Circulating pump IBO does not drain water or make noise – solutions to common problems

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Circulation pump IBO does not discharge water or does not make noise – solutions to common faults

You get up in the morning, the radiators are cold, the pump is silent or makes strange noises – and you don't know where to start. Or on the contrary: the pump is running, you can hear it, but the heat just won't come into the house, the circulation is not working. I repeatedly encounter such situations with customers who have bought IBO circulation pumps and after some time run into one of the common operational faults. The good news is that most of these problems have a simple cause and an even simpler solution – if you know where to look.

This article will guide you through the most practical diagnostic procedure I know from real practice. We will go through the situation when the pump does not start at all, when it is running but the water is not moving, when it is noisy, vibrating, overheating, or when it is making unusual noises. Each case has its own logic – and if you understand that logic, you will be able to solve most of the faults yourself without the help of a service technician.

How a circulation pump works – the basis for understanding faults

Before we get into specific faults, let's briefly recap what a circulation pump actually does and how. A circulation pump in a closed heating circuit does not have the task of connecting water from a source or pushing it out – it simply moves it in a circle. It is essentially a very simple electromechanical device: an electric motor rotates an impeller placed directly in the medium, which creates a pressure difference that drives the water through the circuit. Since the water is closed in the system and should always be under pressure, the pump never runs "dry" – or at least it should not.

The IBO OHI series pumps have a wet-rotor motor – this means that the rotor rotates directly in the water and the water also serves as a lubricant for the bearings. This is an elegant solution that eliminates mechanical seals (shaft seal), reduces noise and prolongs the life. But precisely because of this, these pumps are sensitive to certain conditions – for example, dry running, air in the system or impurities in the medium.

From this basic understanding it follows that faults can be divided into two main categories: faults of the electrical part (the motor does not rotate) and faults of the hydraulic part (the motor is running, but the water is not moving). Many customers confuse these two situations and look for the cause in the wrong place.

The pump does not start at all – electrical diagnostics step by step

First situation: the pump is completely silent, no sound, no vibration, the outlet pipe is cold. This is a classic case where we have to start with the electrical side.

1. Check the power supply and fuses

This may sound trivial, but I estimate that in two out of ten cases the problem is right here. Check whether the circulation pump circuit is connected to a working socket or terminal block, whether the corresponding fuse in the distribution board is not blown, and whether the heating regulator (thermostat, room controller or boiler controller) is actually sending a signal to the pump. Many boilers have a built-in regulator that only switches the pump on when it is necessary to move the heating medium – and if the boiler is in summer mode or a low temperature is set, the pump simply receives the command "stop".

Practical tip: disconnect the control cable of the regulator and short-circuit the pump terminals manually (be careful, only if you know what you are doing and the system is de-energized). If the pump starts, the problem is in the regulator, not in the pump itself.

2. Blocked rotor – the most common reason for a silent pump after the holidays

This is by far the most common reason in my practice for why an IBO OHI circulation pump does not start at the beginning of the season. The OHI series pumps have a screw cap with a slot (usually a flat-head screwdriver 8–10 mm) on the side – or on the front side of the motor part. Behind this cap is the end of the rotor shaft. If the pump has not been running for several months (for example, during the summer), deposits of lime, magnetite or other minerals can mechanically block the rotor.

Procedure: Turn off the power! Unscrew the cap (be careful, a little water may leak out, have a cloth ready). Carefully turn the shaft manually with a flat-head screwdriver – you should feel that the rotor is moving, even with some resistance. Turn it once or twice back and forth, reattach the cap, turn on the pump – and in 80 % of cases the problem is solved.

If the shaft cannot be turned at all, the rotor is blocked by hard deposits. In such a case, it is necessary to dismount the pump, open the hydraulic part and mechanically clean or replace the impeller.

3. Burned motor winding or thermal fuse

If the pump still does not run after unblocking the rotor, the problem may be more serious. IBO OHI pumps have an internal thermal fuse (a thermistor or bimetal fuse) that disconnects the motor in case of overheating. Some reset automatically after cooling down (resettable), while others are one-time only. If the pump still does not work after a longer wait and cooling down, it is possible that the motor winding is really burned out – this is a case for replacing the pump or at least its motor part.

In such a situation, I recommend considering whether it is worth investing in repairing an older pump or rather proceed with replacing it with a new model. For example, the IBO OHI 15-60/130 is an affordable model suitable for smaller family homes and apartment circuits, where replacement is almost always more cost-effective than repair.

The pump is running, but the water is not moving – air in the system and other hydraulic causes

The second major group of faults: the motor is running, you can hear the typical quiet hum, maybe even slight vibrations, but the radiators remain cold and the flow in the pipes is zero or negligible. This is a hydraulic fault – the pump is rotating, but the power is not being transferred to the water.

Air in the system – the most common problem

Air in a closed heating circuit is an absolute classic. The pump is running in vain – the impeller is rotating in an air pocket instead of in water – and the water cannot move. Air most often enters the system after filling after the summer shutdown, during equipment replacement, during a leak and water refill, or simply gradually from dissolved oxygen in the water (corrosion).

Symptoms: the pump makes a louder, bubbling or crackling sound instead of a quiet hum. Radiators are cold, especially at the top. No heat can be felt on the outlet pipe (hot side).

Solution: Bleed the system. The procedure is as follows:

Check the pressure in the system on the boiler pressure gauge – it should be 1.0–1.5 bar when cold. If the pressure is low, add water through the filling valve.
Bleed the radiators – each radiator has a bleed valve (usually at the top right). Prepare a container, open the valve with a small wrench or screwdriver, and wait until water starts to flow out instead of air.
Bleed the pump itself: on the IBO OHI pump body, there is a bleed screw (usually the same as the shaft cover screw, or a separate screw at the top of the hydraulic section). Loosen it by a few turns, wait until water starts to drip, and then screw it back in.
Run the pump briefly, then repeat the radiator bleeding in order from the nearest to the farthest.
Check the pressure again and top it up if it has dropped.

Most customers who reported that the pump "does not work" solved this problem by bleeding the system within 20 minutes.

Closed valve or blocked valve

Another trivial, but surprisingly common cause: someone (installer, owner, neighbors in an apartment block) closed the ball valve on the supply or return pipe of the pump and forgot to open it. The pump is rotating in a closed space and cannot push the water anywhere. Check visually all valves and taps near the pump – they must be in the open position (lever parallel to the pipe).

Clogged filter (round filter/screen filter)

Before every circulation pump, a screen filter (angled filter, round filter) should be installed. If it is there and no one has ever cleaned it, the mesh may be completely clogged with magnetite, sludge, and coarse impurities. Result: the pump draws air instead of water, or the flow drops to a minimum.

Solution: Close the valves before and after the filter, remove the mesh insert, clean it under running water, and put it back in. Do this at least once a year, ideally before each heating season.

The pump is humming, vibrating, or making loud noises

Third category: the pump is working, the system is in operation, but it is accompanied by unpleasant noise. Customers describe various sounds – humming, whistling, knocking, bubbling, cracking. Each sound has a different cause.

Loud humming or vibrations

Loud mechanical humming is most often caused by the pump running at too high a speed setting for the given system. IBO OHI pumps mostly have three manually adjustable speed settings. If the pump is set to speed 3 (maximum) in a system where speed 1 or 2 would be sufficient, a turbulent flow, noise, and excessive pressure occur. Solution: reduce the speed setting. If the pump does not make much noise even at speed 1, it is fine.

Vibrations may also indicate mechanical wear of the bearings – in wet-running motors, the bearings (sliding) are cooled and lubricated by water, so if the water in the system contains a lot of sludge or abrasive particles, the bearings wear out quickly. This is manifested by a metallic squeaking or a sound similar to sand being ground.

Bubbling and cracking – cavitation

Cavitation is a phenomenon in which water boils locally due to low pressure at the pump inlet and forms vapor bubbles, which implode with a characteristic cracking or crunching sound when the pressure rises again (it sounds a bit like gravel in a drum). Cavitation is very harmful to the pump – it damages the impeller and the pump body.

Causes of cavitation in circulation pumps:

Too low a filling pressure in the system (less than 1 bar)
Too high a medium temperature (over 70 °C at low pressures)
Clogged filter before the pump
Too narrow a pipe at the pump inlet
The pump is placed too high in the system (in natural circulation, the temperature difference is not sufficient)

Whistling or high-frequency sound

Whistling can be caused by overdimensioned pressure created by the pump in relation to the network resistance – especially if some circuits are closed and the pump is "pushing against a wall". This is typical with thermostatic valves set to a low temperature or completely closed circuits. The solution is either to reduce the speed setting or to install a bypass valve (pressure relief valve), which diverts the excess flow.

The pump is overheating or the thermal fuse is repeatedly tripping

The thermal protection of the pump is the last safety net before physical damage to the motor. If the pump repeatedly trips and restarts after cooling down, it is a sign that something is wrong. Causes of overheating:

Dry running – the pump does not have enough water or there is air in the system. The wet-rotor motor is cooled by water – without water, it overheats very quickly, within minutes.
Blocked rotor – the motor draws current, but the rotor is not turning. The motor overheats within seconds to minutes.
Too high medium temperature – some IBO OHI models are designed for a maximum medium temperature of 110 °C (at operating pressure), but it is typically recommended to operate below 90 °C. If the boiler is not regulating properly and the temperature exceeds 100 °C, it can cause problems.
Electrical problems – unstable voltage, under-voltage or over-voltage can cause motor overheating.

Never install a bypass or replace the fuse when the thermal fuse repeatedly trips – this removes the protection and you risk burning out the motor or, in the worst case, a fire.

The pump is leaking – where to look for the leak

Small dripping from the pump is another problem I often encounter. Leaks can occur at several places:

Valve screw / shaft cover – if it is not seated properly or the sealing (O-ring) is damaged. Solution: tighten, or replace the O-ring if necessary.
Bolted connection between the motor and the hydraulic unit – these two parts are connected by bolts, with a sealing (rubber gasket or O-ring) between them. After mechanical intervention (unblocking the rotor), it is necessary to check that the bolts are properly tightened.
Flanged connections on the piping – the IBO OHI pump is connected to the piping via flanges (nuts), where there are seals. If the pump has been mounted and dismounted, the seal may need to be replaced.
Pump body – a crack in the cast iron or plastic housing of the hydraulic unit caused by freezing. If the system froze (e.g., a cottage, an unheated room), the pump body may be cracked. This cannot be repaired – the pump must be replaced.

Warning: never operate the pump with a visible leak. Water in the electrical housing can cause a short circuit, corrosion of the terminal block, and in the worst case, dangerous voltage on the metal housing of the pump.

Correct installation position – a source of many preventable faults

Surprisingly many faults occur simply because the pump is installed in the wrong position. Pumps in the IBO OHI series can be mounted horizontally (horizontally) or vertically (vertically), but the rotor axis must always be horizontal. In other words: the motor can point up, down, left, or right – but the shaft axis must be horizontal.

Why does this matter? The sliding bearings are lubricated by a layer of water. If the rotor is vertical (shaft axis vertical), the bearing is not evenly lubricated, one-sided wear occurs, and the pump has a significantly shorter lifespan. In addition, air accumulates precisely in the upper part of the system – if the pump’s inlet is at the top, the pump may suck in air instead of water.

If you have doubts about the correct installation, I recommend reading our separate article Installation of IBO Circulation Pump – Procedure, Position and Wiring, where the entire process is described in detail, including pictures of typical situations.

Preventive maintenance – what to do to avoid faults

From experience, I know that most IBO circulation pump faults are preventable. Here is a simple annual maintenance schedule that works:

Before the heating season starts (September – October)

Check the system pressure – it should be 1.0–1.5 bar when cold. Add if it is lower.
Clean the filter before the pump.
Test the pump, check if the rotor is turning (listen for vibration).
Bleed the radiators in the entire system.
Visually inspect the pump for leaks and corrosion.

During the season

Check the system pressure once a month.
If a new noise or vibration appears, diagnose it as soon as possible – small problems quickly become bigger.

After the season ends (April – May)

If you plan to turn off the pump during the summer, start it manually for 5–10 minutes every 2–3 weeks. This prevents rotor blockage due to sediment buildup.
Some boiler controllers have a "summer pump operation" function – they automatically start the pump briefly once a week. If your system has this function, activate it.

Selecting the correct model – even when replacing, consider whether to change the size

If you conclude that the pump needs to be replaced, it is also an opportunity to assess whether the original model was correctly dimensioned. Many faults (cavitation, noise, overheating) are caused by the pump being either too weak or, conversely, oversized for the system.

Basic decision: the size of the DN connection (15, 25, 32...) and the head (40, 60, 80 cm water column). For a typical family home with an area of 100–150 m² and a heating system made of copper or plastic piping DN 15–22 mm, a model with a coupling length of 130 mm and a head of 40–60 Pa is usually sufficient.

For example, the IBO OHI 25/40-130 is suitable for circuits with a DN 25 nominal diameter and a required head up to 4 m water column – typically a family home with a standard steel or aluminum heating system. For more demanding systems with longer piping or larger areas, you can choose a more powerful model such as IBO OHI 25/60-130 or for longer mounting distances IBO OHI 25/60-180.

If you are unsure about sizing, I recommend reading the article What performance does a circulation pump need for my house or What do the numerical designations IBO OHI mean – how to read technical parameters in our Knowledge Center.

Magnetite and corrosion – long-term enemies of circulation pumps

Magnetite deserves special mention – it is a black sludge-like deposit that accumulates in every older steel heating system. Magnetite is formed by the corrosion of steel pipes and steel radiators. Its particles are very fine (micrometric in size), so they pass through standard filters and get into the pump. In the pump, they cause:

Wear of sliding bearings (abrasive effect)
Settling on the impeller and reducing its efficiency
Blocking the rotor (magnetite can fuse together after long periods of inactivity)
Clogging of thermostatic valves

Solution: install a magnetic filter (magnetic sludge separator) before the pump. These devices capture magnetite particles on a strong magnet, and by regularly cleaning the separator (once a year), you remove them from the system. In systems older than 15 years with steel piping, a magnetic filter is almost essential.

For a radical reduction in magnetite and other impurities, a chemical system flush (inhibitors + flush) can also be performed. This is a larger investment, but it significantly extends the lifespan of the entire system, including the pump.

When is the pump really beyond repair

Not every pump is worth repairing. Here is my practical view: if the pump is older than 10–12 years and any serious fault occurs (burned winding, cracked housing, broken impeller), replacement is more economical than repair. Spare parts for older pumps are hard to find, and the cost of a service technician's labor can be equal to the price of a new pump.

IBO OHI pumps are very affordable – for example, the IBO OHI 25/40-180 is a compact solution with a 180 mm connection length at a price that makes repairing an older unit simply not worthwhile. Replacing the pump is also a job that takes 1–2 hours for an experienced plumber, or even for a skilled DIY enthusiast.

Most frequently asked questions (FAQ)

Why does the IBO pump start in the morning but stops in the evening and doesn't restart?

The most likely cause is a thermal fuse. For some reason, the pump overheated during the day (air in the system, blocked rotor, excessively high medium temperature), the thermal fuse disconnected it, and when it cooled down, the fuse restored power – that's why it runs in the morning. During the day, it overheats again and stops in the evening. I recommend immediate diagnostics: check the system pressure, bleed the system, check the filter and medium temperature. If the fault recurs, the pump or system needs to be examined in more detail.

The IBO OHI pump ran quietly for years, now it makes a loud noise – what happened?

A change in sound from a previously quiet pump most often indicates one of three things: air in the system (gurgling sound), worn bearings (metallic grinding or crunching), or deposits in the hydraulics (whining during movement). Try bleeding the system first – it's free and quick. If the noise persists, the pump likely needs service or replacement.

Can I use the IBO circulation pump in summer for hot water circulation?

IBO OHI series pumps are primarily intended for closed heating circuits with clean water without aggressive additives. For circulation of potable hot water (TUV – hot domestic water), you must use a pump certified for potable water (hygienically approved). Standard OHI models for closed heating circuits are not suitable for contact with drinking water. For this purpose, there are separate circulation pumps with the appropriate certification.

I forgot to turn off the pump before winter and the water in it froze. What now?

If the water in the pump froze, the hydraulic housing (cast iron or plastic) likely cracked due to ice pressure. Visually inspect the pump for cracks. A leak after thawing will be obvious. A pump damaged in this way cannot be repaired – it must be replaced. In the future: if it's an unheated cottage or a weekend home, the system should be drained before winter, or you should install frost protection (thermostatic valves, electric heating cables to prevent freezing).

On which speed setting should I set the IBO OHI pump for a typical family home?

Start at level 2 (medium speed) and monitor the result. If all radiators are evenly warm and the system is not making noise, this is the correct setting. If distant radiators are weak, try level 3. If the pump is humming or all radiators are too hot, try level 1. The goal is to achieve quiet operation and even heating at the lowest possible setting – it saves energy and extends the pump's lifespan.

Do I have to drain the entire system when replacing the pump?

Not necessarily. If there are ball valves installed before and after the pump (which every properly installed system should have), it's enough to close these valves, place a container under the pump, unscrew the bolts, and replace the pump. Only the water trapped between the valves will drain from the system – usually 0.5–1 liter. Then you just refill the system, bleed it, and restart it. If the valves are missing, pump installation is an ideal opportunity to install them.

Conclusion: most faults have simple solutions

After reading this article, you should have a clear picture of how to systematically approach IBO OHI circulation pump faults. I summarize it into a few basic principles that apply to 90% of cases:

If the pump is silent – check the power supply, fuses, and regulator. Then try to unblock the rotor. Only consider a burned motor as a last resort.

If the pump is running, but the water isn't rising – bleed the system and check the pressure. Check the valves and filter. It's almost certainly air or a closed valve.

If the pump is humming or vibrating – reduce the speed setting. Check for cavitation (low pressure, clogged filter). If there is a whining sound, consider worn bearings.

If the pump is leaking – check and tighten the seals. Be careful of a cracked housing due to freezing.

Regular preventive maintenance – checking pressure, cleaning the filter, bleeding the system at the start of the season, and occasional operation in summer – is the cheapest insurance against most of these situations. And if you still decide to replace the pump, the full range of IBO OHI circulation pumps is available at atria.sk in the IBO pumps category.

Do you have a question about this topic?

Not sure or dealing with a specific situation in your home? Write to us – we're happy to help.