Frequently Asked Questions about ELÍZ Electric Boilers
Frequently Asked Questions about ELÍZ Electric Boilers – Comprehensive Answers for Buyers and Users
ELÍZ electric boilers are among the most frequently searched electric heating units on the Slovak market. Their popularity is growing along with the interest in alternatives to gas heating, but so is the number of questions customers ask before purchase, during installation, and during regular operation. In this article, we gather the most pressing of them – with answers such as you would get from a technician who has seen these boilers installed in dozens of homes.
If you are looking for information about a specific model, we recommend checking out ELÍZ EQH 802, which is among the best-selling electric boilers in this category in Slovakia. In the following text, we will refer to it as a specific example where relevant.
How does the ELÍZ electric boiler actually work and how does it differ from a water heater?
This is the first question we get very often – and it's understandable, because the terms "electric boiler" and "electric water heater" tend to get mixed up in everyday speech. The ELÍZ electric boiler is used to heat water in a closed heating circuit, i.e., for heating. It heats water that circulates in radiators or underfloor heating and, after releasing its heat, returns to be reheated. It is not a hot water tank for washing or showering.
A water heater (storage heater), on the other hand, heats domestic water – the kind that flows from the tap. It works on a similar principle (also an electric resistive element), but it is a completely different circuit with different pressure conditions and hygiene requirements. The ELÍZ electric boiler can, of course, be supplemented with a domestic hot water tank, but on its own it does not perform this function.
The ELÍZ boiler itself works on the principle of resistive (or, in some models, PTC) electric heating. Electric energy is converted directly into heat with an efficiency close to 100% – which is why manufacturers can state an efficiency of 99.5% or more. There are no chimney losses, no combustion processes, and no emissions directly in the building.
What types of buildings and heating systems is the ELÍZ boiler suitable for?
ELÍZ electric boilers are essentially compatible with any water-based heating system – low-temperature radiators, panel radiators, towel radiators, underfloor heating, and fan coils. What matters is not the type of distribution, but the parameters: what temperatures the system requires and the total heating output the house needs.
In terms of buildings, the rule is: the better insulated the building, the more advantageous electric heating becomes. In new buildings constructed according to current thermal insulation standards, the ELÍZ electric boiler can cover the entire heating consumption at reasonable cost. In older buildings with poorer insulation, costs are higher, but it is technically functional – it just depends on the economic assessment of the specific case.
A practical example: a family house from 1985, 120 m², subsequently insulated (façade + roof), with replaced windows. Heat loss after insulation is about 6 kW. Such a house needs a boiler with an output of 6–8 kW, for example the ELÍZ EQH 802 in the appropriate power version. For more on how to correctly estimate the required output, see the article What ELÍZ Electric Boiler Output Do I Need for My House.
What are the electrical installation requirements? Is a standard household network sufficient?
This is one of the most practical questions, and also an area where customers most often receive inaccurate information. The answer depends primarily on the output of the selected boiler.
Boilers with an output of up to 3.5 kW can be connected to a single-phase 230 V network – a standard household outlet or a direct line. Boilers with an output of 4 kW and above require a three-phase 400 V network (3×400 V / 50 Hz). With a three-phase connection, the current load is distributed evenly and there is no risk of overloading a single phase.
Specifically: the ELÍZ EQH 802 in the 8 kW version requires a three-phase power supply. The circuit breaker must be sized according to the actual current draw – for an 8 kW three-phase unit, this is approximately 3×12 A at full output, so the breaker must be at least a 16 A three-phase type. It always applies that the electrical installation must be verified and approved by a qualified electrician, not merely visually inspected.
Another common question: does the entire electrical installation need to be replaced? Not necessarily. If the house already has a three-phase connection (which most family houses do), it is enough to run a supply line directly from the distribution board to the boiler room with the appropriate protection. Details can be found in the article Installing an ELÍZ Electric Boiler: Procedure and Installation Requirements.
How much does it cost to operate an ELÍZ electric boiler compared to gas?
There is no single universal answer to this question – it depends on energy prices at the given time, the appliance's output, how many hours the boiler actually runs, and the favorability of the tariff. Nevertheless, we can provide a specific framework.
In 2024/2025, electricity prices for households in Slovakia range around €0.15–0.22/kWh (depending on the supplier and tariff). With a low tariff (LT) for electric heating, the price can be lower – around €0.09–0.13/kWh, if you meet the distributor's conditions. Natural gas ranges around €0.07–0.10/kWh depending on the supplier and contract, and the efficiency of the gas boiler must also be taken into account (in practice 88–95% for a condensing boiler).
A rough calculation: a house with an annual heat consumption of 15,000 kWh would pay about €1,650/year with electricity on the low tariff (€0.11/kWh). With gas (€0.08/kWh, condensing boiler at 94%), it would be about €1,276/year. The difference is real, but smaller than many people think – and with further gas price increases or the use of photovoltaics, it could turn around. The topic of combining with photovoltaics is covered in more detail in the article ELÍZ Electric Boiler and Photovoltaics: Is the Combination Worth It.
What electricity clearly wins on: zero boiler servicing costs (gas boilers require a mandatory annual inspection costing €50–120/year), zero chimney and chimney-cleaning costs, and simpler installation. Over 10 years of operation, these servicing savings add up to €500–1,200.
Can I install the ELÍZ electric boiler myself, or do I need a professional?
This question has two parts: hydraulic installation and electrical connection. The hydraulic part – connecting to the heating system, installing the safety valve, expansion tank, and venting – is technically less regulated, and an experienced DIY customer can handle it. The ELÍZ boiler has standard threaded connections, and installation is basically similar to that of any other boiler.
The electrical connection is a different matter. Act No. 251/2012 Coll. and the relevant STN EN standards require that electrical equipment with an output above 3.68 kW at 230 V, or three-phase appliances, be installed by a qualified electrician. This means: the boiler must be connected by a person with the appropriate qualification, and the connection must be documented. Without this, your insurance company may refuse to cover damage from a potential electrical fault.
In practical terms: the vast majority of customers handled the hydraulics themselves or with the help of a heating technician, and entrusted the electrical connection to an electrician. It's a reasonable compromise – you save on heating technicians without taking on legal or safety risks with the electrical installation.
What is an expansion tank and safety valve – do I need to have them?
Yes, they must be there – and this is one of those things where it really doesn't pay to skimp or improvise. When water in a closed system heats up, its volume increases. The expansion tank "absorbs" this increase in volume – it is a closed vessel with a membrane, with pressurized air on one side and system water on the other. Without it, the pressure in the system would rise uncontrollably with every heating cycle.
The safety valve is a backup for cases where the expansion tank is insufficient or fails. It opens when the set pressure is exceeded (typically 3 bar) and releases some water, reducing the pressure. Without it, a malfunction could damage the boiler, cause pipes to burst, or – in an extreme case – cause the closed vessel to explode.
The size of the expansion tank depends on the volume of water in the system. As a rough guide: for every 100 liters of water in the system, you need about 12–15 liters of expansion tank capacity at a normal operating pressure of 1.5–2 bar. The correct calculation is done by the installer based on the specific parameters of the system.
What control options do ELÍZ boilers offer?
Modern ELÍZ boilers feature integrated control with a digital display, where you set the desired water temperature and a time program. The basic model works with four-stage or continuously variable output modulation – the boiler doesn't run at full output all the time, but reduces it as needed. This has a direct impact on energy consumption and thus on operating costs.
Some models in the ELÍZ range support connection to an external room thermostat – either wired or wireless. This means the boiler responds not to the water temperature, but to the air temperature in a reference room. The result is more precise and economical heating.
More advanced functions, such as weather-compensated control (the boiler adjusts the water temperature according to the outdoor air temperature), are available in more premium configurations. Weather compensation extends the time the boiler operates at lower output, which is more energy-efficient, especially with underfloor heating with high thermal inertia. A detailed guide on setting up the controls can be found in the article Setting Up and Programming the Controls of the ELÍZ Electric Boiler.
Is the ELÍZ electric boiler suitable for an apartment, or only for a family house?
ELÍZ electric boilers are also suitable for apartments – in certain situations, they are even an ideal solution. A typical scenario: an apartment disconnected from district heating (DH), or an apartment where the owner has opted for individual heating instead of expensive central heating. An electric boiler doesn't need a chimney or a gas connection, and it is quiet and compact.
Technically speaking, the boiler can stand directly in the kitchen or bathroom, provided there is sufficient space for access and operation (a minimum clearance of 600 mm in front of the boiler). Neither the law nor standards prevent the installation of an electric boiler in a living space, unlike gas boilers, where ventilation and flue gas path requirements are stricter.
The apartment area that an ELÍZ electric boiler can cover depends on its output. For an apartment of 60–80 m² with standard insulation, a boiler with an output of 4–6 kW is sufficient. For an apartment of 100–120 m² in an older building with poorer insulation, this may be 8–10 kW.
How long does it take to heat up the heating system after a cold start?
This depends on several variables: the volume of water in the system, the boiler's output, and the required temperature difference. A rough calculation: the energy needed to heat 1 liter of water by 1°C is 1.16 Wh. A typical family house heating system may contain 80–150 liters of water.
Example: a system with 100 liters of water, an 8 kW boiler, heating from 20°C to 70°C (outlet temperature). Energy required: 100 × 50 × 1.16 = 5,800 Wh = 5.8 kWh. At an output of 8 kW, this would take about 43 minutes to heat the water alone. In practice, heat released into the building during heating adds to this, so the actual time to reach operating temperature is 1–2 hours with a cold system.
This is why it's important to set the time program correctly – the boiler should start heating before you actually need the heat. Underfloor heating has even greater thermal inertia and needs an even longer warm-up time.
Can I connect the ELÍZ boiler to a domestic hot water (DHW) tank?
Some ELÍZ boiler models have a built-in outlet for preparing domestic hot water via an external tank (an indirectly heated tank with a heat exchanger). In that case, the boiler can serve both circuits – heating and DHW preparation – switching between them according to the set priority.
If your ELÍZ boiler model doesn't have this outlet, you don't lose anything – you simply add a separate electric DHW tank with its own power input. This is a technically cleaner solution and quite common in practice. The advantage of the combined approach via the boiler is a single control for both circuits, while the disadvantage is that heating slows down during DHW preparation.
What to do when the ELÍZ boiler shows an error or stops heating?
ELÍZ electric boilers have an integrated system of protections and diagnostics – in case of problems, they display error codes on the screen. The most common faults that customers resolve themselves:
- Low system pressure – the boiler reports low pressure and shuts off. Solution: top up water in the system via the filling valve, and set the pressure to 1.5–2 bar when cold. This is by far the most common reason why a boiler "doesn't work".
- Circulation pump fault – the pump gets stuck after standing idle for a long time (typically at the start of the season). Solution: manually release the pump shaft by unscrewing the cover on the front of the pump.
- Safety thermostat – overheating – the boiler has shut down via the safety thermostat due to overheating. Cause: air in the system, clogged filters, a closed valve on a radiator. The system needs to be vented and the flow checked.
- Electric element (heating element) fault – the resistive element has short-circuited or burned out. This already requires a service intervention and replacement of the element.
Detailed procedures for individual error codes and their solutions can be found in the article Common Faults of the ELÍZ Electric Boiler and Their Solutions. If you are unsure, don't delay a service intervention – faulty electrical equipment must be checked before it is put back into operation.
What about the safety of the ELÍZ electric boiler – could my house burn down?
ELÍZ electric boilers (like other certified electric boilers) are equipped with a multi-layered system of safety protective elements. These include: a safety thermostat with manual reset, a safety valve, minimum flow monitoring, dry-run protection (running without water), and electronic fuses in the electrical section.
With a properly installed boiler and a functional electrical installation, the risk of fire is extremely low – much lower than with gas boilers with improper sealing, or with failure to comply with inspection requirements. CE certification, compliance with the LVD (Low Voltage) directive, and the EMC directive are standard for boilers sold in the EU.
Practical advice: if you install the boiler in an enclosed technical room, consider installing a simple temperature or smoke detector. Not because the ELÍZ boiler is unreliable, but because every technical room deserves monitoring – even if it only contains a circuit breaker and a distribution board.
Is it worth switching from gas to an ELÍZ electric boiler?
The answer depends on your specific context, but there are several situations where it is clearly advisable: when you're planning to install photovoltaics, when you have an old or faulty gas appliance that's due for replacement, when you want to eliminate dependence on gas and the risk of price spikes, or when you're building a new house with good thermal insulation parameters.
On the other hand, if you have a relatively new condensing gas system and a house that requires a high heating output (a poorly insulated building over 200 m²), switching to electricity may not be economically advantageous without other measures (insulation, photovoltaics, a heat pump as a supplement).
An overview of what to consider and arrange before making the switch can be found in the article Switching from Gas Heating to an ELÍZ Electric Boiler: What You Need to Know. We also recommend a comparison with other electric boilers offered in the article ELÍZ Electric Boiler vs. Other Electric Boilers: Parameter Comparison.
What is the warranty period and service network for ELÍZ boilers?
The standard warranty period for ELÍZ boilers is 24 months for consumers (by law), while the manufacturer/importer may also provide an extended warranty if certain conditions are met (e.g., product registration, first installation by an authorized service provider). For the ELÍZ EQH 802, we recommend verifying the specific warranty conditions directly at the time of purchase.
As for the service network: electric boilers have the advantage that most experienced electricians and heating technicians can repair them – unlike more specific components of gas boilers, which require the manufacturer's authorized service. The resistive element, circulation pump, and expansion membrane are standardized components available at most hydraulic wholesalers.
Do I need to have the ELÍZ electric boiler inspected every year?
The legal obligation for regular inspections (as is the case with gas appliances) does not apply to electric boilers in the same way. The electrical installation as a whole is subject to inspections according to STN 33 1500 – periodic inspections for residential premises are every 7 years, and every 5 years for apartment buildings. The boiler itself is not subject to a separate annual inspection.
This doesn't mean the boiler doesn't need attention. An annual visual inspection (system pressure, venting, filter cleanliness, functionality of the safety valve and circulation pump) is good practice that can prevent bigger problems. Read more in the article Maintenance and Servicing of the ELÍZ Electric Boiler: How to Extend Its Lifespan.
Frequently Asked Questions (FAQ)
Can the ELÍZ electric boiler also be used to prepare hot water for showering?
The boiler itself is not designed to prepare domestic hot water (DHW) – it is used exclusively for heating water in the heating circuit. A separate storage water heater (boiler) or a DHW tank connected to the boiler via a heat exchanger is used for preparing water for washing and showering. Some ELÍZ models have an inlet for an indirectly heated tank, where the boiler can also supply the DHW circuit by heating the tank.
What does "output modulation" mean for an ELÍZ boiler, and why is it important?
Output modulation means that the boiler doesn't operate only in a binary on/off mode at full output, but can reduce output in stages or continuously. For example, an 8 kW boiler can operate at 2 kW, 4 kW, 6 kW, or 8 kW depending on current needs. This is more energy-efficient – the boiler runs longer at a lower output instead of short full-power cycles, which minimizes heat losses and component wear.
Can I connect the ELÍZ electric boiler to solar thermal collectors?
Not directly – an electric boiler and solar collectors are two separate heat source devices. In practice, they are commonly combined via a bivalent tank or hydraulic fitting, where the solar collectors have priority and the electric boiler only kicks in when solar gain is insufficient. This is a fully functional and energy-efficient solution, but the hydraulic scheme is more complex – it requires an experienced design installer.
Is it normal for the boiler to make sounds while heating up?
Slight cracking or ticking sounds during heating are a normal physical phenomenon – thermal expansion of the pipes and boiler tank. If the sounds are intense, bubbling, or rumbling, this may indicate air in the system (solution: vent all radiators and air vents), or deposits on the resistive element (solution: flush the system or use a chemical cleaning agent). Loud, distinct knocking may indicate incorrect pressure in the expansion tank.
What is the difference between the ELÍZ EQH and other ELÍZ boiler ranges?
The EQH series represents the standard commercial line of ELÍZ boilers with digital control, multi-stage output, and the option to connect an external thermostat. The ELÍZ EQH 802 model is specifically the 8 kW version of this series. Various numerical designations generally refer to the power version (802 = 8 kW, variant 2) and specific equipment – we always recommend reviewing the technical data sheet of the specific model or consulting with a seller, as designations may vary by model year.
What is the lifespan of an ELÍZ electric boiler and what affects it?
With proper installation and regular (even if simple) maintenance, an ELÍZ electric boiler can be expected to have a lifespan of 15–20 years. Key factors affecting lifespan: water quality in the system (hard water accelerates limescale buildup on the resistive element), the presence of air in the system (internal corrosion), correct pre-pressure of the expansion tank (pressure fluctuations put strain on fittings), and whether the boiler operates in continuous modulation or in extreme start-stop cycles.
Conclusion: The ELÍZ Electric Boiler as a Reliable Choice with the Right Selection and Installation
ELÍZ electric boilers are not miracle devices that solve every heating problem – but in the right context, they are reliable, low-maintenance, and economically sensible. The key is choosing the right output (neither oversized nor undersized), responsible installation (a quality heating technician + electrician), and understanding how the device works.
If you're considering a purchase, start by selecting the right model – the article How to Choose an ELÍZ Electric Boiler: What to Focus on Before Buying will help you with that. If you've already bought a boiler and are dealing with installation, go through the article Installing an ELÍZ Electric Boiler: Procedure and Installation Requirements in detail. And if you're thinking about switching from gas or combining with photovoltaics, other topics in the Knowledge Center will give you a further basis for making an informed decision.
The entire range of ELÍZ electric boilers, including current models and prices, can be found in the ELÍZ category on atria.sk.
Do you have a question on this topic?
Can't decide, or are you dealing with a specific situation in your household? Write to us – we're happy to help.