Protherm Tiger Condens vs. Thermona THERM vs. Vaillant ecoTEC: comparison of models with a tank
Protherm Tiger Condens vs. Thermona THERM vs. Vaillant ecoTEC: comprehensive comparison of condensing boilers with a built-in tank
If you are looking for a condensing boiler with a built-in domestic hot water tank, sooner or later you will come across three names that dominate the Central European market: Protherm Tiger Condens, Thermona THERM and Vaillant ecoTEC. Each of these manufacturers has decades of development behind them, a huge service network and – importantly for the customer – a genuinely different design philosophy. It's not just marketing. When you pick up the technical data sheet, measure the boiler in your boiler room, or compare behaviour during hot water usage peaks, the differences become very concrete.
In this article, we compare them objectively, with numbers, practical examples, and without declaring a winner in advance. Because the truth is, each of these boilers has situations where it is the best choice – and situations where a competitor clearly outperforms it.
Why have a tank inside the boiler at all – and why it matters for comparison
Before we dive into the comparison itself, it's important to understand exactly what we're comparing. A boiler with a built-in tank is a compact appliance where the domestic hot water tank is physically integrated into the boiler's casing. The whole thing hangs on one wall or stands on the floor, with one gas pipe, one power cable, one condensate drain. From an installation perspective, this is an elegant solution – especially in apartments, smaller houses, or anywhere there's no space or desire for a separate cylinder.
What differs between manufacturers is precisely how they design this tank: what volume they offer, how the tank is insulated, how quickly it heats up, what standby losses it has, and above all – how it behaves during simultaneous heating and hot water demand. This is exactly where the practical differences that customers experience every day are hidden.
You can find more about the selection philosophy in our article Condensing boiler with tank vs. boiler with external tank: which is more worthwhile, where we compare these two categories from a broader perspective.
Protherm Tiger Condens: a favourite with a strong service network
Protherm is well known to Slovak customers – it is manufactured in Skalica, which has a practical impact on the availability of spare parts and service technicians. The Tiger Condens range is among the best-selling boilers with a built-in tank in the Central European region, and not by accident. It is the result of many years of development, gradually refined by the manufacturer based on feedback from thousands of real installations.
In terms of the tank, Protherm offers two basic sizes: 21 litres and 42 litres. The smaller model is intended for single households or couples with lower hot water consumption, while the larger 42-litre one suits families with two bathrooms or households wanting higher comfort. Specifically:
- Protherm Tiger Condens 20/26 KKZ 21 – heating output 6–26 kW, 21 l tank, suitable for smaller flats and houses up to approx. 120 m²
- Protherm Tiger Condens 20/26 KKZ 42 – same output but with a larger 42-litre tank, for families with higher DHW demand
- Protherm Tiger Condens 30/35 KKZ 42 – higher output of 8–35 kW, 42 l tank, for larger houses or properties requiring higher heating output
The tank in the Tiger Condens is steel with an enamel coating and a single magnesium anode. Heat is transferred to the tank via a built-in coil-shaped heat exchanger. Heating the 42-litre tank at full output typically takes 15–20 minutes from a cold state, which is a realistic time comparable to competitors. The standby loss of the tank is stated at around 0.8–1.1 kWh/24h, which is an acceptable value for a boiler in this category.
What is most appreciated about the Protherm Tiger Condens in practice:
- Burner modulation range of 1:5 (e.g. from 6 to 30 kW) – the boiler doesn't switch on and off unnecessarily at low outdoor temperatures
- Simple, clear controls – a display with an intuitive menu, not rocket science
- Availability of service and parts – Protherm has a dense network of authorised service centres in Slovakia, an argument customers appreciate at the first sign of a fault
- Option to connect external controllers, including smart control – for example the Protherm Tiger Condens 20/26 KKZ 42 with an integrated smart controller
Where the Tiger Condens has certain limitations: the 42-litre tank is at the limit for families with four or more people if the house has only one bathroom and morning peaks are short. The boiler has no built-in solar input (unlike some competing models), which is an important detail for those considering future integration of solar collectors.
Thermona THERM: Czech construction with an emphasis on robustness
Thermona is a Czech company from Blansko with a long tradition and a strong position mainly in the Czech Republic and Slovakia. Their THERM range with a built-in tank (labelled THERM x KDZZ or similar abbreviations depending on the variant) differs structurally from Protherm in several significant respects.
Thermona traditionally emphasises construction robustness and serviceability. The boilers are designed so a technician can replace most components without unnecessarily disassembling the entire unit. Thermona tanks are typically available in volumes of 35 or 50 litres depending on the model – an important point when comparing to Protherm: Thermona offers a larger tank in its compact boilers, which larger families will appreciate.
The tank is enamelled, protected by a magnesium anode, and heating is achieved by direct connection of the tank to the primary heat exchanger circuit (not via an internal coil as with Protherm). This has the advantage of faster heating, but requires more precise hydraulics to prevent contamination of the heating circuit.
What installers highlight about Thermona:
- Larger tank in a compact design – 50 litres in a height dimension similar to competitors with 42 l
- Solar input as standard equipment in some models – a plus for future expansion
- Low operating noise – Thermona pays attention to noise levels and its boilers are among the quieter ones on the market
- Transparent technical documentation – installers appreciate the detailed manuals
On the other hand, Thermona has a slightly smaller network of authorised service centres in Slovakia than Protherm (which is a domestic manufacturer). This is not a disaster in the event of a breakdown, but for urgent service in a smaller town you may have to wait longer. Thermona's price is also historically slightly higher than Protherm for comparable parameters, which puts off some customers, although this alone is certainly not a reason to avoid it.
Vaillant ecoTEC: a premium class with ioniDetect and maximum comfort
Vaillant is a German manufacturer with over 150 years of history and a reputation for quality, which is also reflected in the price. The ecoTEC series with a built-in tank represents the pinnacle of what is technically achievable in this category – both in a good sense and in terms of the price you need to be prepared for.
The flagship model is the Vaillant VUI 26CS/1-5 ecoTEC plus IoniDetect with sensoComfort 720. What does the customer get for that higher price?
IoniDetect technology is one of the key differentiating features of Vaillant. Instead of classic ionisation ignition, the boiler continuously monitors combustion quality via ion analysis of the flame and dynamically adjusts the gas/air ratio. The result: the boiler works with maximum efficiency even as gas calorific value changes (which is common in practice), requires no mechanical combustion adjustment when the gas supply network changes, and maintains optimal NOx emission values over the long term.
SensoComfort 720 is an integrated smart controller with a touch display, a WiFi module and compatibility with the myVaillant app. This is a different league from a standalone external thermostat – the controller is directly included in the package, communicates with the boiler via an internal bus, and enables not only remote control but also predictive control based on weather forecasts and learned habits.
In terms of the tank, the Vaillant VUI offers a 46-litre integrated tank with polyurethane insulation. Tank heat losses are stated at below 0.7 kWh/24h, which is 20–30% less than typical competitors. In everyday operation this is not a huge difference, but over 10 years it adds up to a significant saving.
The tank is stainless steel (unlike the enamelled steel used by Protherm and Thermona). This is important: a stainless steel tank does not need an anode, no corrosion occurs at the higher temperatures of the disinfection cycle (typically 70 °C), and the manufacturer states a longer tank lifespan. On the other hand, a stainless steel tank is more sensitive to aggressive water with a high chloride content – in some areas of Slovakia it may be advisable to install a filter beforehand.
Another Vaillant bonus in practice: the boiler has a very low minimum flow temperature (around 25 °C), which allows efficient operation with underfloor heating without needing a mixing valve – in low-temperature systems this means further real fuel savings.
Technical comparison – table of key parameters
| Parameter | Protherm Tiger Condens KKZ | Thermona THERM KDZZ | Vaillant ecoTEC VUI |
|---|---|---|---|
| Heating output | 6–26 / 8–35 kW | 6–24 / 8–28 kW | 5–26 kW |
| Tank volume | 21 l / 42 l | 35 l / 50 l | 46 l |
| Tank material | Enamelled steel + Mg anode | Enamelled steel + Mg anode | Stainless steel |
| Tank heat losses | ~1.0 kWh/24h | ~0.9 kWh/24h | ~0.65 kWh/24h |
| Efficiency class (ErP) | A / A+ | A / A+ | A+ |
| Burner modulation | 1:5 (20–100%) | 1:4 (25–100%) | 1:6 (17–100%) |
| Integrated smart controller | Optional (extra) | No (external) | Yes (sensoComfort 720) |
| Solar input | No | Some models | Optional module |
| Approximate price | Mid-range | Mid-to-higher range | Higher-premium |
Real-life scenarios: where each boiler excels
Technical parameters are one thing, but customers buy a solution for their household, not a table of values. Experience from ten or more similar orders reveals several typical situations:
Scenario 1: Three-room flat in a panel building, two-person household
The flat has an area of 72 m², central heating via radiators, and the building's heat loss after insulation is around 4 kW. A 21-litre tank is fully sufficient – the couple showers one after another in the morning and doesn't run the dishwasher at the same time. Here, the Protherm Tiger Condens 20/26 KKZ 21 is the most sensible choice. A smaller tank means lower standby losses, the boiler is the cheapest of those compared, and service is available in every town. Vaillant would be unnecessarily expensive here. Thermona with a larger tank would only increase standby losses without any real benefit.
Scenario 2: Family house, 4 people, 2 bathrooms
A 150 m² house, heat loss of 8 kW, two bathrooms on different floors. Here the 42-litre tank reaches its limit – two morning showers in a row are still fine, but if a third person is added or a bath is taken instead of a shower, the tank may not be enough. In this case, Thermona with its 50-litre tank has a noticeable advantage. Or the Vaillant ecoTEC with 46 l plus faster heating thanks to better tank insulation. If the budget is tight, the Protherm Tiger Condens 30/35 KKZ 42 with higher output but the same tank size means faster reheating – in practice this compensates for the smaller volume.
Scenario 3: New low-energy building, owner wants a smart home
A 180 m² house, heat loss of only 5–6 kW thanks to passive features, underfloor heating, interest in remote control, the owner works from home and is focused on optimising operating costs. Here, the Vaillant ecoTEC with sensoComfort 720 is the clear choice. The wide 1:6 modulation range (from 17% output) is key for low-energy houses – a smaller boiler able to run genuinely long hours at low outputs achieves a real higher seasonal efficiency than a boiler with 1:4 modulation. The integrated smart controller with weather forecasting is not just a gimmick, but a real feature that, combined with good house insulation, saves noticeable money. A combination such as the Protherm Tiger Condens 20/26 KKZ 42 with a smart controller is also available if the customer prefers a lower entry price with similar functionality.
Scenario 4: Recreational cottage, irregular use
A 60 m² cottage, 6–8 visits per year, mostly weekends, sometimes a week in winter. Here the emphasis is on reliability and simplicity. The Protherm Tiger Condens in the smaller version is ideal: simple controls, a solid service network, and a reasonable price in case of a breakdown. Vaillant would be an investment that wouldn't pay off here – the premium smart controller features go unused with irregular use.
Hot water comfort: where the real differences are in everyday life
Tank volume is not everything. Reheat speed, standby loss, and behaviour during simultaneous heating and DHW demand also matter. You can find more on this topic in a separate article, How long does it take to heat water in a tank and what determines DHW comfort, in our Knowledge Centre.
In brief: at full boiler output (e.g. 26 kW) and a 42-litre tank, heating from cold water (10 °C) to a temperature of 60 °C takes approximately:
- Protherm Tiger Condens KKZ 42: ~16–20 minutes (depends on mains water temperature and settings)
- Thermona THERM 50 l: ~18–22 minutes (larger volume requires more energy)
- Vaillant ecoTEC VUI 26 CS 46 l: ~14–18 minutes (better thermal insulation = less loss during heating, plus a faster heat exchanger)
These differences are real, but in normal practice customers only notice them when the tank is empty and they have to wait. In a typical daily cycle, where the boiler regularly maintains the tank at temperature, comfort is comparable across all three.
Where they differ more significantly: standby losses. Over a year of operation (365 days):
- Protherm: 1.0 kWh × 365 = 365 kWh/year → at a gas price of €0.07/kWh ≈ €25.5/year in tank losses
- Vaillant: 0.65 kWh × 365 = 237 kWh/year → ≈ €16.6/year in losses
- Difference ~€9/year – over 10 years ~€90, which doesn't justify a much higher boiler price difference, but does contribute to the overall balance
Service, warranty conditions and availability of spare parts
This is a topic customers underestimate at the time of purchase, but it suddenly becomes very important after 3–5 years of operation. From a serviceability perspective in Slovakia:
Protherm has by far the densest network of authorised service centres in Slovakia – logically, since it is manufactured in Skalica and is part of the Vaillant Group (yes, Protherm and Vaillant are in the same holding company). Spare parts are available in most larger towns, usually within 24–48 hours. The standard warranty period is 2 years, extended to 5 years with online warranty registration and regular servicing by an authorised technician.
Thermona has a good service network in the Czech Republic; coverage in Slovakia is somewhat sparser. In larger cities (Bratislava, Košice, Žilina, Nitra, Banská Bystrica), authorised service is available, while outside them waiting times may be longer. Warranty conditions are the standard 2 years with an option to extend.
Vaillant has a well-developed service network and strong representation in Slovakia. The warranty period is up to 5 years if conditions are met (installation by an authorised technician, annual servicing). Since Protherm and Vaillant are part of the same holding company, in many areas of Slovakia one technician services both brands, which is a practical advantage.
You can read about common faults and their solutions in the article Common faults of condensing boilers with a built-in tank and how to solve them, which are clearly organised by error code and manufacturer.
Installation and placement requirements: practical differences
Before purchasing, it's important to verify that the boiler will physically fit into the planned space and that supply requirements are met. You can find a detailed procedure in the article Installing a condensing boiler with a built-in tank: procedure and requirements.
In terms of dimensions: all three brands offer compact designs, but the tank always increases the height or width of the boiler compared to a tankless variant:
- Protherm Tiger Condens KKZ: height 1,080–1,130 mm depending on model, width 450 mm, depth 350 mm – typically suitable for a standard utility room as well as fitting into a kitchen unit provided a flue outlet is available
- Thermona THERM KDZZ: height 1,100–1,200 mm depending on tank size, width 480 mm – somewhat larger, but not dramatically so
- Vaillant ecoTEC VUI: height around 1,160 mm, width 500 mm – slightly larger, but compensated by better tank insulation
All three boilers are wall-mounted and require a condensate drain to the sewer, a flue outlet (coaxial or separate pipes depending on configuration), a gas connection, and a 230 V power supply. The minimum inlet water pressure should be at least 1.5 bar, ideally 2.5–4 bar.
An important note on warranty conditions: all three manufacturers require installation by an authorised installation technician. Self-installation is not illegal, but it voids the manufacturer's warranty and can also be problematic from a property insurance perspective.
Price, operating costs and overall investment economics
Customers usually ask about the boiler's price, but the real question is: how much does the boiler cost over 10 years of operation? The total cost includes: purchase price + installation + annual servicing + energy + any repairs.
Approximate figures (excluding installation, VAT included):
- Protherm Tiger Condens KKZ 42 (26 kW): entry price in the mid-range segment, available variants, low servicing costs thanks to a dense network
- Thermona THERM KDZZ 50 l: slightly higher entry price than Protherm, but a larger tank at no extra charge
- Vaillant ecoTEC VUI with sensoComfort 720: higher entry price (the smart controller is included in the price, which should be factored in), but lower standby losses and wider modulation can reduce annual gas consumption by 5–10% compared to competitors in low-energy houses
If we calculate for a low-energy house with gas consumption of 8,000 kWh/year and a price of €0.07/kWh, an 8% saving thanks to Vaillant's better modulation and control means an annual saving of ~€44. Over 10 years, ~€440. Vaillant's entry price premium over Protherm is usually €300–600, so in a low-energy house the investment can pay off. In an older house with poor insulation, where the boiler runs at full output for most of the heating season, this difference is much smaller.
You can find more about choosing the right output in the article What output of condensing boiler with a tank is enough for my house, where you will also find specific calculation methods.
Frequently Asked Questions (FAQ)
Is it worth paying extra for a Vaillant ecoTEC over a Protherm Tiger Condens?
It depends on the situation. In a low-energy or passive house, where you need maximum modulation and smart control, Vaillant brings real measurable savings and a long-term benefit. In a standard insulated house with normal consumption, the difference is much smaller, and Protherm offers an excellent price/performance ratio with excellent service availability in Slovakia. If a stainless steel tank without an anode and a standard integrated smart controller are important to you, Vaillant has those advantages without question.
What is the difference between a 21 l and 42 l tank in the Protherm Tiger Condens?
A 21 l tank is sufficient for 1–2 people taking showers, without accounting for baths or simultaneous demand in two places. A 42 l tank is intended for 3–4 people or households wanting higher comfort – baths, two bathrooms, a dishwasher. If there are more people in the house or you prefer greater comfort, it's worth opting for the 42-litre variant. Standby losses are higher by roughly 0.2 kWh/day, which amounts to a few euros a year – negligible compared to the comfort gained.
Can a boiler with a built-in tank be connected to solar collectors?
Not directly with the Protherm Tiger Condens – the tank in this boiler is not equipped with a solar coil. Thermona offers models with a solar input, and Vaillant allows solar expansion via a compatible module. If you're planning solar collectors, either choose a boiler with direct solar compatibility or consider a two-boiler system (condensing boiler + solar tank). More on this topic is covered in the article Condensing boiler with tank vs. boiler with external tank: which is more worthwhile.
How often does the magnesium anode in an enamelled tank need to be replaced?
The anode should be checked at every annual service inspection and typically replaced every 2–4 years depending on water quality. In areas with soft water (low mineralisation), the anode is consumed faster; with hard water, more slowly. Neglecting anode replacement leads to tank corrosion and potential failure before the end of the boiler's lifespan. Vaillant, with its stainless steel tank, doesn't have this problem – no anode needs replacing, but water quality in terms of chloride content should be monitored.
Is Thermona less reliable than Protherm or Vaillant?
No. Thermona has a good reputation for long-term reliability – installers in the Czech Republic and Slovakia appreciate their robust construction and easy serviceability. The main difference is not in reliability, but in the density of the service network in Slovakia (Protherm and Vaillant have denser coverage) and in the availability of certain special features. If you're in a city with available Thermona service, there's no reasonable reason to avoid it.
Can I control a boiler with a built-in tank via my phone?
Yes, all three manufacturers allow this – with varying degrees of integration. The Vaillant ecoTEC with sensoComfort 720 has WiFi and the myVaillant app included directly in the package. Protherm offers a smart controller as an optional add-on – for example, the Protherm Tiger Condens 20/26 KKZ 42 with a smart controller is a ready-made single-source solution. Thermona uses external controllers with WiFi functionality that need to be purchased separately. More details on intelligent control can be found in the article Frequently asked questions about condensing boilers with a built-in tank.
Conclusion: how to decide
Protherm Tiger Condens, Thermona THERM and Vaillant ecoTEC are three qualitatively different answers to the same question: how to combine heating and hot water preparation in one appliance. None of them is bad. All three are condensing boilers with efficiency above 96%, all meet ErP requirements, and all have a long track record in this category.
The decisive criteria when choosing are: the number of people and their hot water usage habits (→ tank size), the building's energy standard (→ modulation and control), service availability in your area, your purchase budget, and plans for further system expansion (solar, smart home). Our accompanying articles in this category can help you answer these questions – for example, What tank volume do I need for my house or How to choose a condensing boiler with a built-in tank: what to look out for.
If you're not sure about a specific model, the easiest way is to provide the parameters of your property (area, heating type, number of people) and let our experts
Do you have a question on this topic?
Can't decide or dealing with a specific situation in your household? Write to us - we'll be happy to help.