV tank must be equipped with a safety valve set to the maximum tank pressure (usually 6 bar) with the exhaust directed to a drain
Install a check valve on the cold water supply to the tank to prevent hot water from returning to the cold water system
Connect the tank temperature sensor (NTC) according to the boiler diagram to the appropriate terminals on the control board
Place the tank as close as possible to the boiler – this minimizes heat loss in the piping between the boiler and the tank
With a 15 kW boiler and a 200-liter tank, the boiler can heat cold water (15°C) to 55°C in approximately 80–90 minutes – this is a real time, not marketing

More details about the operation of this configuration can be found in the topic TÚV Module for Electric Boiler: How Hot Water Preparation Works in an External Tank? in the Knowledge Center.

Common installation errors – from practice

From decades of customer experience with electric boilers, I know that the same errors repeat themselves. Here are the most common ones:

Undersized cable: The customer has a 15 kW boiler, but uses a 2.5 mm² cable. At full power, the cable overheats, the circuit breaker trips, and in the worst case, the cable insulation is damaged. Result: the entire cabling must be replaced.
Missing residual current device (RCD): Some electricians argue that a circuit breaker is sufficient. It is not – RCD 30 mA is mandatory according to STN 33 2000.
Improperly oriented safety valve: The exhaust points toward the electrical part of the boiler or into an enclosed space. When the valve opens, it causes damage.
Air in the system after start-up: Insufficient bleeding during installation. The boiler reports a flow error or operates noisily. Solution: thorough bleeding at operating temperature.
Incorrectly set expansion tank: Either missing or with incorrect pre-pressure. Result: the safety valve regularly opens (drips) or the system lacks sufficient compensating volume.
Missing ball valves on the boiler: When service is required, the entire system must be drained. Two extra minutes during installation will save hours of work during service.
External sensor on a sunny side or in a garage: The equithermal control works poorly, and the boiler behaves unpredictably. The external sensor should be placed on the north side of the house, protected from direct sunlight and precipitation.

Inspection and handover of the installation

After completing the installation, the following checks and documentation must be carried out:

Electrical inspection: An electrician must issue a report on the professional inspection and test (inspection report) according to STN 33 2000-6. Without it, the installation is not legal and insurance may not cover any damage.
Commissioning protocol: The manufacturer or authorized service will issue a protocol of the first start-up – some warranties are conditional on this document.
Pressure test: The hydraulic installation should be pressure tested at 1.5 times the working pressure before backfilling or covering (minimum 4.5 bar for systems with a working pressure of 3 bar).
Operator training: The customer must know how to turn the boiler on and off, set the temperature, and how to respond to error messages. I recommend providing a physical manual and also referring to the topic Regulation and setting of the Attack Electric boiler: how to save on electricity?.

Service and warranty requirements

Attack Electric boilers have a standard warranty period, which can be extended by registering the product and commissioning it with an authorized service. Warranty conditions typically include:

Installation must be carried out according to the manufacturer's installation instructions
Electrical installation must be carried out by a qualified electrician
Water quality in the system must meet the manufacturer's requirements
Regular maintenance must be carried out according to the service plan (more in the topic Maintenance and service of the Attack Electric boiler: what and when to check?)

Frequently asked questions (FAQ)

Can I install the Attack Electric boiler myself, without a professional?

You can handle the hydraulic part yourself if you have sufficient experience, but not the electrical part. Act No. 124/2006 Coll. and related STN standards clearly state that work on electrical installations with a voltage above 50V AC may only be performed by a person with the appropriate electrical qualification (at least §21 of Government Regulation No. 508/2009 Coll.). Moreover, without an electrical inspection, the installation is not legal and you may have problems with insurance in case of damage.

What water should be used for filling the heating system?

Ideal is water with hardness below 200 mg/l CaCO₃ (hardness level up to 2). If you have harder water (which is common in Slovakia, especially in the southwest regions), it is advisable to use a water softener or a corrosion and scale inhibitor doser. The manufacturer usually specifies the maximum acceptable hardness in warranty conditions – respect it.

What pressure should be in the system for Attack Electric boilers?

The cold filling pressure (without heating) should be 1.0 to 1.5 bar. At operating temperature (50–70°C), the pressure increases by 0.3–0.5 bar – i.e., to 1.3–2.0 bar. The maximum allowable operating pressure of the boiler is typically 3 bar – the safety valve opens when exceeded. If the safety valve regularly drips, the expansion tank is either undersized or has an incorrect pre-pressure.

Is it necessary to notify the electricity distributor about the installation of an electric boiler?

Yes, when changing the power or tariff. If your boiler increases the total power of the household beyond the current contract with ZSE/SSE/VSE, you must request a contract change and possibly a new tariff. Many households switching to an electric boiler request a two-tariff tariff (HDO), where the boiler is operated during the cheaper night tariff. More about this aspect can be found in the topic Regulation and setting of the Attack Electric boiler: how to save on electricity?.

Can I connect underfloor heating and radiators to the electric boiler at the same time?

Yes, but it requires hydraulic separation into two branches with different temperature parameters. Underfloor heating operates with a supply temperature of 35–45°C, radiators at 60–75°C. A solution is a three-way mixing valve on the underfloor heating branch, which mixes hot boiler water with return water to the required low temperature. The boiler thus operates at a higher temperature difference for radiators and the underfloor heating branch is limited by a valve.

What to do if the boiler does not start immediately after the first switch-on?

First, check the display – the boiler usually shows an error code. Most common causes: low pressure in the system (add water), air in the system (bleed it), flow error (check if the circulation pump is working and ball valves are open). If a temperature sensor error is displayed, check the wiring of the sensors. An overview of error codes is in the topic Common faults of Attack Electric boilers and how to solve them.

Conclusion: good installation is the basis for the long life of the boiler

The Attack Electric electric boiler is a technologically reliable device that works for many years without significant problems when installed correctly. The key to this is proper installation – properly dimensioned electrical system, well-made hydraulics, clean water in the system, and professional first start-up. Any shortcut during installation usually returns as a service intervention or a claim during the warranty period.

If you are choosing a specific model, see the topic How to choose an Attack Electric boiler: power, model and accessories or Attack Electric Excellent vs. Easy: what they differ in and which one to choose?. For selecting the right power for your home, see the article What power of electric boiler do I need for my home?

Do you have a question about this topic?

Not sure or dealing with a specific situation in your household? Write to us – we are happy to help.