Frequently Asked Questions about Circulation Pumps
Common Questions About Circulation Pumps – Answers You’ve Been Looking For
The circulation pump is the heart of every hydronic heating system. Despite this, most people don’t deal with its selection, installation, or adjustment until something stops working – or until they are preparing for a renovation. In this article, we have gathered real questions our customers ask us every day and answered them the way we would explain them directly in the store: without cutting corners, with specific numbers, and with real-life examples.
If you are looking for more specific topics – for example, how to calculate performance, how wet-rotor and dry-rotor pumps differ, or how to properly set the speed – we have separate articles on these topics in our Knowledge Center. Here, we focus on what most people ask: basic doubts, common mistakes, and practical decisions.
1. What is the purpose of a circulation pump and can I heat without it?
A circulation pump ensures a continuous flow of hot water between the boiler (or another heat source) and the heating elements – radiators, floor heating, or fan coils. Without a pump, water would move only by natural convection, which was actually used in old gravity-based systems.
Gravity circulation works, but it has fundamental limitations. It requires very thick pipes (diameters 50–80 mm), the house must have the boiler in a significantly lower position than the radiators, the system reacts more slowly, and heat losses through the pipes are greater. In a modern house with a condensing boiler, floor heating, or a heat pump, gravity circulation is practically impossible – pressure losses are too high and water temperatures are too low.
So: yes, theoretically you can heat without a circulation pump, but only in a specifically designed gravity system. In 99% of new and renovated homes, a pump is a necessity.
2. What are the differences between various types of circulation pumps?
This question confuses many people because manufacturers use different names. The basic classification is as follows:
Wet-rotor vs. dry-rotor
A wet-rotor pump has the rotor submerged directly in the transported liquid – the water also lubricates the bearings. They are quiet, do not require any bearing maintenance, and are significantly more common in residential homes. A dry-rotor pump has the motor separated from the hydraulic part, the bearings are air-cooled and greased. They are noisier, larger, but can transfer much higher outputs – you typically find them in apartment buildings, industrial facilities, or large commercial buildings.
For a single heating circuit in a family home, a wet-rotor pump is always the right choice. A more detailed comparison can be found in the article Difference Between Wet-Rotor and Dry-Rotor Circulation Pumps.
Pumps with fixed speed vs. electronically controlled (EC motor)
Older pumps had fixed speeds or a 3-speed switch. Modern pumps with EC (electronically commutated) motors and integrated electronics automatically adapt to the current system needs. Energy savings compared to old fixed-speed models can be 50–80%. Pumps of energy efficiency class EEI ≤ 0.23 are now the standard in the EU and have been mandatory since 2015. An old pump with a power consumption of 80–120 W can be replaced with a modern one that consumes 5–25 W in normal operation.
In-line pumps
A special category is in-line (on-pipe) pumps of larger dimensions, where the flange on the inlet and outlet is in one axis. These are used in industrial applications, large radiator circuits, or in solar systems with larger pipe diameters.
3. How do I know that my old pump needs to be replaced?
From experience, we know that customers come for a replacement either too late (the pump has jammed in the middle of winter) or too early (the pump is still working, but just sounds different than before). Here are the specific symptoms that indicate it:
- Noise: New buzzing, knocking, or whining from the pump – it may be air in the system, worn bearings, or cavitation. Air can be bled out, but worn bearings cannot.
- Certain radiators are cold: If the pump cannot push water through all circuits, distant or higher-positioned radiators remain cold. This usually means the pump has insufficient power or is clogged with scale.
- Excessive energy consumption: If the pump draws the same power as it did 20 years ago (80–150 W), it is a clear reason to replace it with a modern model (5–25 W). The economic payback is usually 2–4 years.
- The pump does not start: The most common cause: the rotor is blocked by scale deposits. In many cases, bleeding air and loosening the rotor with a screwdriver helps (details can be found in the article Common circulation pump faults and their solutions).
- Age over 15 years: An old pump that still works does not necessarily mean it works well. If it is old and non-adjustable, replacing it with a modern model is economically justified.
4. How do I know if my pump has sufficient capacity?
The performance of a circulation pump is characterized by two values: flow rate (l/h or m³/h) and head (m w.c. – meters of water column). In order to determine whether the pump is correctly dimensioned, we need to know the thermal output of the system and the pressure losses in the piping.
Simplified flow rate calculation: with a temperature difference of 20 °C between the supply and return, you need a flow rate of approximately 43 l/h for every 1 kW of thermal output. Therefore, a house with a 15 kW boiler requires a flow rate of at least 15 × 43 = 645 l/h ≈ 0.65 m³/h. The head depends on the length and diameter of the pipe – typically 1–4 m w.c. for a family house.
If you are unsure about the calculation, you can read a separate article What circulation pump capacity do I need for my house?, where the process is explained step by step, including tables for different types of houses.
Practical tip from practice: most manufacturers (Grundfos, Wilo, DAB) offer online selectors or mobile apps where you enter the system parameters and they recommend a specific model. This is more reliable than estimating.
5. Can I replace the pump myself, or do I need a professional?
It depends on the situation. If you are replacing the pump with the same size (same construction length, same connection threads), it is a relatively simple task that a skilled DIY person can handle. You will need: wrenches, a container for water, a new gasket, Teflon or hemp fiber for the threads.
If you are replacing the pump on a condensing boiler, heat pump, or if you plan to add a hydraulic balancer, zone control or automation at the same time – we recommend a professional. Not because you cannot do it, but because incorrect installation (e.g. reverse flow direction, incorrect rotor position, missing air venting) can lead to problems that only become apparent after years.
Legal aspect: in Slovakia, there is no law stating that pump replacement must be performed by a certified person (unlike gas appliances). However, some boiler warranties may require professional installation. Check the warranty conditions of your boiler before you reach for the wrench yourself.
A step-by-step installation procedure can be found in the article Installation of a Circulation Pump Step by Step in the Knowledge Center.
6. In what position is the circulation pump installed?
This is a question where surprisingly many mistakes are made. A wet-rotor pump can be mounted in several positions, but not in all. Basic rules:
- The rotor axis must be horizontal – this is the most important rule. If it were vertical (pump "standing"), an air bubble could get trapped at the bearing and cause overheating and rapid wear.
- The electrical terminal box (terminal block) must point upwards or sideways – never downwards. Condensation or possible leakage could flood the electronics.
- Flow direction is indicated by an arrow on the pump body. Before installation, make sure the direction matches the design.
7. Where exactly in the system is the circulation pump installed?
The classic placement is on the return pipe before the boiler – that is, the pump "sucks" the cooled water from the return and pushes it into the boiler. The reason is simple: the temperature is lower on the return, which prolongs the pump's lifespan and reduces the risk of water evaporation at the mechanical sealing surface.
In modern systems with condensing boilers, the pump is often integrated directly into the boiler. If the boiler already has a pump and you are adding another circuit (e.g., floor heating or a water heater), you need an additional pump for this circuit – usually after the mixing valve or hydraulic balancer.
Special rules apply to solar systems and heat pumps – more on this in the article Circulation pump for a heat pump or solar system.
8. How do I set up the circulation pump after installation?
Modern electronic pumps usually have these modes:
- Fixed speed (I/II/III): The pump runs at a constant speed. Suitable for simple systems where you need a precisely defined flow and do not want the pump to adapt.
- Proportional pressure (ΔpV): The pump maintains pressure proportional to the flow. When thermostatic valves close (reducing demand), the pump reduces its performance. Recommended mode for most radiator systems.
- Constant pressure (ΔpC): The pump maintains the same pressure regardless of the flow. Suitable for systems with long pipe runs or floor heating with less regulation.
- AutoAdapt / Auto: An intelligent algorithm that automatically finds the optimal point. Some premium models such as Grundfos ALPHA, Wilo Yonos, or DAB Evosta have this mode.
We describe the correct mode selection and setup in detail in the article Setting the speed and performance of a circulation pump.
9. What do the numbers in the pump name mean (e.g., 25-60, 32-80)?
This is a very practical question. The two numbers in the pump name (separated by a hyphen) always have the same meaning:
- First number = pipe thread diameter in mm (25 = DN25 = 1", 32 = DN32 = 1¼")
- Second number = maximum head in dm (i.e., 60 = 6.0 m w.c., 80 = 8.0 m w.c.)
Example: Grundfos ALPHA2 25-60 has 1" (DN25) pipe threads and a maximum head of 6 m. The third parameter you often see in the name is the construction length – e.g., 130, 180 or 130 mm. This is the distance between the centers of the pipe threads and must match what you have in your piping.
The most common construction lengths for family homes are 130 mm (compact boilers) and 180 mm (older standard). Always measure this number before purchase!
10. Why does the pump hum or make noise?
Noise is one of the most common reasons customers contact support. There are several causes, and each sounds different:
- Buzzing / vibrations: Most often air in the system. Try bleeding the radiators and the pump itself (bleed screw on the front of the pump). Reducing the speed also helps.
- Loud humming at max performance: The pump is oversized or set to unnecessarily high speed. Try reducing the speed to a lower level or switching to the proportional pressure mode.
- Clicking / rattling: Damaged rotor or foreign objects in the hydraulic part. This is a serious symptom – the pump needs to be replaced.
- Water noise (flowing, "gurgling"): Too high differential pressure with closed thermostatic valves. Solution: reduce the set differential pressure or add a differential bypass valve.
- Cavitation (crackling noise): Occurs when the pressure at the pump inlet drops below the boiling point. Causes: too long or narrow suction pipe, clogged filter, or expansion tank with insufficient pre-charge pressure.
11. How much electricity does a circulation pump consume?
This surprises customers when we show the difference between old and new technology. A comparison from real cases:
- Old pump Grundfos UPS 25-60 (3-speed, common type until 2013): power consumption 50–85 W, in operation all year = 440–745 kWh/year = approx. 90–150 € per year at 0.20 €/kWh
- Modern pump Grundfos ALPHA3 25-60: typical power consumption 3–25 W, average ~8 W = 70 kWh/year = approx. 14 € per year
The difference is dramatic – a saving of over 100 € per year just for one pump. Investment in a modern pump (price 80–160 €) pays back in 1–2 heating seasons. So if you have a pump older than 10 years in your house and it is still working "normally" – consider replacing it anyway.
12. Do I have to drain the entire system when replacing the pump?
Not necessarily – it depends on whether you have (or can install) shut-off valves directly at the pump. Many older installations do not have them, in which case you have to drain at least the part of the system where the pump is located.
In practice, it looks like this: close the supply and return of the pump (if there are valves), prepare a container and hose under the pump, loosen the bleed screw on the pump and let the remaining water drain out. With good preparation, you can replace the pump in 30–45 minutes without draining the entire system.
Important: always bleed the entire system after a new installation and check or top up the pressure (typically 1.5–2.0 bar when cold). After starting up, check the tightness of all connections.
13. What are the differences between Grundfos, Wilo and DAB?
This is a question for a separate article – and we have it: Comparison of circulation pumps Grundfos, Wilo and DAB. In short: all three brands produce high-quality, reliable products with similar parameters in their respective price segments. Grundfos (Danish) is a long-term global leader and has the most extensive service network; Wilo (German) is strong in technical innovations and premium models; DAB (Italian) offers excellent performance-to-price ratio and is popular in smaller homes during renovations.
In a typical family home without extreme requirements, the difference in daily operation is minimal. More depends on correct sizing than on the brand.
14. What is hydraulic balancing and is it related to the pump?
Yes, directly. Hydraulic balancing of the system means that each radiator receives exactly as much water as it needs – no more, no less. If the system is not balanced, radiators near the boiler are overheated and distant ones are cold, the pump has to overcome unnecessarily high pressure losses and operates inefficiently.
Hydraulic balancing is done by setting the preset values on thermostatic valves. Without this setting, you can have the best pump on the market and the system will still work poorly. It goes hand in hand with pump selection – which is why we mention it in the article How to choose a circulation pump for central heating.
15. Can I use one pump for multiple circuits?
It depends on the configuration. If you have a single one-circuit system (boiler → radiators → return), one pump is sufficient. If you have a multi-circuit system (e.g. radiators + floor heating + water heater), each circuit usually needs its own pump, or a hydraulic equalizer (low loss header) with a separate pump for each circuit.
A solution with one pump for two circuits of different temperatures (e.g. radiators at 70 °C and floor at 35 °C) does not work technically without a mixing valve and a separate pump for the floor circuit. Attempts to save money here lead to overdimensioning of one circuit and underdimensioning of the other.
16. How long does a circulation pump last?
Modern wet-rotor pumps are designed for operation for 15–25 years, provided the system is properly filled, degassed and the water has appropriate quality (pH 7–9, low hardness). In practice, we see pumps that work for 25 years without problems – but also those that need to be replaced after 8 years because the system was filled with aggressive water or the pump was operated in an incorrect mode.
Factors that shorten the lifespan:
- High water hardness (limescale on the rotor and bearings)
- Air in the system (corrosion, cavitation)
- Too low or too high pressure in the system
- Operation "dry" due to a failure of the expansion tank
- Vibrations from the surroundings (pump located directly on masonry next to a circulation pump)
For more information on how to take care of the pump to make it last as long as possible, see the article Maintenance and service of a circulation pump.
Most frequently asked questions (FAQ)
Can I leave the circulation pump running in summer?
It depends on the system. If you have solar heating or a heat pump for hot water preparation, the pump must run year-round. If you use the pump only for central heating with a conventional boiler, you can safely turn it off in summer – you will save energy. Some modern boilers have a function for regular short-term pump activation in summer (rotor lock), which is an excellent feature – it prevents the rotor from seizing after a long break.
Why do I have air in the radiators even after bleeding?
If air keeps appearing in the system (you bleed it out, and after a month it is there again), the problem is not in the bleeding, but in its cause. Most common reasons: low pressure in the system (expansion tank has insufficient pre-pressure or is damaged), micro-leakages in the system, or corrosion processes (corrosion of metal parts generates hydrogen). In such cases, you need to address the cause, not just the symptom.
How much does it cost to replace a circulation pump including labor?
The price of the pump itself for a family house ranges from about 60 € (basic models) to 200 € (premium EC models). Labor for an installer for a simple replacement (same size, accessible location) is typically 1–2 hours, i.e. 60–150 €. Overall, expect to pay 120–350 € including materials and labor. Replacing an old energy-intensive model with a modern one pays for itself in 1–3 seasons.
What does it mean if the pump is running, but the house is not heating up?
If the pump is running mechanically, but heating is not working, the problem may be: (1) the pump is running "dry" – there is no water in the system, (2) the flow direction is reversed – the rotor was removed and installed backwards, (3) the pump is significantly underdimensioned and cannot overcome the system's pressure losses, (4) clogged filters or thermostatic valves are fully closed. Start by checking the pressure in the system on the boiler's pressure gauge.
Is it true that the pump needs to be "started up" occasionally in summer?
Yes, it is good practice. A rotor in stagnant water can "stick" due to limescale deposits after the summer season. Modern boilers solve this problem automatically – they have a "pump kick" (anti-blocking) function that runs the pump briefly every few days even without a heating demand. If your boiler does not have this function, manually start the pump once a month.
Can I install a larger pump than recommended by the project, "just to be safe"?
No, this is a mistake we see regularly. An overdimensioned pump does not improve heating performance – it brings noise (flowing, whistling thermostats), increased energy consumption, wear on thermostatic valves, and system instability. Always dimension the pump according to the actual system parameters. Modern EC pumps also automatically reduce performance when demand is low, so a slight reserve in dimensioning (10–20 %) is acceptable, but not 50–100 %.
Conclusion: A circulation pump is not just a "minor detail"
After reading this article, we hope it is clear: a circulation pump is just as important a part of the heating system as the boiler or radiators. The correct selection, proper installation, and correct setting directly affect how much you pay for energy, how quietly your system operates, and how long it lasts without problems.
If you are still looking for a specific model, visit our category circulation pumps, where you will find the current range of available products. If you need help with selection, first check the related articles in the Knowledge Center – whether it is about performance calculation, brand comparison, or a specific installation procedure. You can solve most questions before you even pick up the phone.
Do you have a question about this topic?
Can't decide or are you dealing with a specific situation in your home? Write to us – we are happy to help.