Frequently asked questions about heating and water pumps
Common questions about heating and water pumps: a comprehensive guide
Over the years of working with heating technology, we keep coming across the same questions – from customers installing a pump for the first time, as well as from experienced installers who encounter an unusual case. This article collects the most practical, most frequent and most important questions that arise in connection with heating and water pumps, and answers them without unnecessary beating around the bush. You will also find technical explanations, numerical values and real-life examples from practical experience.
If you are looking for a more detailed introduction to certain topics, we recommend also reading other articles in this Knowledge Centre: How to choose the right pump for heating or water: step by step, Pump power and flow: how to calculate what you really need, or Circulating vs. pumping pumps: differences, advantages and when to use which. Here we focus precisely on questions that do not have enough space in those articles.
Basic questions about pump operation
How does the pump "know" how much water to pump?
This is one of the most common questions – and the answer depends on what type of pump it is. Older pumps with fixed speeds simply run at a constant performance and the water finds its own way through the path of least resistance. This means that if you have all the valves open on the radiators, the flow is maximum; when you close most of the valves (for example, thermostatic heads close at night), the flow decreases, but the pump still runs at the same performance – only the pressure increases and the flow decreases. The result is unnecessary energy consumption and sometimes noise as well.
Modern ECM pumps with electronically controlled motors and variable speeds solve this problem much more elegantly. They measure the differential pressure in the system and automatically adjust the speed to maintain a set pressure or flow value. When thermostatic heads close, the pump slows down – and saves energy. In practice, this means saving 50–80 % of electrical energy compared to an old fixed-speed pump, with the same or better comfort.
Why is hydraulic balance of the system important?
The pump itself will not solve a bad hydraulic design. If you have radiators in your house, some close to the boiler and others far away, without hydraulic balancing, the ones close will overheat and the ones far away will be cold – even if the pump is running properly. Hydraulic balance (balancing) means setting the flows in individual branches so that each radiator receives as much heat as it needs.
We see this problem very often in practice during the renovation of old houses, where the boiler and pump are replaced, but balancing is forgotten. The customer then thinks the pump is not working – but the problem is in the system setup, not the pump itself. We go into more detail on this in the article Installing a pump in a heating system: procedure and most common mistakes.
Questions about pump selection
What size pump do I need for a typical family home?
This is the question we get most often. And the answer is not simple, as it depends on several factors: boiler power, length of piping, number of radiators, their dimensions and type of piping system. Despite this, there are approximate values that work in practice for a typical family home:
- Family home up to 100 m² with boiler power of 10–15 kW: usually a pump with a flow of 1–1.5 m³/h and a head of 4–6 m is sufficient
- Home 100–200 m² with power of 15–25 kW: flow 1.5–2.5 m³/h, head 5–8 m
- Larger buildings or more complex systems with long piping: an individual calculation is needed
These values are only approximate. A correct calculation includes the hydraulic resistance of all pipes, fittings and heating elements. More about calculation can be found in the article Pump power and flow: how to calculate what you really need.
An important practical note: an oversized pump does not mean a better result. A pump with too high a performance causes increased noise (water noise in the pipes), unnecessary energy consumption, faster wear and in some cases even problems with regulation. It is always better to choose a pump "to measure" the system, or preferably one with variable speed, which can adjust itself.
What does a "three-speed" pump mean and when to choose it?
A three-speed pump (or multi-speed pump) has several fixed speed settings – for example, 1200, 1800 and 2400 rpm. The operator selects the speed manually or one is set permanently. Compared to single-speed pumps, this is an improvement, as you can at least roughly adapt the system – for example, use a low setting for underfloor heating in summer and a higher setting for full performance in winter.
Compared to modern ECM pumps with smooth regulation, however, they are still less efficient. For simple installations where there is no interest in investing in newer technology, or as a replacement pump in an old system, three-speed pumps are still a legitimate choice. In new installations, especially with condensing boilers or heat pumps, we would recommend an ECM pump today.
Can I connect a pump designed for heating also to drinking water or utility water?
No. This is a fundamental mistake that occurs mainly among people trying to save money by buying one "universal" pump. Heating pumps (circulating pumps) are designed for closed systems with antifreeze mixture or clean water, operate at temperatures of 2–110 °C and their materials (especially seals and internal parts) are not certified for contact with drinking water. On the contrary, pumps for drinking water must meet standards for food contact and hygiene – they use different materials and different seals.
In addition to hygiene risks, there is also a practical problem: a circulating pump is designed to work in a closed circuit with minimal pressure – it cannot suck water from a well or a tank. For this purpose, completely different types of pumps are used (self-priming pumps, submersible pumps, etc.).
Questions about installation
Flow direction and pump orientation – what to pay attention to?
The circulation pump has a clearly defined flow direction of the medium – it is always marked with an arrow on the body. This arrow must match the actual flow direction of water in the pipe; otherwise, the pump will work in the opposite direction, which can cause significantly reduced flow and increased noise.
Regarding spatial orientation: most modern circulation pumps can be installed in a horizontal or vertical position (with the motor up, to the side, but not with the motor down – the shaft would be stressed differently and the oil in the bearings would not lubricate properly). Always read the instructions for the specific pump – some types have limitations on orientation. Neglecting this rule risks premature bearing wear.
In practice, we have seen cases where the installer forgot to check the arrow direction and the pump was connected "backwards". The boiler was heating up, but the radiators remained cold – and the customer was convinced the pump was broken. After reversing the pump, the problem was immediately resolved.
Should a filter (sludge separator / magnetic filter) be installed before the pump?
Definitely yes, for several reasons. Boiler water in older systems contains various impurities – sludge, rust, oxides, and sometimes even small fragments of old pipe or gasket. These impurities damage the pump impeller blades, clog sealing surfaces, and shorten the pump's lifespan. A magnetic filter also captures magnetic metal particles (e.g., rust from steel radiators), which a standard mesh filter cannot catch.
The filter is installed before the pump inlet (on the suction port, or before the pump according to the flow direction). The choice of mesh fineness depends on the system – commonly used is 0.5 mm for circulation pumps. It is important to clean the filter regularly, otherwise it itself causes a drop in flow.
Is it necessary to bleed the pump before the first start?
Yes, and this operation must not be neglected. Air in the pump causes the impeller to "run dry" – it does not find the medium to push, and the motor can overheat. Most modern circulation pumps have a bleed screw (usually on the side or top of the motor part). Procedure:
- Fill the system with water and briefly turn on the pump (5–10 seconds)
- Turn off the pump and slowly loosen the bleed screw – air will escape
- Tighten the screw again (not too tightly – it is plastic or brass)
- Repeat the process 2–3 times until only clean water without bubbles flows out of the opening
- Check that the pump makes an even, quiet sound (without sputtering or rumbling)
A more detailed installation and start-up procedure can be found in the article Mounting a pump in a heating system: procedure and most common errors.
Questions about operation and energy consumption
How much electrical energy does a circulation pump consume?
This depends on the type of pump and its setting. Old pumps with fixed speeds (e.g., series "25-40", "25-60", etc.) have a power consumption of 40–100 W and run continuously throughout the heating season. Calculation: 100 W × 24 hours × 180 days (6 months) = 432 kWh per year. At a cost of 0.25 €/kWh, this is about 108 € per year just for the pump.
Modern ECM pumps operate at 5–20 W under normal load. Even if we calculate an average consumption of 15 W × 24 h × 180 days = 64.8 kWh per year = about 16 € per year. The savings are therefore realistically 80–90 € per year – this means the price difference in purchase (usually 30–80 € more for an ECM pump) is paid back in 1–2 years.
In the long term – with a pump lifespan of 10–15 years – the energy savings amount to 800–1350 €. This is a very strong argument for ECM pumps, even if the customer is not primarily interested in ecology, but in the economics of operation.
Should the pump run continuously or only when heating?
This depends on the system and the regulator setting. In systems with a boiler and thermostat, it is standard for the pump to run whenever the boiler is firing (or shortly before and after firing). When the thermostat reaches the desired temperature and the boiler turns off, the pump should also stop – running it continuously without the boiler makes no sense and increases consumption.
Modern boilers have a pump output that controls the pump automatically. If the pump runs continuously even when the boiler is not doing anything, the problem is either in the regulator setting or in a wiring issue. In the case of a heat pump or floor heating, continuous pump operation may be intentional – to prevent sedimentation and maintain an even temperature profile in the floor.
What pressure should be in a closed heating system?
The static pressure in a cold state should typically be 1–1.5 bar for a single-story family house and 1.5–2 bar for a two-story house. The pressure must not drop below 0.5 bar (risk of cavitation and air in the system) or rise above 2.5–3 bar (depends on the expansion tank and safety valve). When the system is heated, the pressure naturally rises by 0.3–0.8 bar – this is a normal phenomenon.
If the pressure continuously drops, water is leaking somewhere (system failure). If it rises above the allowed value, the expansion tank (membrane pre-pressure) or safety valve should be checked. More about these parameters can be found in the article Pressure and head: what do these parameters mean and why are they important.
Questions about faults and repairs
Pump is buzzing or vibrating – is it a problem?
Mild buzzing is normal – it is the sound of the motor and flowing water. A problem occurs when the noise suddenly changes or when the noise is significantly higher than usual. The most common causes of increased noise:
- Air in the system: causes gurgling, bubbling and irregular sound – solution: bleeding
- Clogged impeller: sludge or dirt causes uneven operation – solution: cleaning or replacing the impeller
- Too high speed: the pump is running at a higher stage than necessary – solution: reducing the speed
- Worn bearings: characteristic grinding or metallic sound – solution: replacing the pump
- Inappropriate installation: vibrations are transferred to the pipe (without dampers) – solution: installation of flexible couplings
Detailed solutions for each case can be found in the articles Pump noise: why it buzzes or vibrates and how to eliminate it and Common heating and water pump failures: causes and solutions.
Pump is rotating, but water is not flowing – what is wrong?
This is one of the most common service cases. The pump makes a sound, the motor is rotating, but the flow is zero or minimal. Possible causes:
- Blocked impeller (sludge, deposits) – the most common cause after a long period out of operation, for example in spring during the first start-up
- Air in the pump – the impeller is pumping air, not water
- Closed shut-off valves before or after the pump
- Clogged filter before the pump
- Motor failure (winding) – the motor does not seem to be broken, but is not rotating strongly enough
First step: check whether all shut-off valves are open. Second step: bleed the pump. Third step: check and clean the filter. If nothing helps, try to unblock the impeller – on most pumps it is possible through the bleed valve: insert a thin screwdriver and gently turn the shaft.
Questions about maintenance and lifespan
How long does a circulation pump last?
With proper installation, clean water in the system and regular (at least once a year) inspection, a modern circulation pump can last 15–20 years. Older types with permanent lubrication and simpler construction could last 25 years, but on the other hand they consumed much more electricity.
Factors that shorten lifespan: hard water with high calcium content (creates deposits on the impeller and in seals), dirty water with sediments, inappropriate installation orientation, too high or too low pressure in the system, and long-term operation with air in the circuit.
Factors that prolong lifespan: magnetic filter, water pH adjustment (ideally 7.5–9 for heating systems), regular bleeding, annual visual inspection of seals and connections, and proper pump sizing (the pump must not be constantly overloaded).
Is pump maintenance required and how?
Modern sealed circulation pumps are essentially maintenance-free – they do not have a mechanical seal with lubricant, the shaft floats in the medium itself (water). Despite this, we recommend at least once a year (at the beginning of the heating season):
- Check whether the pump starts and runs properly
- Visually check the seals and connections – no moisture or drops
- Clean the filter before the pump
- Check the pressure in the system and add water if necessary
- For ECM pumps, check the settings – correct regulation curve
More about maintenance can be found in the article Pump maintenance and service: how to extend lifespan and avoid failures.
Special situations and less common questions
Can I use one pump for heating and for hot domestic water (HDW)?
It is not recommended and is not done in practice. The heating circuit and the HDW circuit are separated – either through a heat exchanger or through the HDW tank. Each circuit has its own pump with its own settings. Reason: the heating circuit operates at different temperatures and pressures, different operating times and intensity than the circulation circuit for HDW. The HDW circulation pump is also specified for work with potable water.
If your system has an HDW tank with circulation, you need a separate small circulation pump for HDW (usually very low power, 5–20 W) and a separate circulation pump for the heating circuit. These two circuits do not exclude each other – they usually operate in parallel.
What to do if the pump freezes?
Pumps in well-designed heating systems indoors normally do not freeze. Problems occur with pumps in floor or semi-outdoor piping, in systems in recreational buildings (cottages, chalets) or in pumps in technical rooms without sufficient heating.
Prevention: add an antifreeze mixture (propylene glycol mixture, for home heating usually 30–40 % concentration protects down to -15 to -20 °C) to the system. Alternatively, when the building is out of use, drain the system. Never drain the system with antifreeze into the sewer without the appropriate permit – it is environmentally and legally problematic.
If the pump has frozen: do not try to force it to rotate. Let the system thaw slowly at room temperature. After thawing, check the seals and the entire system for possible cracks and leaks. Frost can damage not only the pump, but also the piping.
Why is the pump working, but the radiators are not heating evenly?
The pump is doing its job – it is pushing the medium through the system. Uneven heating of radiators is a hydraulic problem, not a pump problem. Typical causes:
- Unbalanced hydraulics – nearby radiators have too much flow, distant ones too little
- Clogged thermostatic heads – they do not open fully
- Clogged specific radiator – deposits inside
- Insufficient boiler power for the size of the heated area
- Air in some radiators – bleeding is needed
Solution: hydraulic balancing of the system (setting balancing valves on each branch), bleeding all radiators, checking thermostatic heads and flushing clogged radiators.
Most Frequently Asked Questions (FAQ)
Can I replace the pump myself, or do I need a professional?
Replacing a circulation pump is a relatively simple task that a skilled DIY enthusiast can manage. You need to know how to close the relevant valves, partially drain the system, replace the pump, and refill and bleed the system again. Problems may arise if the valves are seized (cannot be closed), or if the system does not have proper shut-off valves near the pump – in that case, you will need to drain the entire system. In any case, if you are unsure, it is wise to call a plumber. A poor connection or a loose pipe can cause damage exceeding several times the cost of the pump. A step-by-step procedure is available in the article Pumps in heating system renovation: Replacing an old pump step by step.
What is the difference between a "25-40" and a "25-60" pump?
These designations are a standardized format: the first number is the pipe connection diameter in mm (25 mm = 1"), the second number is the maximum head in dm (40 dm = 4 m, 60 dm = 6 m). A 25-60 pump can therefore create a head of up to 6 m, which is more suitable for larger or more extensive systems. A 25-40 or 25-60 is usually sufficient for a small family house, while a 25-60 or even a 32-60 is suitable for a larger house or long pipe runs. Note – these numerical designations apply to older types; modern ECM pumps are labeled differently and their hydraulic parameters are set electronically.
Can I leave the pump unused all summer long?
Yes, but with one precaution: it is common at the beginning of the heating season that a pump that has been stationary all summer has a blocked (locked) impeller. Dirt and deposits can stick to it. Therefore, we recommend running the pump for 5–10 minutes at least once a month (even in summer) to keep the impeller moving and prevent it from sticking. Some modern pumps have a built-in "summer mode" – they automatically start briefly at regular intervals precisely to prevent this issue.
What is cavitation and how can I recognize it?
Cavitation is a physical phenomenon in which vapor bubbles (not air bubbles) form in the pump as a result of local pressure dropping below the vapor pressure of the liquid. The bubbles form and immediately implode, creating a characteristic noise similar to gravel being poured into the pump. Prolonged cavitation causes significant erosion of the impeller and the pump body. Causes: too low inlet pressure, too high medium temperature, clogged suction filter, or the pump is operating outside its working range. The solution includes checking and increasing the inlet pressure, reducing the medium temperature at the inlet, or re-evaluating the pump sizing.
Is it better to have one strong pump or several smaller ones?
For larger or more complex systems (multi-story houses, systems with multiple zones, public buildings), the correct answer is several smaller pumps – one for each zone. This approach allows for more precise regulation of each zone, easier maintenance (replacing one pump does not shut down the entire system), and higher overall efficiency. For a standard family house with one heating zone, a single properly sized pump is the optimal solution.
Can I connect a new ECM pump to an old boiler (non-condensing)?
In most cases, yes. An ECM pump is hydraulically compatible with standard connections (1" or 6/4") and works in any closed heating system. The only exception may be the electrical connection: some older boilers have a control contact for the pump that may not be compatible with an ECM pump (e.g., 0–10V control signal). Always check the boiler documentation. If the boiler does not have special control, the ECM pump can be simply connected directly to the grid (230 V) and manually set to the appropriate control curve. Result: significant energy savings even in an old system.
Conclusion: A practical overview of what to remember
Pumps are the heart of every heating or water system – but like any heart, they function properly only when the entire circulation system is correctly designed. From decades of experience in practical work, we know that most pump problems are not related to the pump itself, but to its sizing, installation, hydraulic balancing of the system, or the water quality in the system.
An investment in a modern ECM pump pays for itself within 1–2 years through electricity savings. A filter before the pump is not an optional accessory, but a necessity. Bleeding the system after each installation and at the beginning of each season is a quick task that prevents most service calls. And if the pump makes unusual noises – do not ignore it, it is usually the first sign of a larger problem.
If you have a specific situation that we have not covered here, check out other articles in this Knowledge Center – for example, Common pump failures for heating and water: causes and solutions for specific service scenarios, or How to choose the right pump for heating or water: step by step if you are just starting out and need an overall overview before making a choice.
Do you have a question about this topic?
Are you unsure or dealing with a specific situation in your home? Write to us – we are happy to help.