In most homes, the circulation pump is set once, during installation, and then no one touches it for years. Meanwhile, the pump setting is responsible for some of the problems installers encounter most often: noise in the pipes, surprisingly high heating bills, and uneven heating in different rooms. In this article, we explain what the symbols on the pump mean, which mode suits which system, and why settings used for decades work against you in a modern pump.
The subject of circulation pump modes has already been covered on our website. The article on Controlling the operation of circulation pumps explains the benefits of electronic control of the device's operation. Today's article not only updates the information provided earlier, but also answers questions about the markings found on these pumps. If you want to learn more about proportional pressure, constant pressure, or AUTO mode, read it to the end.
Three symptoms that usually indicate an incorrect setting
Before we move on to the theory, it is worth checking whether the problem affects you at all. In our experience, an incorrect circulation pump setting most often manifests itself in three ways.
- Humming, hissing, or buzzing in the system. This is most often audible at night, when the house is quiet, and intensifies when the thermostatic radiator valves start closing. This is a classic symptom of a pump forcing more water through the system than it can accept.
- High power consumption during continuous operation. The circulation pump operates throughout the heating season, several thousand hours a year. A difference of several dozen watts between settings adds up to hundreds of kilowatt-hours over the course of a year.
- Uneven heating. Radiators closest to the boiler are hot, while the ones farthest away are barely warm. The pump setting can be one of the causes, but not the only one, and we discuss this further below.
If you recognize any of these symptoms, we start with the simplest thing you can do without tools: checking which mode your pump is operating in.
The highest-speed myth, or where half the problems come from
On the internet and in conversations with installers, one piece of advice keeps coming up: set the pump to its highest speed and it will heat better. This advice did not come from nowhere and once made sense. With older three-speed pumps, adjusted manually, the operating point was determined so that the system would function properly at the highest available speed.
The problem is that a modern electronic pump is built around exactly the opposite principle. Its purpose is to reduce its output when the system needs less water and increase it when more is needed. Setting it permanently to the highest constant speed disables all this logic. The pump stops responding to the system, runs at maximum all the time, and produces exactly the symptoms mentioned above: noise, excessive power consumption, and a flow rate that the system cannot handle.
So if you have a pump with a display and a mode-selection button, and it is set to the highest constant speed, you are most likely paying for a feature you are not using.
What the symbols on a circulation pump mean
Mode designations can be confusing because manufacturers use different abbreviations for the same physical phenomena. In our pumps, for example in the BETA 2 series and the IVO series, the configuration is also used by many other electronic devices on the market. Both series offer eight operating modes.
- ECO or an automatic-mode designation: the factory setting in which the pump automatically selects the characteristics to suit the system.
- PP followed by a number, such as PP1 and PP2: proportional-pressure curves.
- CP followed by a number, such as CP1 and CP2: constant-pressure curves.
- I, II, III: constant-speed curves, equivalent to the old speed settings.
The number next to PP and CP indicates the curve level, meaning how hard the pump operates in a given mode. A lower number means a lower curve and lower energy consumption.
Proportional pressure (PP)
In this mode, the pump reduces the head as the flow rate decreases. When the thermostatic valves at the radiators begin to close because the rooms are getting warmer, the pump detects this and slows down. The effect is twofold: power consumption decreases and the noise caused by water forcing its way through heavily throttled valves disappears.
This is the most energy-efficient of the controlled modes and the natural choice wherever the system regulates itself, meaning in a typical radiator system with thermostatic heads.
Constant pressure (CP)
Here, the pump maintains the set head regardless of how much water is currently flowing through the system. It is less efficient than proportional mode, but more resistant to unusual system behavior.
It works well in systems with low resistance and large pipe diameters, especially underfloor heating, where the circuits require stable available pressure. It is also a safe choice when modernizing an older system for which we do not have design documentation.
Constant speed (I, II, III)
The pump operates at the same rotational speed all the time and does not respond to what is happening in the installation. It behaves exactly like an old three-speed pump.
This is not a bad mode in itself, but a mode for specific applications: simple systems without regulation, gravity-fed installations converted to pump operation, domestic hot-water circulation circuits, and those parts of systems that require a guaranteed, constant flow. The problem only begins when it is set in a modern installation with thermostats, where it wastes the pump's capabilities.
Which mode for which installation
The practical rule can be reduced to a few cases. Treat it as a starting point, not a strict requirement, because the final choice depends on the specific installation.
- Radiators with thermostatic valves, two-pipe system: proportional-pressure mode (PP), because the installation regulates the demand for flow itself.
- Underfloor heating: constant-pressure mode (CP) - the circuits need stable operating conditions.
- A single-pipe, series installation: a lower proportional curve, such as PP1.
- An unregulated, gravity-fed installation converted to pump operation: constant speed or a low constant-pressure curve.
- You are not sure what type of installation it is: leave the factory setting, that is, automatic mode. In our pumps, this is ECO, and for most typical domestic installations it is the right choice.
The last point is more important than it may seem. If someone changed the factory setting without a specific reason, the best move is often simply to return to automatic mode and monitor the installation for a few days.
How much you can realistically save
Here, you need to distinguish between two completely different figures, because they are regularly mixed up in industry materials.
The first concerns replacing an old non-regulated pump with a modern electronic one. Here, the differences are genuinely large, because electronic pumps consume between one-tenth and one-third of the electricity used by conventional designs. For comparison: our older OHI 25/60 three-speed pump consumes 46 W in first gear, 67 W in second gear, and 93 W in third gear. Modern designs, such as the IVO series, range from 5 to 60 W depending on the load, with an energy efficiency index (EEI) no higher than 0.23.
The second figure concerns only changing the mode of the pump you already have, and is much more modest. Independent scientific publications analyzing variable-speed and pressure-controlled pumps indicate savings of around thirty to fifty percent compared with operation at a constant speed. That is still a great deal for a change that takes a few seconds and costs nothing, but it is not the same value as replacing the device.
Even among three-speed pumps, the difference can be significant. In the model mentioned above, switching from the highest speed to the first reduces power consumption by almost half. With several thousand hours of operation during the heating season, that means real savings, not a statistical trifle.
On our website, you will find an energy savings calculator that will help you estimate how much replacing your old circulation pump could save you.
How to choose the setting for your system
We do not provide a ready-made step-by-step guide because the menu layout and setting ranges vary between models, and each pump should be set according to its operating manual. Instead, we provide a method that works regardless of the device.
Start with the mode appropriate for your installation type, based on the list of suggestions above. Then monitor two things for several days, preferably in colder weather when the installation is operating under load. The first is thermal comfort in the rooms furthest from the boiler. The second is noise in the installation, especially in the evening and at night.
If you hear noise, go down one curve. If the most distant radiators are not heating sufficiently, increase the setting by one level. A setting that is too high means noise and unnecessary power consumption, while one that is too low means rooms at the end of the circuit will not be heated sufficiently. The correct setting is the lowest value at which the entire installation heats properly.
When an incorrect setting is not the whole problem
It is worth being aware of the limits of this method. The pump setting determines how much water circulates throughout the installation, but not how that water is distributed among individual radiators. If, after trying all the modes, some rooms are still noticeably warmer than others, the cause lies elsewhere, and increasing the pump setting will not solve it - it will only add noise.
The same applies to an air-locked or contaminated installation. Sediment and air in the system can cause symptoms very similar to an incorrect setting, and no change of mode will remove them. In such situations, the next step is to check the condition of the installation itself, rather than continue experimenting with the pump.
If your current pump does not have electronic modes and only has a speed switch, it is worth considering replacing it. In our range, you will find circulation pumps and installation accessories, as well as a separate category featuring energy-efficient circulation pumps with electronic control and an A rating. We explain more about how such solutions affect operating costs in our article about energy-efficient circulation pumps for central heating systems.
Dambat - a trusted manufacturer of pumps and hydrotechnical equipment with quality certificates.
Frequently asked questions
At what speed should the circulation pump operate?
In a modern electronic pump, it generally should not operate at a constant speed at all, but in a regulated mode: proportional pressure for a radiator system with thermostats, or constant pressure for underfloor heating. Constant speeds I, II and III are intended for systems without regulation.
Will setting the pump to the highest speed make the house heat up faster?
No. A higher setting increases the water flow in the system, but if the system cannot accept that amount of water, the excess results in noise and higher electricity consumption, not additional heat. With an electronic pump, the highest constant speed also disables automatic regulation, which is the device's main advantage.
What do the PP and CP symbols on a circulation pump mean?
PP refers to proportional-pressure curves, in which the pump slows down as the flow decreases. CP refers to constant-pressure curves, in which the pump maintains the set head regardless of the flow. The number next to the abbreviation indicates the curve level, that is, the intensity of operation in the given mode.
Why does the circulation pump hum and buzz at night?
The most common cause is a setting that is too high. In the evening and at night, the thermostatic valves on the radiators are more closed, so the water pumped by the pump is forced through the restricted system, which can be heard in the pipes. Going down one curve or switching to proportional-pressure mode usually solves the problem.
Which pump mode should I choose for underfloor heating?
For underfloor heating, we recommend constant-pressure mode, usually marked CP, because underfloor heating loops require stable operating conditions. If you are unsure, a good starting point is to leave the factory setting, namely automatic mode.
How much electricity does a circulation pump use, and is changing the mode a noticeable difference?
Older three-speed pumps typically consume from several dozen to over ninety watts, depending on the speed, while modern electronic models consume from a few to several dozen watts. According to independent studies, simply changing from constant-speed mode to a regulated mode saves around thirty to fifty percent, and when the pump operates throughout the heating season, this makes a noticeable difference to the bill.
I changed the pump mode, but nothing improved. What next?
The pump setting determines the amount of water circulating throughout the entire system, but not how it is distributed among individual radiators. If, despite the correct mode, some rooms heat much less than others, the cause is usually the distribution of flow in the system, or air or contamination in it, rather than the pump itself.
