Installation of ORAVA electric boiler – procedure, requirements and what the electrician must do

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Installation of the electric boiler ORAVA – complete guide to the process, requirements and electrician work

An electric boiler is one of the simplest types of heating technology. It has no combustion chamber, does not require a chimney, does not require gas distribution or a soil survey before the installation of a heat pump. Despite this, the installation of an electric boiler – and specifically boilers of the ORAVA range – is not a task that a layperson can handle on their own over the weekend. The reason is simple: the electrical side of the installation is subject to strict standards, affects the power electrical installation of the building and in case of incorrect wiring can endanger lives and property. Therefore, the purpose of this article is to give you a complete picture of the entire process – from planning through hydraulics to the final handover of the work by the electrician.

If you are still deciding between a boiler and a convector, first see the article Electric boiler vs. convector ORAVA – which type of heating is more cost-effective. If you are solving the power sizing, I recommend the article What power of ORAVA electric boiler do I need for my household. Here we assume that you have decided on a boiler and you are going to solve the specific installation.

Why the ORAVA electric boiler and what to pay attention to right from the start

Boilers of the ORAVA range are designed for central heating – this means that they heat water in a closed circuit and distribute it through a system of pipes and radiators (or floor loops). They are full-fledged replacements for gas or oil boilers, with their main advantage being minimal service requirements and zero need for a chimney.

The specific models you will find in the range differ mainly in power and design:

ORAVA EK-2003 – a compact electric boiler suitable for smaller apartments or studios, or as supplementary heating
ORAVA EK-2004 – a more powerful variant for medium-sized houses, offers a higher level of regulation
ORAVA VL-202 – a boiler with an integrated tank, suitable also for heating hot utility water
ORAVA VL-201 – a basic model of the tank design for smaller installations

Before you call an installer or electrician, you must know the answers to three basic questions: What power boiler are you planning to install? Do you have a single-phase or three-phase connection? And what is the capacity of your main circuit breaker box? Answers to these questions determine the entire further process.

Prerequisites before installation – what you need to have resolved

Electrical connection and protection

Electric boilers are power consumers. Even a smaller model with a power of 4 kW on a single-phase network (230 V) draws a current of around 17.4 A. Medium power boilers with a power of 9–12 kW already require three-phase power supply 3×400 V and a circuit breaker of at least 16–25 A per phase. More powerful boilers, for example 18 kW and more, require protection of 25–32 A per phase and cable cross-sections of 6 mm² (copper) or even 10 mm².

In practice, this means: if you have an old family house with an old circuit breaker panel, you will very likely have to solve the modification of the electrical installation before the actual installation of the boiler. This is also the most common "hidden cost" that customers do not think about before buying a boiler. The electrician must check:

Capacity of the HDO (main household metering point) and the main circuit breaker
Condition and capacity of the distribution board in the house
Cable cross-section of the existing cable from the distribution board to the boiler installation location
Presence of a protective conductor (PE) along the entire route
Condition of the grounding of the entire building

If the house does not have a three-phase connection, but you need a boiler over 3.5 kW, you must first ask the electricity distributor to change the connection. This process usually takes 4–8 weeks and costs from several hundred to a thousand euros – depending on the distance to the substation and the condition of the public network.

Hydraulic system – condition of the existing distribution

If you are replacing an old boiler (gas, oil), the entire hydraulic system must be checked. An electric boiler has a lower maximum temperature of the output water compared to conventional boilers (most ORAVA models operate up to 85 °C, normal operation at 55–70 °C). Therefore, older radiator systems designed for 90 °C may provide lower heating power when switching to an electric boiler – and you will have to either add radiators or increase the boiler power.

In a new installation, the situation is simpler, but the entire distribution must be designed. For floor heating, an electric boiler is also suitable, but the floor loop operates at lower temperatures (35–45 °C), which is an advantage – the boiler does not have to operate at full power and its lifespan is extended.

Step by step: installation of electric boiler ORAVA

Step 1 – Choosing the installation location

The electric boiler ORAVA can be installed almost anywhere in the interior – boiler room, technical room, hallway, or even in a larger utility room. Since no combustion byproducts are produced, no chimney or special room ventilation is required (unlike with a gas boiler). Despite this, we recommend a technical room for practical reasons: easier access for service, resistance to humidity and frost, and space for an expansion tank and other hydraulic components.

When choosing the location, pay attention to:

Minimum distance from flammable materials according to the manufacturer's instructions (usually 50–100 mm on the sides, 200 mm on top)
Availability of a condensate drain or safety valve – this must have a place to discharge water in case of pressure overloading
Sufficient space for maintenance and possible replacement of the heating element (at least 600 mm in front of the boiler)
Closeness to the electrical connection – the shorter the cable route, the lower the losses and costs
Wall load capacity in the suspended version – the boiler with water can weigh 30–60 kg

Step 2 – Preparation of the hydraulic connection

The plumber (heater installer) handles the hydraulic part. The boiler is connected to a closed heating circuit. Typical components that must be part of the installation:

Expansion tank – compensates for thermal expansion of water. For a typical family house with a water content in the system of 100–150 liters, you need an expansion tank of at least 18–25 liters. Many ORAVA models have an integrated expansion tank – it is necessary to check the technical sheet of the specific model.
Circulation pump – ensures water circulation in the circuit. Again, some boilers have it built-in. If not, it must be installed externally.
Pressure relief valve – typically set to 2.5–3 bar. It is a mandatory part of every closed system. No closing element must be behind it.
Pressure gauge – for visual pressure control in the system.
Ball valves – on the supply and return pipe, so that the boiler can be isolated without draining the entire system.
Filter (magnetic separator) – captures impurities and sludge from the system, which could damage the heating element. For old systems, this is critically important.
Automatic air vent – at the highest point of the system.

After the hydraulic connection is made, the system is filled with water (ideally treated or demineralized, or with corrosion inhibitor) and pressurized to an operating pressure of 1.0–1.5 bar when cold. The pressure test is carried out before connecting the electricity and before the first start-up.

Step 3 – Electrical connection (work of the electrician)

This is a key phase that must be carried out by an authorized person – an electrician with a valid certificate according to Decree No. 508/2009 Coll. (Decree on the safety of electrical equipment). DIY installation of power wiring is not only dangerous, but also illegal and causes the invalidation of property insurance.

What the electrician specifically deals with during the installation of the ORAVA boiler:

Cable sizing and selection – for a three-phase boiler of 9 kW, a 5G 2.5 mm² (Cu) cable is used, for 12–18 kW a 5G 4 mm² cable, for powers of 18+ kW a 5G 6 mm² cable. Aluminum conductors are unsuitable for boilers.
Installation of protective devices in the distribution board – each boiler must have its own circuit breaker and residual current device (RCD) with sensitivity 30 mA. The RCD is legally required for tenants in apartment buildings and recommended for single-family homes. The circuit breaker is dimensioned according to the boiler's power.
Physical cable laying – the cable must be routed in a protective conduit (tray or pipe), protected against mechanical damage, thermal stress and moisture. In walls, it is laid in grooves with a minimum 5 cm plaster cover.
Connection to the boiler terminal block – the terminal block is usually accessible after opening the boiler cover. Individual conductors (L1, L2, L3, N, PE) are connected to the correct terminals exactly according to the connection diagram in the installation manual. Each manufacturer has an exact diagram – NEVER improvise.
Earthing – the protective conductor PE must be reliably connected to the boiler's earthing terminal. The boiler must be integrated into the building's earthing system (TN-S or TN-C-S).
Connection of thermostat or control unit – most ORAVA boilers allow connection of an external room thermostat. The thermostat is connected to low-voltage terminals (not power ones) – typically 230 V AC or a potential-free contact. There is also space for connecting HDO (remote control) for night tariff.

Step 4 – First start-up and boiler setting

After completing the electrical connection and a successful hydraulic pressure test, the first start-up can take place. Ideally, this should be carried out by a technician or at least an experienced installer together with an electrician.

During the first start-up, the following is checked:

Proper air bleeding from the system – the system is allowed to heat up and air is gradually bled from the radiators from the furthest to the nearest to the pump
Functionality of the circulation pump – we listen for the typical quiet sound of operation, no knocking or vibrations
Tightness of all connections – checked after 10–15 minutes of heating
Temperature of the supply and return pipe – in normal operation, the difference is 10–15 °C, indicating correct flow rate
Functionality of the thermostat and regulation – the boiler must correctly respond to the thermostat's request (turn on, turn off)
Correct power setting – most ORAVA boilers allow setting the maximum power (full power, 2/3 power, 1/3 power), which is important for seasonal regulation
Recording in the inspection log – the electrician issues a report on the professional inspection and test

What the electrician must do – a detailed view

Many customers underestimate the scope of work performed by an electrician during boiler installation. An electrician is not just someone who "connects cables" – their responsibility is much broader, and there are specific legal obligations when performing their work.

Technical inspection and test (OPS)

After completing each new installation or a significant change to the electrical installation, the electrician is required to prepare a technical inspection and test report (OPS) according to the standards STN 33 1500 and STN EN 60364. This report includes:

Visual inspection – correctness of the wiring, mechanical protection, conductor labeling
Insulation measurement – the minimum insulation resistance of conductors is 0.5 MΩ for power electrical installations
Grounding measurement – the resistance of the grounding system must not exceed specified values
Verification of the residual current device (RCD) – the RCD is tested using a test button and a measuring device
Verification of circuit breaker selectivity – checking that only the boiler's circuit breaker trips in the event of a fault, not the entire house distribution board

Without this report, the installation is not legal, and in the case of a fire or accident, you may have problems with the insurance company. The OPS report is a document that you should keep together with the boiler manual and the installation invoice.

Circuit breaker sizing – specific values

For orientation, here are typical circuit breaker values for different boiler powers:

Boiler power	Power supply	Minimum cable cross-section (Cu)	Circuit breaker	Residual current device
up to 3.5 kW	1× 230 V	3G 2.5 mm²	B16 A (1-pole)	30 mA, 25 A
4 – 6 kW	3× 400 V	5G 2.5 mm²	B10 A (3-pole)	30 mA, 25 A
7 – 12 kW	3× 400 V	5G 4 mm²	B20 A (3-pole)	30 mA, 40 A
13 – 18 kW	3× 400 V	5G 6 mm²	B25 A (3-pole)	30 mA, 40 A
18 – 24 kW	3× 400 V	5G 10 mm²	B32 A (3-pole)	30 mA, 63 A

These values are approximate and apply for a maximum cable length of approximately 20–30 m. For longer runs, the electrician must calculate voltage drop and possibly choose a larger cross-section.

Remote control – HDO and two-rate tariff

Electric boilers can be operated under a two-rate tariff (D45d or D56d with SSE/ZSE/VSE), where the distributor provides cheaper energy during night and off-peak hours. The condition is the installation of an HDO receiver, which signals the boiler to allow heating. The electrician must connect the boiler's HDO input to the output contacts of the HDO receiver. This input is usually potential-free (dry contacts) and must not be confused with the power supply.

From a cost-saving perspective, this is very important – with the D45d tariff, you can have cheap energy for 20–22 hours a day, which for an annual boiler consumption of 10,000 kWh can mean a difference of hundreds of euros. More on optimizing heating costs can be found in the article Electric heating ORAVA and energy consumption – how to reduce heating costs.

Common installation errors with electric boilers

From practice we know that most problems with electric boilers do not stem from a fault in the boiler itself, but from installation errors. Here are the most common ones:

Undersized electrical connection

The customer buys a 12 kW boiler, but the electrician discovers upon arrival that the house has a single-phase connection of 16 A, which can handle a maximum of 3.5 kW. Solution: coordination of the boiler's power with the capacity of the connection before purchase. More on this can be found in the article What power of ORAVA electric boiler do I need for my household?.

Missing filter/magnetic separator

In older systems (steel radiators, cast iron bodies), corrosion and sludge accumulate over the years. Without a filter before the boiler, this sludge gets directly onto the heating element, where it settles, reduces heat exchange and shortens the life of the element to a fraction of the normal period. Filter installation costs 20–50 euros and saves thousands.

Wrong expansion tank

It is either missing or undersized. When heating water from 10 °C to 80 °C, the volume of water in the system increases by about 3–4 %. For a system with 200 liters, this means 6–8 liters of excess water that must be absorbed by the expansion tank. If the tank is too small or its membrane is damaged, the safety valve opens, water is lost and the system must be refilled.

Boiler without inspection

The customer asks a neighbor electrician to connect the boiler "in the dark" without preparing an electrical inspection report. For several months everything works fine. Then a failure or fire occurs for a completely unrelated reason. When the insurance company investigates, it finds that the electrical installation has no inspection and refuses to pay the claim. This scenario is not hypothetical – it is common.

Direct contact with water in suspended installation

A leaky connection above the boiler dripping directly onto the electrical terminal block or power cable. Water and electricity is a dangerous combination. All hydraulic connections above the boiler must be as reliably sealed as possible and checked after installation.

ORAVA VL-201 and VL-202 storage boilers – installation specifics

Models ORAVA VL-201 and ORAVA VL-202 combine the function of a heating boiler with a hot water storage tank (DHW). For their installation, all the above rules apply plus a few additional specifics:

Cold water pressure – the storage heating is connected to the water supply. The pressure of the cold water must be in the range of 0.3–6 bar (depending on the specific model). If the pressure in the water supply network is higher, it is necessary to install a pressure reducing valve.
Pressure relief valve on the DHW side – separately from the pressure relief valve of the heating circuit! Each circuit has its own pressure relief valve.
Descaling of the tank – the DHW tank must be descaled at least once a year – to drain the sediments from the bottom. For this, a drain cock must be designed at the bottom of the tank.
Legionella protection – with DHW tanks, there is a risk (with long-term standing water at 40–55 °C) of multiplying the Legionella bacteria. The boiler must be set so that it heats the water in the tank to at least 65 °C at least once a week (legionella program). Most ORAVA boilers have this setting automatically.

Requirements for warranty and service

The manufacturer and seller provide warranties provided that the installation is carried out correctly and in accordance with the instructions. Specifically, this means:

Installation must be carried out by a qualified person (an electrician with a valid certificate for the relevant group)
There must be an electrical inspection report (or a commissioning record from the installation technician)
The boiler must be operated within the permitted technical parameters (pressure, temperature, power)
Regular maintenance must be ensured according to the instructions – more on this in the article Maintenance and service of ORAVA electric boiler – what and how often to check

In the case of a complaint, the manufacturer (or authorized service) checks for traces of incorrect installation – traces of corrosion caused by unsuitable water, mechanical damage, burned-out terminals (a sign of insufficient protection or poor contact), and so on. It is not bureaucracy for bureaucracy – it is real protection of the investment.

Installation costs – what you really pay

Customers regularly ask us how much installation costs. The answer depends on many factors, but roughly for a typical family house (replacing an old boiler with a new electric one, without major modifications to the electrical installation):

Electrician's work – cable laying (up to 15 m, no drilling), installation of protective devices, connection, inspection: 150–350 euros
Electrical materials – cable 5G 4 mm² (approx. 20 m), circuit breaker, differential switch, rail, cover: 80–200 euros
Plumber's work – hydraulic connection of the boiler, valves, expansion tank, pump (if missing): 200–500 euros
Hydraulic materials – depends on the condition of the existing system: 100–400 euros
Modification of the distribution board / connection – if needed: 300–1500 euros (large variation)

Overall, therefore, under favorable conditions (good existing system, nearby distribution board), installation will cost 500–800 euros for labor and materials without the boiler. In more complicated situations (old electrical installation, need for long cable laying, replacement of the distribution board), you can plan for 1500–3000 euros for infrastructure preparation.

Frequently asked questions (FAQ)

Can I connect an ORAVA electric boiler myself if I have "DIY" experience with electricity?

No. Connecting a high-power consumer to the grid (and this applies to every boiler with a power of more than 3.5 kW) requires a person with a valid professional certificate according to Decree No. 508/2009 Coll. Without a certificate, the installation is illegal, the boiler has no valid inspection and the warranty conditions are automatically violated. In addition, connecting a three-phase boiler with incorrect phase sequence or without a PE conductor can cause fatal injury or fire.

How long does the entire installation take from preparation to start-up?

Under favorable conditions (existing sufficient connection, system in good condition), an experienced team of electrician + plumber can complete the entire installation in 1–2 working days. If the electrical connection needs to be modified with the distributor, the entire process is extended by 4–8 weeks of waiting for administration. Therefore, it is always better to start planning the installation 2–3 months before the heating season.

Is a building permit required for the installation of an electric boiler?

Usually not – when replacing an existing boiler with an electric one without changing the load-bearing structures, a building permit is not necessary. An exception may be the situation where the boiler is part of a larger reconstruction or if it is a property under heritage protection. In any case, a change in the heating system must be reported to the building authority as a notified minor construction in some municipalities – check this at the local office.

Can I operate an electric boiler in summer only for hot water heating?

Yes, but only with models with a DHW tank, i.e. ORAVA VL-202 or ORAVA VL-201. Boilers without a tank (e.g. ORAVA EK-2003 or EK-2004) are used exclusively for heating and do not have a DHW circuit. For summer DHW preparation, you would need a separate heater or tank.

What pressure should the system have after filling and how much water is filled into it?

The cold system (before heating) is filled to a pressure of 1.0–1.5 bar. During operation at temperatures of 60–75 °C, the pressure increases by 0.3–0.6 bar, i.e. to 1.3–2.1 bar. The safety valve typically opens at 2.5–3 bar – this is a safety margin. Too low pressure (below 0.8 bar) causes an error message and boiler shutdown. Too high pressure (continuous opening of the safety valve) indicates a problem with the expansion tank.

Can one electrical connection power the boiler and other appliances in the house?

Yes, but with limitations. The boiler must have its own circuit breaker and ideally its own residual current device (RCD) – this is a requirement of the electrical safety regulations. The current drawn by the boiler (e.g. 12 kW = 17.3 A per phase) is added to that of other appliances, and the total load must not permanently exceed the capacity of the main circuit breaker. If you have a 25 A main circuit breaker and the boiler itself draws 17 A, only 8 A remains for other appliances on the same phase – whether this is acceptable or not in a three-phase load distribution depends on the specific appliance distribution in the house.

Conclusion – why proper installation is worth doing

The ORAVA electric boiler is a reliable and long-lasting appliance – provided it is installed correctly. Proper installation means an electric supply line of the correct dimension, appropriate circuit protection with an RCD, high-quality hydraulics with an expansion vessel, filter and safety valves, and the first start-up with professional supervision and inspection.

Do you have a question on this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.