Frequently Asked Questions about Viessmann Vitotron electric boilers

We are still preparing products.

But you can look at other categories.

Frequently Asked Questions about Viessmann Vitotron Electric Boilers – Answers from Experienced Technicians

Viessmann Vitotron electric boilers are among the best-selling electric boilers on the Slovak market and also among those about which customers have the most questions. Not because they are complicated – quite the opposite. But precisely because interest in them is growing quickly and many people come to them without prior experience with electric heating. This article collects dozens of questions that actually come up during sales, installation, and service visits, and answers them the way a technician who has seen hundreds of similar installations would.

If you're looking for an answer to a specific question, go to the relevant section. If you're still in the selection phase, we recommend reading the whole article – many answers are related to each other and understanding one helps understand the next.

What exactly is the Vitotron and how does it work?

The Viessmann Vitotron is an electric flow-through boiler – a device that heats water in the heating system using electricity. Unlike a gas boiler, it has no combustion chamber, flue, or gas supply. Water flows through an electric resistance heating element (electric coil or ceramic module), which heats it to the required temperature, and this hot water then circulates through radiators or underfloor heating.

The principle is very simple, which is also one of the main advantages of the Vitotron: fewer moving parts mean fewer possible failures. Compared to a gas boiler, there is no need for gas pipe inspections, burner cleaning, replacing ionization electrodes, and so on. The only active parts are the pump, the heating element, and the controller's electronics.

The Vitotron is available in several power output variants. For smaller apartments and houses, there's the Viessmann Vitotron 100 in the 0.4 – 8.0 kW range, while for larger buildings the Viessmann Vitotron 100 in the 1.0 – 24.0 kW range is intended. Both models work with continuously modulated output, which is an important feature – the boiler doesn't always run at full power, but regulates itself according to actual heat demand.

What output does my Vitotron need?

This is the most practical and also the most common question. The calculation is as follows: as a rough guide, you need 80–120 W per m² of heated space in a standard insulated house. In a well-insulated low-energy house, the requirement may be lower – 50–80 W/m².

A real-life example: A 75 m² apartment in a prefabricated building after window renovation and insulation. Calculation: 75 × 90 W = 6,750 W, i.e. around 7 kW. A Vitotron 100 in the 0.4–8.0 kW range would be sufficient. If it were an older, uninsulated house, you would need a margin and would reach for the Vitotron 100 with output up to 24 kW.

Important: The Vitotron regulates output continuously (e.g. the model up to 8 kW can run at 0.4; 1.0; 1.5; 2.0; 3.0; 4.5; 6.0 or 8.0 kW as needed), so you don't need to worry about the boiler being "too big" – excess capacity simply won't be used. Undersizing is much worse. You can find out more on this topic in the article What output Vitotron do I need for my house or apartment.

Is the Vitotron suitable as the sole heat source, or only as a supplementary one?

Both are possible – it depends on the specific situation. The Vitotron was designed primarily as a full-fledged main heat source for houses and apartments connected to an electrical grid with sufficient capacity. In practice, however, we encounter both scenarios:

Primary heat source – most often in new buildings, apartment units, and renovated properties where the owners wanted to remove the gas boiler or where gas isn't connected at all.
Backup/supplementary source – for example, with a heat pump as the main source and the Vitotron as a bivalent supplement for extremely cold days. Or in houses with a fireplace/stove as a supplement.
Interim solution – during renovations, where the old gas boiler has been temporarily decommissioned and a new device is awaited (the Vitotron handles this scenario without any problems).

One real-life customer example: A 120 m² house, originally with a gas boiler, whose owner switched to an air-to-water heat pump. He installed a Vitotron 100 up to 24 kW as a backup and to cover peaks. The heat pump handles 90% of the season on its own, and the Vitotron kicks in when temperatures drop below -10 °C, when the pump isn't enough. A perfect solution.

What electrical connection is needed for the Vitotron?

This is a technical question where customers most often make mistakes. The Vitotron 100 up to 8 kW can be connected to a single-phase 230 V network, but only certain versions – this must always be verified in the technical documentation of the specific model. Most higher-output versions, and certainly the Vitotron 100 up to 24 kW, require three-phase power supply 3 × 400 V / 50 Hz.

Practical advice for those still in the planning phase: Before ordering a boiler, check what electrical connection you have in your distribution board. If your house has only a single-phase supply, installing a powerful Vitotron will require intervention by the distribution company and an upgrade of the connection – this can take weeks and cost several hundred euros extra. It's better to find this out in advance.

Furthermore: For the Vitotron 24 kW at full output, the current flowing is around 35 A per phase. You need appropriately sized cabling (at least 6 mm² Cu) and a correctly rated circuit breaker. These matters are handled by an electrician, not the boiler installer – but if you arrive unprepared for installation, you can lose a day and the entire installation will be delayed.

What is HDO and how does it affect the operation of the Vitotron?

HDO (ripple control / remote load control) is a system by which the electricity distributor temporarily disconnects certain customers from the grid during peak load, or manages payments for the low tariff (off-peak). The Vitotron has an input for the HDO signal, which allows it to automatically adapt operation to tariff conditions.

In practice, it works like this: If you have a dual-tariff metering contract (peak/off-peak) with the distributor, the boiler can be set to preheat the DHW tank or store heat in the storage system during the off-peak period. During the peak tariff, only the most necessary outputs run. With proper settings, you can reduce operating costs by 15–30% compared to simple operation without a tariff.

Important: The HDO input of the Vitotron doesn't restrict the heating function itself in any way. If only the tank is set to HDO and heating isn't, the boiler will heat normally in both tariffs – only the DHW tank is preferentially charged during the off-peak period.

Can the Vitotron also heat domestic hot water (DHW)?

The standard Vitotron 100 without accessories only heats the water in the heating system (central heating). To heat DHW, you need either:

Vitotron with a 3-way diverter valve – these models have an integrated 3-way valve that can switch between the heating circuit and the DHW tank charging circuit. Available as the Vitotron 100 with 3-way valve up to 8 kW and the Vitotron 100 with 3-way valve up to 24 kW.
An external tank with its own electric heating element – the tank has its own electric heating coil, and the boiler only handles heating.
A tank connected via the boiler (indirect heating) – the boiler heats the water in the tank via a heat exchanger; the boiler must have sufficient output for both circuits.

The version with the 3-way valve is more elegant from an installation perspective – everything is in one compact unit, and the tank switches automatically according to priority (usually the DHW tank has higher priority, so you never run out of hot water). The tank sensor measures the water temperature in the tank, and the boiler knows exactly when the tank needs reheating. You can find more details on this topic in the article Vitotron with a 3-way valve and tank sensor – when it's worth it.

How much does it cost to run the Vitotron? Is it expensive?

This is a question that doesn't have a simple answer – it depends on many factors. Electricity is in principle more expensive than natural gas, but that's not the whole story. The comparison must take into account:

The price of electricity (current tariff, dual-tariff metering)
The heat losses of the house (insulation, windows, roof)
The method of regulation and boiler settings
Installation and service costs (significantly lower for an electric boiler than for gas)
The need for inspections (an electric boiler doesn't need an annual mandatory inspection like gas does)

An illustrative real-life example: A 60 m² apartment in a well-insulated prefabricated building. Heat consumption approx. 8,000 kWh/year. At an electricity price of €0.18/kWh (off-peak) and an average price of €0.22/kWh including the peak/off-peak mix: annual heating costs approx. €1,400–1,800. That's not a small amount, but the saved service costs (no mandatory burner inspection, no gas inspection, no electrode replacement) can be €150–300 per year. You can find more details on this topic in the article Vitotron operating costs – how much does it cost to heat with an electric boiler.

One thing is certain: the Vitotron has an efficiency of practically 100% – all the electrical energy is converted into heat, nothing "escapes" through a chimney. A gas condensing boiler has an efficiency of 96–98%, while other types of gas boilers have less. From a physical standpoint, the Vitotron is therefore a maximally efficient device.

What control options are there – can I control it via an app?

The Vitotron 100 has an integrated controller with a display, where you can set the water temperature, operating schedule (day/night setback), and DHW tank priority. Basic control is fully functional without any accessories.

For smarter control, there are extended options:

External room thermostat – the Vitotron can connect an external thermostat (potential-free contact), which controls the boiler based on the actual room temperature, not just the water temperature. This is the basis of comfortable control.
Vitotronic / Viessmann ViCare – Some Vitotron versions are compatible with the Viessmann ViCare ecosystem, which allows control via smartphone. The Vitotron 100 in its base version doesn't have this function natively, but it can be connected via a communication module.
Weather-compensated control – The Vitotron allows connection of an external temperature sensor and automatic weather-compensated control (the boiler adjusts the heating water temperature according to the outdoor temperature). This is a very efficient and recommended function, especially with underfloor heating.

Weather-compensated control is a function that many customers underestimate, but in practice it saves 10–20% of energy. With underfloor heating, it's even essential – underfloor heating has enormous thermal inertia and is difficult to regulate without weather compensation. With weather compensation, the boiler "anticipates" weather changes and adjusts output before it's felt indoors.

Must installation of the Vitotron be done by a certified technician?

Yes and no – it depends on what exactly you mean by installation.

Hydraulic installation (connection to the heating system) formally doesn't require special certificates, but we recommend entrusting it to an experienced plumber who understands hydraulic principles. Incorrect hydraulic connection is the most common cause of poor performance or noise in the system.

Electrical connection must be carried out by an electrician with the appropriate qualification in accordance with Slovak Act No. 124/2006 Coll. (Occupational Health and Safety Act) and relevant standards (STN 33 2000). A boiler with an input over 3.68 kW must be connected to a fixed installation (not a plug), by a certified electrician. This is not a recommendation – this is a legal requirement.

Warranty service and settings – Viessmann requires that the initial start-up and basic setup of the device be carried out by an authorized service technician, otherwise the warranty may be voided. This is standard practice among all premium boiler manufacturers. You can find a list of authorized service partners on the Viessmann Slovakia website.

You can find more about the installation procedure in the article Installing the Viessmann Vitotron electric boiler step by step.

What is the difference between the Vitotron 100 and the Viessmann EKCO.TM?

This question has come up many times. The Viessmann EKCO.TM 10-30 is an electric boiler with an output range of 10–30 kW, intended primarily for larger buildings, industrial, and commercial applications. The main differences compared to the Vitotron 100:

Output range: The EKCO.TM starts where the Vitotron 100 ends – from 10 kW. For family houses and apartments, the Vitotron is generally sufficient, while the EKCO.TM is for larger projects.
Construction: The EKCO.TM has a more robust design for more demanding operating conditions (schools, offices, smaller commercial premises).
Control: Both boilers have advanced controls, but the EKCO.TM is primarily designed for professional installations with BMS systems.
Price: The EKCO.TM is significantly more expensive – justified by its higher output and durability.

For a typical family home, choose the Vitotron 100. Consider the EKCO.TM only when you need an output above 24 kW or special integration into an industrial system.

Is it possible to connect the Vitotron to an underfloor heating system?

Yes, the Vitotron is fully compatible with underfloor heating. However, several important rules must be followed:

Water temperature: Underfloor heating usually operates at temperatures of 30–45 °C (a low-temperature system). The Vitotron can set the outlet temperature precisely to this range. This is much more efficient than heating with radiators (55–75 °C) in terms of losses, and it's also more comfortable for residents.

Weather-compensated control: For underfloor heating, weather-compensated control is practically essential. The reason: the floor has enormous thermal inertia (thickness of concrete, tiles). If the boiler only reacted to a drop in room temperature, the floor would heat up too late and then overheat. With weather compensation, the water temperature is adjusted in advance based on the outdoor temperature.

Manifold and thermostatic heads: The Vitotron can be supplemented in an underfloor system with a manifold with thermostatic actuators for each circuit separately. The boiler then continuously regulates output according to the number of open circuits – with a modulating Vitotron, this is an ideal combination.

Mixing valve: If you want to combine underfloor heating with radiators (different water temperatures), you need a mixing valve or a hydraulic manifold. This is a classic installation in family houses – underfloor heating on the ground floor (35 °C), radiators upstairs (55 °C). The Vitotron is capable of supplying such a system, but the hydraulics must be designed by an experienced designer.

What are the common causes of failures and how can they be prevented?

An electric boiler is inherently more reliable than a gas one, but problems can still occur. In practice, the most common scenarios are:

Limescale buildup on heating elements – hard water (higher CaCO₃ content) deposits limescale on the heating element. The result is lower efficiency, potential overheating, and reduced lifespan. Solution: a water softener or regular inspection and cleaning. This applies doubly for areas with hard water (part of the Záhorská lowland, northern Slovakia).
Impurities in the system (sludge, corrosion) – an old radiator system may contain sludge, rust, and impurities. When a new boiler is connected to an old system, these impurities can damage the pump and heating element. Solution: always flush and clean the entire system before installing a new boiler, ideally with a chemical flush, and install a magnetic filter on the return pipe.
Air in the system – air causes noise (gurgling, squeaking) and reduced performance. Solution: bleed the radiators and install automatic air vents on the manifold.
Expansion vessel malfunction – the expansion vessel must be properly pre-charged with nitrogen. An undersized or malfunctioning expansion vessel leads to pressure switch failures and repeated boiler errors. Check the pressure at least once a year.

You can find more about troubleshooting in the article Common faults of the Viessmann Vitotron and how to fix them. For prevention, see Maintenance and servicing of the Vitotron electric boiler – what and how often.

What are the dimensions of the Vitotron 100 and where can it be installed?

The Vitotron 100 is a fairly compact device. Approximate dimensions (depending on the specific output version):

Height: approx. 450–750 mm (depending on version and output)
Width: approx. 440–500 mm
Depth: approx. 200–270 mm
Weight: 12–25 kg depending on output

The boiler is wall-mounted. You need a bracket (supplied with the boiler) and a solid load-bearing wall (masonry or concrete – not plasterboard without anchoring to a load-bearing structure). The minimum distance from flammable materials and from the ceiling/side walls is specified in the installation manual and is usually 50–100 mm. For service access, we recommend keeping at least 600 mm of free space in front of the boiler.

Compared to a gas boiler, the Vitotron has one major advantage in terms of placement: it doesn't need a combustion air supply or flue gas extraction. You can therefore install it in a closed technical room, a closet, under the stairs, or anywhere with an electricity supply and a hydraulic connection to the heating system. The only requirement for the room is protection from frost (the boiler must not freeze) and adequate humidity levels (not outdoors, not exposed to the elements).

How long does the Vitotron last? What is its service life?

Viessmann is a premium manufacturer and its products are designed for a long service life. With proper installation, clean water in the system, and regular maintenance, you can expect a service life of 15–20 years. This is comparable to a gas condensing boiler, but the service costs of an electric boiler during that time are far lower.

Critical components in terms of service life:

Heating element – the most important component. With clean water and proper pressure, it will last the entire lifetime of the boiler.
Circulation pump – typically 10–15 years; after replacement, the boiler continues on. The pump is a standardized component and its replacement is relatively inexpensive.
Electronic controller – very reliable in normal operation; prone to failure only in the event of surge events (storms, grid outages). We recommend surge protection in the distribution board.
3-way valve (if equipped) – a moving part that may require lubrication or actuator replacement after years of operation.

Can I combine the Vitotron with solar photovoltaic panels?

Yes, and this is one of the most interesting current topics. An electric boiler is an ideal "consumer" of surplus energy from photovoltaics. If you have a solar system and export surplus power to the grid at a low feed-in price, it makes sense to use this surplus to heat water or provide heating via the Vitotron.

There are two basic approaches:

Intelligent control system – an energy manager (e.g. SolarEdge, Fronius Ohmpilot, or other third parties) monitors the PV system's output and household consumption. It redirects the surplus to the boiler. The Vitotron must be compatible with such a system via an output control input (0–10 V or relay inputs).
Simple thermostat/relay – a cheaper solution: when there is a photovoltaic surplus, a contact is activated that "turns on" the DHW tank. Not as elegant, but functional.

A real case from a project: A family house, 10 kWp photovoltaic system, Vitotron 100 up to 8 kW. In summer, the energy manager redirected an average of 3–4 kWh/day of surplus energy to the DHW tank and partly to the heating storage (underfloor heating). Result: the DHW tank was heated almost for free from PV surpluses from April to September in summer, with no extra electricity cost.

What servicing does the Vitotron require and how often?

One of the undeniable advantages of an electric boiler is minimal servicing burden. There is no legal obligation for an annual inspection as with gas. Nevertheless, we recommend:

Once a year: visual check of the system pressure (pressure gauge on the boiler), seal inspection, bleeding the radiators, checking the expansion vessel.
Every 2–3 years: professional servicing – inspection of the heating elements, inspection of the electrical connection, cleaning the filter on the return pipe.
As needed: replacement of the pump or the 3-way valve actuator in case of failure.

You can find much more information on this topic in the article Maintenance and servicing of the Vitotron electric boiler – what and how often.

Frequently Asked Questions (FAQ)

Can the Vitotron work without a pump – is the pump included with the boiler?

The Vitotron 100 has an integrated circulation pump – you don't need to buy an external one. The pump is continuously variable and controlled automatically by the boiler. For built-in installations with long pipe runs and large systems (over 120 m² of underfloor heating), an additional external pump may be needed in some circuits – this is assessed by a hydraulics designer.

What is the difference between the Vitotron 100 up to 8 kW and up to 24 kW in terms of installation?

Besides output and size, the key difference is in the power supply. The model up to 8 kW can, in some variants, be connected to a single-phase supply, while the model up to 24 kW always requires a three-phase supply of 3×400 V. For the model up to 24 kW, an appropriately sized circuit breaker (32–40 A) and a cable of at least 6 mm² Cu are also required. The Vitotron 100 up to 8 kW is more compact and quicker to install; the Vitotron 100 up to 24 kW requires more preparatory work on the electrical side.

What happens when there's a power outage? Does the Vitotron stop working completely?

Yes – an electric boiler doesn't work without electricity. This is its disadvantage compared to gas boilers with gravity circulation (although modern gas boilers also need electricity for the pump and electronics). If energy independence during outages is important to you, consider a backup source (UPS or a small generator) or a combination with a fireplace insert with a heat exchanger. However, for most apartment installations, this isn't a practically relevant issue – power outages in Slovakia are rare and short.

Is the Vitotron suitable for an old radiator system, or only for new installations?

You can connect the Vitotron to an old radiator system without major problems. It's important to thoroughly flush and clean the entire system beforehand (chemically or physically), so that impurities and sludge from the old boiler don't get into the new one. It's also necessary to check whether the water temperature required by the old radiators (55–75 °C) is within the range that the Vitotron can deliver – and yes, it can. A problem may only arise if the old system was designed for extremely high temperatures (80–90 °C, which is rare today), in which case the radiators may be undersized.

Do I need to use a special antifreeze mixture with the Vitotron?

It's not a requirement, but it's recommended in some cases. If there's a risk that the boiler won't be in operation during frosty periods (cottage, cabin, intermittent operation), an antifreeze mixture based on propylene glycol (not automotive ethylene glycol!) is a suitable protection. The Vitotron is compatible with a propylene glycol mixture, but the correct concentration must be used (usually 30–40%) and the manufacturer's instructions followed – some glycols reduce heat transfer and put more strain on the pump than plain water.

How long does installation of the Vitotron take and when can I start heating?

A standard installation with a prepared connection (electrics and hydraulics ready) takes 4–8 hours including the initial start-up and setup. If preparation of the electrical connection is also needed (new circuit breaker, cable), add 1–2 days of electrician's work. Once started up by an authorized technician, you can start heating immediately – no drying periods or special procedures are required (unlike new floor screeds, where the concrete needs to be heated up gradually).

Conclusion – what to take away from this article

Viessmann Vitotron electric boilers are technically advanced, reliable, and appropriately sized devices for modern heating – from small apartments through family houses to commercial buildings (where the EKCO.TM is more applicable). Key points to keep in mind:

Proper output sizing is essential – don't underestimate it, but don't be afraid of higher output either, the boiler will regulate itself.
The electrical connection must be addressed before any hydraulics – it's the longest link in the preparation chain.
If you also want to heat DHW, opt for the version with a 3-way valve and tank sensor.
Weather-compensated control and proper schedule settings are far more important for savings than the boiler type itself.
Regular basic maintenance extends the device's lifespan to 15–20 years without major expenses.

If you're unsure which model is right for you, read further articles in the Knowledge Center – specifically How to choose a Viessmann Vitotron electric boiler – what to focus on or Viessmann Vitotron vs. other electric boilers – what the comparison says. Choosing the right boiler is an investment for 15–20 years, so it's worth spending a little more time getting informed.

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'll be happy to help.