Frequently Asked Questions about Grundfos Pumps
Common questions about Grundfos pumps – expert answers from practice
Grundfos is among the most commonly mentioned brands when customers talk about circulation pumps or water pumps. Over the years of practice, we have encountered hundreds of recurring questions – some are simple and can be solved in a few sentences, while others require a thorough technical analysis. In this article, we have sorted them into thematic categories so that you get complete answers instead of vague "it depends on the situation". Read on until you find your question – and if you need to dive deeper into a specific topic, we also have separate articles in this Knowledge Centre for you.
1. Why Grundfos and not a cheaper alternative?
This is the number one question on most orders. The customer sees a price offer, compares it with an unknown brand for a third of the price, and wants to know why to pay more. The answer is not marketing – it is engineering.
Grundfos has been operating since 1945 and is today one of the three largest pump manufacturers in the world. Their production tolerances, hydraulic testing, and motor lifespan are documented and verifiable. Specifically: the UPS series circulation pumps are designed to last 10 to 15 years with proper installation. Their energy efficiency class A meets the European ErP 2015 standard. A cheaper alternative without this certification can consume up to 3× more electricity annually – with 24/7 operation, this means an additional 60 to 120 euros on electricity every year. Over 10 years, this exceeds the price difference at the time of purchase.
Another practical aspect: Grundfos has a service network and spare parts available throughout Europe. If your circulation pump from an unknown manufacturer fails in January during freezing weather, you may encounter a problem that the spare part is not available anywhere within a 200 km radius. This does not happen with Grundfos.
2. What is the difference between UPS, MAGNA, CM and UNILIFT pumps?
Grundfos has an extensive range of products, and customers are often confused by it. Each series has its specific application – mixing them would be a mistake. Here is an overview of the most important ones:
- UPS (e.g. UPS 25-30, UPS 25-40, UPS 25-60): Classic circulation pumps for heating systems. Three-speed switch, fixed speed. Ideal for standard central heating layouts in houses and apartments. Today, they are among the most widespread on the Slovak market.
- MAGNA3: Premium series with a frequency converter and automatic control. The pump adjusts itself to the current system demand – it consumes only as much energy as needed. Suitable for new builds and renovations where you want to minimize operating costs.
- Solar (e.g. Solar 15-80 or Solar 25-120): Special pumps for solar thermal systems. They handle high temperatures of the heat transfer fluid (typically 110 °C and more) and are designed for glycol mixtures. More about this series can be found in the article Grundfos solar pumps – what they are used for and how they work.
- UNILIFT KP: Submersible water pumps – for example, from flooded basements, construction pits, or garden ponds. These are not circulation pumps, but discharge pumps. We will discuss the UNILIFT series in more detail below.
- CM / CME: Centrifugal pumps for industry and public buildings. They are not relevant for the owner of a family home.
3. Questions about circulation pumps UPS – selection, installation, operation
3.1 Which UPS model should I buy for my house?
The most common mistake is that the customer comes with the question "I want a UPS 25-40, is that correct?" without knowing the basic parameters of their system. The numbers in the name are not random – the first number (25) indicates the diameter of the connecting flange in millimeters, the second number (e.g. 30, 40, 60, 80) expresses the maximum pumping head of the pump in tenths of a meter, i.e. 40 = 4 m, 60 = 6 m.
For a typical family house with central heating on an area of 100 to 150 m², a GRUNDFOS UPS 25-30 is usually sufficient at medium or higher speed. For a house with 150 to 250 m² or with a larger number of radiators and longer piping, the UPS 25-40 or UPS 25-60 model is more suitable. Three parameters are decisive: boiler power (kW), total hydraulic resistance (pressure loss) of the piping, and required flow. A more detailed calculation process can be found in the article What Grundfos pump power do I need for my house.
3.2 What does it mean if the circulation pump is constantly running at third speed?
If you have to constantly switch to the third (highest) speed for the system to function at all, it indicates either an undersized pump or a hydraulic problem in the system – most commonly clogged filters, narrowed supply pipes, air in the system, or incorrectly adjusted balancing valves. A pump running at third speed consumes 40–60 % more energy than at second speed, and it also wears out faster. The solution is not to buy a larger pump, but first to inspect the system.
3.3 Can I install the circulation pump UPS vertically?
Yes, UPS pumps are designed for horizontal mounting (the rotor shaft lies horizontally), but vertical mounting is possible provided the motor points upward – not downward. If the motor points downward, the bearings would not be properly lubricated and the service life would be significantly reduced. The detailed installation procedure can be found in the article Mounting a circulation pump Grundfos step by step.
4. Questions about Grundfos Solar pumps
4.1 Can I use a standard circulation pump UPS in a solar circuit?
Technically, it will work for a few months, but it is not a correct solution and will eventually lead to failure. A solar collector circuit operates with a glycol mixture at temperatures that can exceed 140 °C in stagnation. Standard UPS pumps have seals and lubricants designed for a maximum of 110 °C with clean water. At higher temperatures, the seals degrade, the glycol mixture based on propylene glycol attacks inappropriate materials, and the pump will eventually burn out or start leaking.
Special solar pumps – for example, GRUNDFOS Solar 25-120, 180 mm or GRUNDFOS Solar 15-80, 130 mm – have special seals resistant to glycols and temperature-stable lubricants. These are structural differences not visible from the outside, but crucial for trouble-free operation. The number in the name (15 or 25) again indicates the throat diameter (G 1" or G 1½"), the second number the maximum head, and the third number the construction length (130 or 180 mm). A comparison of both models can be found in the article Grundfos UPS vs. solar pumps Grundfos – which one is suitable for your system.
4.2 What is the correct flow rate in a solar circuit?
The recommended flow rate ranges between 0.6 and 1.2 liters per minute for each square meter of collector area. For a standard residential solar system with 2 collectors (total area approx. 5 m²), the flow rate is 3 to 6 l/min. The model Solar 15-80 can handle this range in 99 % of standard residential installations. The model Solar 25-120 is intended for larger systems – for example, 8 to 12 collectors on a larger residential house, a guesthouse, or in combination with a storage tank over 500 liters.
5. Questions about UNILIFT KP pumps – water pumping
5.1 What is the difference between models KP 150 A1 and KP 250 A1?
Both models are submersible pumps designed for pumping contaminated water with small impurities (up to 5 mm in diameter for KP 150 A1, or 10 mm for KP 250 A1). The key difference lies in performance and maximum flow rate:
- GRUNDFOS UNILIFT KP 150 A1 – power 150 W, maximum flow rate approx. 7 200 l/h (120 l/min), maximum head 5 m. Suitable for pumping garden floods, smaller flooded basements (up to 60–70 m²), or as a permanent pump in a drainage pit.
- GRUNDFOS UNILIFT KP 250 A1 with 10 m cable – power 250 W, maximum flow rate up to 12 000 l/h (200 l/min), maximum head 8 m. For larger floods, deeper pits, or situations where water needs to be pumped over a greater distance or height.
The 10 m cable version of the KP 250 A1 is particularly useful when there is no socket nearby – for garden work, construction sites, or remote basements. The KP 150 A1 has a standard 5 m cable, and if a longer cable is needed, a suitable extension cable with a minimum cross-section of 1.5 mm² for 230 V should be used.
5.2 Can the UNILIFT KP pump run dry?
No. The motor is cooled by the pumped water. If the pump runs without water, the motor overheats and after a few minutes (sometimes even faster), the winding is damaged. Therefore, when using automatic control with a float switch, ensure correct settings – the float should switch off the pump before the water level drops below the inlet edge. A detailed installation and connection procedure for UNILIFT pumps is described in the article How to connect a Grundfos UNILIFT pump – installation steps.
5.3 Can the UNILIFT KP be used to pump drinking water?
No. Pumps of the UNILIFT KP series are designed for waste, drainage, and grey water. For pumping drinking water, special series are intended (e.g., Grundfos SQ/SQE for wells or CM for household water supply). Using UNILIFT pumps in a drinking water system could cause contamination due to materials not certified for contact with drinking water.
6. Questions about faults and service
6.1 The pump is running, but the radiators are cold – what is the problem?
This is one of the most common service cases. The motor is running (you can hear it humming), but water is not flowing. There are several possible causes, and diagnosis is carried out step by step:
- Pump airlock: Air in the hydraulic part prevents flow. Solution: bleed the pump using the bleed screw (a small brass screw on the side of the pump body). Turn it half a turn, wait until water flows out without bubbles, then tighten it again.
- Stuck rotor: After the first start-up after a summer break, the rotor may be blocked by deposits. Turn off the power, turn the shaft with a screwdriver (slot on the front of the rotor), and turn it on again.
- Clogged filter: The mesh filter before the pump is clogged. It needs to be cleaned.
- Capacitor or winding fault: The motor is running, but with very low efficiency. This requires current measurement and professional intervention.
A detailed diagnostic procedure is described in the articles Grundfos pump is not pumping or humming – causes and solutions and Common Grundfos pump faults and how to fix them.
6.2 How much does Grundfos pump service cost and is it worth repairing?
For circulation pumps of the UPS 25-30 or UPS 25-40 class (retail price 40–80 €), repair is usually not worth it. The cost of labor and parts is comparable to or exceeds the cost of a new unit. For premium models such as MAGNA3 (price 200–400 €) or large UNILIFT models (150–250 €), repair may be worth it if the fault is identifiable and involves standard parts (seal, capacitor, float switch).
Preventive maintenance is cheaper than repair – what exactly to check is described in the article Grundfos pump maintenance and service – what to check every year.
7. Questions about energy consumption and savings
7.1 How much electricity does a circulation pump consume?
An old type of circulation pump without regulation (e.g., from manufacturers from the 90s and 00s) consumes 60 to 100 W continuously. Over a 7-month heating season (210 days × 24 hours), this amounts to 302 to 504 kWh per year. At an electricity price of 0.18 €/kWh, the annual cost is 54 to 91 €.
Modern Grundfos UPS pumps (with energy class A) typically consume 45–65 W at medium speed. Even more efficient models with an EC motor, such as MAGNA3, consume 5–25 W according to the current system demand – this is 2 to 10 times more efficient than older pumps. The return on investment for replacing with MAGNA3 is usually 3 to 5 years.
7.2 Is it beneficial to run the circulation pump 24/7 or to turn it off at night?
In systems with radiators without thermostatic heads, continuous operation is standard. In modern systems with thermostatic heads or with an intelligent boiler controller, limiting the flow at night can bring 10–15 % energy savings. Most Grundfos MAGNA3 pumps can be connected to external control (0–10 V signal or Grundfos GO app) and night-time throttling can be set automatically. This is not possible with UPS pumps without an external timer relay.
8. Technical specifications and compatibility
8.1 How do I read the Grundfos pump type label?
You will find these key values on the label: rated voltage (230 V or 400 V), power consumption (W or kW), maximum pressure (bar), maximum fluid temperature (°C), connection dimensions (e.g. G 1½" or DN 32), and energy class (A, B, C). Based on these values, you can verify whether the pump is suitable for your system or compare it with design specifications.
8.2 What is the maximum working pressure of UPS pumps?
Standard Grundfos UPS pumps have a maximum working pressure (PN) of 10 bar. In a typical heating system of a family house, the working pressure is 1–1.5 bar, so you have a large reserve. Pressure problems occur only in high-rise buildings (8 or more floors) or in industrial applications – in these cases, special models with higher PN are required.
8.3 Can I connect a Grundfos pump directly to a solar photovoltaic panel without the grid?
Standard Grundfos UPS and Solar pumps are designed for alternating current 230 V / 50 Hz from the grid. Direct power supply from a PV panel without an inverter is not possible – the panel provides direct current with a variable value. The solution is to use a special DC pump (e.g. Grundfos SQFlex or Lorentz), or a standard AC pump with a DC-to-AC inverter. For garden solar pumps (fountains, ponds), there are cheaper DC solutions from other manufacturers.
9. Installation and compatibility with boilers and systems
9.1 I have an external circulation pump – some boilers have built-in ones. When do I need an external one?
Modern condensing boilers (Vaillant ecoTEC, Viessmann Vitodens, Baxi, Protherm Panther) have built-in pumps sized for an average house. You need an external pump in these situations:
- Your house has a large area (180+ m²) and extensive piping, where the built-in pump cannot provide sufficient flow in distant circuits.
- You have a system with multiple circuits (heating, floor heating, DHW tank) – each circuit needs its own pump via a manifold.
- An older boiler without a built-in pump (e.g. old gas boilers or solid fuel boilers).
- Solar circuit – always requires a separate solar pump.
9.2 Do I need to replace the pump when replacing an old boiler with a condensing one?
Not necessarily, but we recommend considering it. Condensing boilers operate with low temperature differentials (55/45 °C or even 45/35 °C), which means higher flow at the same output. If your old pump is sized for a classic differential of 90/70 °C, it may not provide sufficient flow with a new condensing boiler. At the same time, it makes sense to replace a 10–15 year old pump with an energy-efficient one during renovation – the investment in a new Grundfos UPS or MAGNA3 will pay back in saved electricity.
10. Warranty, certificates and product authenticity
10.1 What is the warranty on Grundfos pumps?
Grundfos provides a 24-month warranty on most products from the date of sale (not production). For registered customers via the myGrundfos portal, it is possible to extend the warranty on some products up to 5 years. Conditions for valid warranty include professional installation in accordance with technical instructions, use within permitted parameters, and availability of the purchase receipt. Warranty claims are handled through authorized dealers and service centers.
10.2 How can I recognize a counterfeit Grundfos pump?
Cheap imitations, mainly from Asian production, appear on the market, copying the visual design of UPS pumps. To verify authenticity: check the serial number on the type label at the Grundfos website (productfinder.grundfos.com), original products have specific weights and dimensions that imitations do not meet, and all original pumps for the European market have CE marking with a declaration of conformity. Always buy from authorized dealers – this will help you avoid not only fraud, but also warranty issues.
Frequently asked questions (FAQ)
Can I replace the UPS pump myself, without draining the entire system?
Yes, if you have shut-off ball valves on both sides of the pump (which is standard in proper installation). Close the valves, place a cloth under the pump, unscrew the nuts, and replace the pump. The whole process takes 20–40 minutes. If you don’t have valves, you will need to partially drain the system. Before replacement, turn off the boiler and wait until the heat transfer fluid cools to a safe temperature (under 40 °C).
What is the recommended operating pressure in the expansion tank for a system with a Grundfos pump?
The expansion tank pressure should be set to the system’s static pressure plus 0.2 bar. For a typical family house with a maximum pipe height of 7 m, the static pressure is about 0.7 bar, so the expansion tank is pre-charged to 0.9 bar. The total system operating pressure should not exceed 2 bar at maximum temperature. These values are not directly related to the pump, but incorrect settings can cause the pump to behave abnormally (e.g. knocking, pressure drops).
Is it possible to connect two Grundfos pumps into one system (series or parallel connection)?
A parallel connection of two identical pumps doubles the flow capacity at the same pressure – used in systems with high flow demand, for example in multifunctional buildings. A series connection doubles the pressure at the same flow – suitable for very high buildings. These connections are not used in family houses, but are standard in large new constructions or industrial applications. Grundfos has special mounting kits and documentation for such configurations.
Grundfos or Wilo – which brand is better?
Both brands are European leaders and their technical quality is comparable. Grundfos is a Danish manufacturer with a global network, Wilo is German. In practice, the specific model and its parameters for a given application decide, not the brand itself. On the Slovak market, Grundfos is slightly more widespread, which means better availability of spare parts and service technicians. If you buy a recommended model from a reliable seller, you will be satisfied with both brands.
How long does a Grundfos pump last without service?
Circulation pumps with wet rotor Grundfos UPS have a designed lifespan of 10–15 years without the need to replace components, provided the water quality in the system is good (neutral pH, no excessive hardness). Pumps for waste water, such as UNILIFT, should be inspected every 2 years – clean the intake, check the seals and electrical connections. Neglecting regular inspection can reduce lifespan by 30–50 %.
What to do if the pump makes loud noise or vibrations?
Noise can have several causes: cavitation (insufficient pressure at the inlet), air in the system, mechanical damage to the impeller, or improper mounting (the pump is not properly aligned, pipe tension strains the flange connection). The first step is always to bleed the system and check the pressure. If the noise persists, check whether the piping is too rigid – flexible hose connections can significantly reduce vibration transmission to the structure. Cavitation is characterized by a distinctive "crackling" sound and requires intervention in the system pressure or the pump position in the hydraulic circuit.
Conclusion
Grundfos pumps are technically advanced products with a long tradition and real engineering depth behind the model names. Choosing the right pump, correct installation, and minimal regular maintenance are the three pillars that determine whether your system will run smoothly for 15 years or cause you concern every winter. The range at atria.sk/grundfos/ covers all common applications – from water pumping through solar circuits to classic central heating – and for each product you will always find additional articles in this Knowledge Centre to help you make a decision.
Do you have a question on this topic?
Struggling to decide or dealing with a specific situation in your home? Write to us – we are happy to help.