Euroster 813 Solar vs. ZPS control units: comparison of functions and applications
Euroster 813 Solar vs. ZPS control stations: complete comparison of features and applications
When I first met a customer who couldn't decide whether to buy a simple differential thermostat or a more complex control station for a solar system, it took me about an hour to reach the right conclusion together. It wasn't due to his lack of understanding – on the contrary, the problem was that these two product categories look very similar at first glance, but in reality they address different situations and have diametrically different configuration options. Today I want to thoroughly explore this topic – with specific numbers, real-life scenarios and clear recommendations on when to choose which solution.
The basic question is clear: you have a solar system for heating hot domestic water (HDW), possibly with heating support, and you need control. You basically have two types of devices to choose from – a differential thermostat in the form of Euroster 813 Solar and control stations of the ZPS series, specifically ZPS 6, ZPS 16 or ZPS 28. The differences are significant and we will go through them systematically in the following sections.
What is Euroster 813 Solar and how it works
Euroster 813 Solar is an electronic differential thermostat primarily designed for controlling a solar system with one circuit – that is, one collector or a group of collectors connected to one storage tank. Its principle of operation is elegantly simple: it measures the temperature at the collector (sensor T1) and the temperature in the storage tank (sensor T2). If the difference between these two values is greater than the set differential temperature (typically 5–10 °C), the controller starts the circulation pump. When the difference decreases below the set-off differential temperature (typically 2–4 °C), the pump stops.
This logic is the basis of the entire solar control – nothing more, nothing less. Euroster 813 Solar implements it reliably, with sufficient configurability of basic parameters. It has a display, the option to set the maximum tank temperature (protection against overheating), the minimum collector temperature (protection against reverse flow at night), and of course both differential temperatures for switching on and off.
From an installation point of view, it is a compact device on a DIN rail (or wall mounting according to the version), which does not require any special knowledge beyond basic electrical wiring. 230 V power supply, pump output (relay), two input sensors – and that's all. For a simple solar system with one storage tank, this is sufficient and does not unnecessarily complicate the situation.
What are ZPS control stations and what additional features they offer
ZPS control stations are a different category. They are not just controllers – they are complete hydraulic and control units that integrate multiple functions at once. They include not only control electronics (differential thermostat), but also other components: a circulation pump (built directly into the station), a flow meter with the ability to read flow, thermometers on the supply and return pipes, a safety valve, a bleed valve, a check valve and a shut-off valve for setting the flow. The entire assembly is integrated into one compact cabinet device that is easily connected to the solar circuit.
The number in the name – ZPS 6, ZPS 16 and ZPS 28 – refers to the maximum flow in liters per hour or (depending on the version) to another performance parameter. ZPS 6 control station is suitable for smaller systems, typically 2–4 flat collectors, ZPS 16 covers medium-sized installations and ZPS 28 is intended for larger commercial or family systems with multiple collectors. A more detailed analysis of dimensioning can be found in the article How many collectors can the ZPS 6, ZPS 16 and ZPS 28 control station handle.
Comparison of features step by step
To be specific, I have prepared an overview of key parameters and features where these two solutions differ. This table is based on real installation experience – not on marketing brochures.
| Function / parameter | Euroster 813 Solar | Control station ZPS |
|---|---|---|
| Differential thermostat | ✔ yes | ✔ yes |
| Integrated circulation pump | ✘ no | ✔ yes |
| Integrated flow meter | ✘ no | ✔ yes |
| Integrated safety valve | ✘ no | ✔ yes |
| Temperature sensors supply/return loop | ✘ no | ✔ yes |
| Loop air vent | ✘ no | ✔ yes |
| Number of sensors (T-inputs) | 2 | 2–3 (depending on version) |
| Maximum collector temperature protection | ✔ adjustable | ✔ adjustable |
| Maximum storage tank temperature protection | ✔ adjustable | ✔ adjustable |
| Night cooler (heat dump) | ✔ yes (in case of overheating) | ✔ yes |
| Power counter / kWh | ✘ no | ✔ yes in versions with flow meter |
| Volume of solar medium | external pump (0.5–3 collectors) | built-in pump (2–8+ collectors) |
| Price / installation complexity | lower / simpler | higher / requires professional installation |
| Compactness of the solution | controller + separate components | everything in one box |
Practical scenarios: when to choose which solution
Scenario 1: Family house, 2 collectors, one 300 L storage tank
This is the most common case I encounter. The owner wants to save on hot water heating for a family of four, has two flat collectors on the roof, a storage tank in the boiler room, and existing piping from previous owners. The installer is a friend, not a solar specialist.
In such a case, the Euroster 813 Solar can be completely sufficient – provided that other hydraulic components (pump, safety valve, air vent, expansion vessel) are solved separately in the setup. Advantage: lower price, simpler electrical installation. Disadvantage: you have to buy and install each component separately, which with a non-professional approach can lead to errors (e.g., forgotten air vent, undersized expansion vessel).
On the other hand, the control station ZPS 6 is an elegant solution in this scenario – you get everything you need in one package, with a hydraulically verified setup. Installation takes less time and the risk of error when assembling is minimal. The additional cost compared to a standalone controller is returned in the time saved during installation and the certainty that the system is hydraulically correctly assembled.
Scenario 2: Larger house, 6 collectors, two storage tanks in cascade
Here the answer is clear: control station. The Euroster 813 Solar is not dimensioned for such a setup – it does not have an output for the second storage tank, nor the possibility to control a switching valve for the cascade, and the pump group outside the cabinet would be more hydraulically demanding to assemble at such a performance level. The control station ZPS 16 or ZPS 28 is the right choice here, with the choice between them depending on the hydraulic parameters of the system – precise dimensioning is the subject of a separate article How many collectors can the ZPS 6, ZPS 16 and ZPS 28 regulation handle.
Scenario 3: Renovation, existing pump and hydraulics are preserved
This is an interesting case. The customer has an old solar system, the hydraulics are complete and functional (correct pump, safety valve, expansion vessel), only the aging controller needs to be replaced. Here, the Euroster 813 Solar makes excellent sense – there is no reason to replace the entire setup with a control station. It is enough to replace the controller, connect the existing sensors (or add new ones), and the system continues to run. The cost of renovation is minimal, the result the same.
Scenario 4: New construction, investor wants to measure performance
In a new construction, where the investor (or a grant project) requires measurement of the actual performance of the solar system in kWh, the control station ZPS with an integrated flow meter and temperature sensors for the supply/return loop is a necessity. The Euroster 813 Solar simply does not have this function – it only measures temperatures on the collector and storage tank, not the actual heat delivered to the system. If you need a report on solar yields (e.g., for green certificates or bank financing), the choice is clear.
Differential control logic – detailed comparison
Both systems operate on the same physical principle of a differential thermostat, but the implementation has differences that are often overlooked in a superficial comparison.
The Euroster 813 Solar allows setting the following parameters:
- ΔT for turning on (typically adjustable from 2 to 20 °C) – the difference T_collector – T_tank at which the pump is started
- ΔT for turning off (typically 1–10 °C) – hysteresis for pump shutdown
- Maximum tank temperature (overheat protection, e.g. 85 °C) – when this value is reached, the pump is stopped regardless of the differential temperature
- Maximum collector temperature – protection against too hot a medium entering the tank (e.g. 120 °C)
- Minimum collector temperature – protection against night return flow (the pump will not start if the collector is cooler than the tank by more than the set value)
- Night cooling function – if the tank exceeds a critical temperature, the system activates the pump at night to transfer heat from the collectors to the air
Control stations ZPS have an equivalent or even more advanced configuration of the differential thermostat – plus they additionally monitor the actual flow and temperatures on the supply and return pipes, which allows for the calculation of thermal power (Q = m·cp·ΔT). This function is very valuable for system diagnostics: you not only see that the pump is running, but also how much heat is actually being delivered.
A detailed guide on setting differential values can be found in the article Setting differential temperature in solar regulation: how to properly configure switching – this topic is thoroughly discussed there, including tips for different types of collectors and storage tanks.
Electrical installation and practical mounting
From the perspective of electrical installation, the Euroster 813 Solar is simpler: it is a standalone device that you power from the 230 V grid, connect the relay output to the pump, and connect two sensor inputs. The entire wiring fits into one DIN cover or directly into the boiler cabinet. With experience, I estimate the installation time to be 45–90 minutes including testing.
The control station ZPS is a different matter. It is a cabinet with integrated hydraulics – it is mounted on the wall of the boiler room (usually with a hanging system that is part of the delivery), the two branches of the solar circuit (supply and return) are connected to it, 230 V power is supplied for the built-in pump, and sensor wires are connected. The installation itself takes longer, but the result is much cleaner – no loose pipes and components scattered throughout the boiler room.
An important detail from practice: when installing ZPS stations, it is necessary to pay attention to the correct direction of media flow – the station is designed with a defined inlet and outlet, swapping them will cause malfunction or damage to the check valve. Tips for error-free wiring can be found in the article Mounting solar system regulation: connecting the pump, sensors, and expansion tank.
Integration with water heater and TÚV storage tank
Both systems assume connection to a storage tank (water heater) with a heat exchanger or with a direct input of the solar circuit. The basic principle is the same: the tank temperature sensor (T2) must be placed in the lower third of the tank – it is precisely there that the coldest water is measured, which is crucial for the correct differential logic. If you were to place the sensor higher (in the warmer zone), the controller would wrongly assume that the tank is warmer than it actually is, and the pump would start later or not at all.
The Euroster 813 Solar does not have the function of controlling the electric heating of the tank – its role is exclusively to control the solar circuit. If you want the controller to also manage the electric heating element in the tank as a backup (e.g., when the sun is not enough), you need either an external tank thermostat or a more complex system. Many ZPS control stations integrate this option or allow for easy addition of a module.
A more detailed connection with various types of storage tanks is described in the article How to connect solar system regulation with a water heater or TÚV storage tank.
Price, service and long-term costs
The price of the Euroster 813 Solar is significantly lower than the price of any ZPS control station. That is a fact. But the calculation changes when we take into account the total installation costs. The Euroster 813 Solar requires the addition of all hydraulic components separately – a pump (for the solar circuit, not a standard one, but one resistant to glycol medium and high temperatures), a safety valve set to the correct pressure (usually 6 or 10 bar), a degasser (best automatic, but with the possibility of closing under pressure), a check valve, a pressure gauge, and a shut-off valve. If you buy these components separately from different manufacturers, the total quickly approaches or even exceeds the price of a complete ZPS station.
Moreover, the installation of disparate components from different suppliers is more time-consuming and requires greater attention to detail (pressure classes, dimensional compatibility, material resistance to glycol mixtures). With a ZPS station, the manufacturer has already solved these issues for you – the components are mutually compatible, tested as a whole, and the warranty covers the entire assembly.
From a service perspective: the Euroster 813 Solar is simple to diagnose – if it fails, the causes are limited (controller, pump, sensor). A ZPS station has more components, but at the same time it has a built-in flow meter and thermometers, which in turn simplifies diagnostics during operation: you can see what is happening without the need to attach external probes. The article Common faults in solar regulation: error messages, pump failures and inaccurate sensors describes typical problems of both types of regulation in detail.
Seasonal maintenance and inspection
Both systems require similar regular inspections: condition of sensors, hydraulic tightness, pump functionality, and condition of the solar medium (glycol concentration, pH). For ZPS control stations, it is also necessary to check the cleanliness of the built-in flow meter (impurities in the medium can reduce its accuracy) and the condition of the automatic degasser (sealing, possible corrosion of the seat). Specific procedures before and after the heating season are described in the article Maintenance and inspection of solar regulation: what to check before and after the heating season.
In practice: with systems using the Euroster 813 Solar, customers tend to forget to check the condition of the pump a bit more often, since it is not visually part of the "regulation cabinet". With a ZPS station, the pump is directly in the cabinet – during a routine inspection, you have the entire hydraulic system in front of you and nothing is overlooked.
Most frequently asked questions (FAQ)
Can I use the Euroster 813 Solar with tubular (vacuum) collectors, or only with flat ones?
Yes, the Euroster 813 Solar works with any type of collector – flat or tubular (CPC or heat-pipe). What is important is the correct placement of sensor T1: on the outlet nozzle of the collector for flat collectors, and on the manifold for tubular (heat-pipe) collectors. Tubular collectors reach higher temperatures, so it is important to set the maximum collector temperature to a higher value (typically 130–150 °C) than for flat ones (80–100 °C) – otherwise the controller would unnecessarily block the pump at normal operating temperatures.
Is a ZPS control station always better than the Euroster 813 Solar?
No – it depends on the situation. In renovations with an existing functional hydraulic system, in small systems with 1–2 collectors and a simple storage tank, or in projects with a limited budget where other components are already available, the Euroster 813 Solar may be a better choice in terms of cost and simplicity. A ZPS control station is unmatched in new constructions, larger systems, when you need performance measurement or want to have the entire hydraulic system neatly in one cabinet.
Can I connect two pumps to the Euroster 813 Solar (e.g., for a dual-tank system)?
No, the Euroster 813 Solar has only one relay output for one pump. For systems with two storage tanks or two circuits (e.g., collector → storage TÚV + collector → floor heating), you need either a controller with multiple outputs or a connection via an external switching valve (3-way motor valve) controlled by an external thermostat. This solution is more complicated in terms of wiring – consider a control station with the appropriate function instead.
What happens if I forget to fill the solar medium and start the regulation with empty pipes?
Dry running is critical for the circulation pump – most circulation pumps for solar circuits are lubricated by the medium they pump. Without medium, overheating of the bearings and pump damage will occur within minutes. Some ZPS control stations have protection via a pressure sensor (the system starts the pump only when sufficient pressure of the medium is present in the circuit), but not all versions. Therefore, always check the filling and degassing of the solar circuit before the first start – the procedure is described in detail in the article Installation of solar system regulation: connecting the pump, sensors and expansion tank.
What medium should I use in the solar circuit and does it affect the choice of regulation?
Standardly, a glycol-water mixture (propylene glycol or ethylene glycol) with corrosion inhibitors is used, with a concentration according to the required frost protection – typically 30–40 % glycol for protection down to –15 to –20 °C. The type of medium does not directly affect the choice between Euroster and ZPS station, but it does affect the material compatibility of components (copper, brass, stainless steel – yes; aluminum without special inhibitors – caution). Both systems are designed for operation with glycol medium; it is important not to use standard automotive antifreeze mixtures – these contain silicates that react with copper heat exchangers.
How long does it take for solar regulation to pay for itself in energy savings?
With average Slovak solar irradiation (about 1,000–1,200 kWh/m² annual solar radiation), a typical efficiency of a flat collector of 40–60 %, and an electricity price of around 0.20–0.25 €/kWh, the payback period of the regulation alone (without collectors and storage tank) is in the range of 1–3 years. Regulation is the cheapest part of the entire system – collectors and storage tanks have a much longer payback period (8–14 years for the entire system), but the total investment makes economic sense when properly designed, even without subsidies.
Conclusion: how to decide without unnecessary guesswork
After years of experience with solar regulation, I have a simple decision tree: if you are starting from scratch (new installation, new storage tank, new piping) – you choose a ZPS control station, because the completeness of the solution and the clarity of the entire hydraulic system outweigh any price difference. If you are only replacing the regulator in an existing system with a functional pump and hydraulic system – go for the Euroster 813 Solar. It is a reliable, straightforward differential thermostat that does its job without unnecessary complexity.
If you are unsure which option is right for your specific system, I recommend reading other articles in this section – especially How to choose regulation for a solar system: differential thermostat vs. control station and How to choose regulation for a solar system: what to watch out for, where additional criteria are discussed (number of collectors, type of storage tank, monitoring requirements, etc.).
Good regulation is the heart of every solar system. A collector without good regulation is like an engine without a control unit – it may work, but never at full potential. Choose wisely and your system will reliably serve you for decades.
Do you have a question about this topic?
Can't decide or are you dealing with a specific situation in your household? Write to us – we are happy to help.