Annual Maintenance and Service of Grundfos Pumps – What to Check Every Year

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Annual maintenance and service of Grundfos pumps – what to check every year

Grundfos pumps are among the most reliable products in their category. In practice, we come across units that run without problems for fifteen, twenty or even more years – but only if someone regularly takes care of them. And it is precisely here that most households and operators fail. The pump is forgotten, it gets covered with limescale, it gets clogged with deposits, corrosion does its job – and one day in January, when it is freezing outside, the system stops working. That is when people start looking for service companies, spare parts or even entirely new pumps.

This article is a practical guide to annual preventive maintenance of Grundfos pumps – circulation, solar and submersible drainage pumps. You will find here specific procedures, values to focus on, what to measure and what to replace. Not theory, but what really works in practice after years of work with hundreds of installations.

Why regular pump maintenance is important at all

Many customers ask whether it is even necessary to check the pump annually if it is working and there are no signs of a problem. The answer is clear: yes, and for several reasons.

First, most pump failures do not occur suddenly, but gradually. A bearing slowly wears out, a mechanical seal starts to leak, a rotor gets clogged with deposits – all of these are processes that develop over months. If you catch them in time, the repair will cost you just a few euros. If you overlook them, you will end up replacing the entire pump at an inconvenient time.

Second, the pump has a direct impact on the energy efficiency of the entire system. A circulation pump with a clogged rotor or incorrectly set speed level can consume 20–40 % more electricity than necessary. These are real extra costs every month on your electricity bill.

Third, in cases such as solar systems or heating systems with a boiler, a pump failure can have a cascading effect – overheating of collectors, freezing of the system, boiler damage. Preventive maintenance is therefore protection of the entire investment, not just the pump itself.

Annual inspection of circulation pumps – complete procedure

Circulation pumps are the heart of every heating system. These include models such as GRUNDFOS UPS 25-30, as well as newer energy-efficient types. Their annual inspection should ideally be carried out in spring, after the heating season has ended, or in autumn before it begins.

1. Visual inspection and leak check

Start with what you can see. Inspect the entire pump and its surroundings. Look for:

Signs of water leakage – limescale stains, rust streaks or wet areas on the pump housing, on flanges, on the piping before and after the pump.
Corrosion on the pump body or on flange screws – if the steel housing, flange screws or fittings are rusty, it is a sign that something is wrong with the water quality or the pH of the system water.
Cracked or hardened sealing – in older models, rubber seals become brittle. Press it with your finger – soft, elastic rubber is fine, hard and cracking rubber must be replaced.
Condition of cable insulation – near the boiler, heat can damage insulation over time. Any burned, cracked or melted insulation must be addressed immediately.

In practice, we have encountered cases where a customer ignored a small drip near the pump flange for years. At first glance, nothing serious – just a few drops per day. After four years, the flange was corroded so badly that it could not be tightened without replacing the entire pump. Meanwhile, a timely replacement of the seal would have cost just a few euros and fifteen minutes of work.

2. Checking sound and vibrations

Turn on the pump and listen. A healthy Grundfos circulation pump operates almost silently – only a very soft sound of the fluid circulation. Any deviations are a warning:

Metallic whining or squeaking – worn bearing or foreign object in the rotor (limescale fragments, rust particles).
Strong vibrations in the piping – unbalanced rotor, jammed rotor blades, or air in the system.
Gurgling or bubbling – cavitation, which occurs at insufficient pressure at the inlet, air in the system or excessively high fluid temperature.
Humming at higher speeds – common in older non-inverter models, but if the humming gets worse, it indicates a deteriorating bearing.

A good tool is to place a long screwdriver against the pump housing and hold the handle to your ear – an improvised stethoscope that amplifies every unusual sound from the bearings.

3. Checking the speed setting and performance

Classic Grundfos circulation pumps such as the UPS have three fixed speed settings (1, 2, 3). Check whether the pump is set to the correct setting according to the system design – many installations unnecessarily run at the third speed even in summer or during transitional weather, which means energy waste. If you are unsure what speed is optimal for your system, see our article How much Grundfos pump power do I need for my house.

For modern electronic pumps (Alpha, Magna), it is also necessary to check the setting of the control curve. These pumps can automatically adjust performance, but only if they are correctly configured. A poorly set curve can cause noise from thermostatic valves or insufficient circulation in distant parts of the system.

4. System air venting

Air in the system is a chronic problem, especially after topping up water, after repairs or simply after a long period of operation. Air pockets accumulate in higher parts of the piping and reduce circulation efficiency.

Air venting procedure for Grundfos circulation pump UPS:

Turn off the pump.
Locate the vent screw on the front cover of the pump (it is usually marked or you can recognize it by a small plastic cover or a slot for a flathead screwdriver).
Place a cloth or a container – some water may flow out during venting.
Loosen the screw by half a turn – wait until the air escapes and water starts to flow without bubbles.
Tighten the screw and start the pump.

Repeat this process until the pump starts operating smoothly without bubbles.

Annual inspection of Grundfos solar pumps

Solar pumps operate under much more demanding conditions than conventional circulation pumps. They circulate a non-freezing mixture (usually propylene glycol or ethylene glycol solution) at high temperatures – in summer, the temperature at the collector outlet can reach 80–100 °C, and even higher in stagnation. All of this places increased demands on the pump and the entire system.

Models such as GRUNDFOS Solar 25-120 or the smaller GRUNDFOS Solar 15-80 are specifically designed for these conditions – they have suitable seals, durable materials, and electronics adapted to solar regulators. Despite this, they require annual maintenance.

Inspection of the non-freezing mixture

This is probably the most important point in the maintenance of a solar system. The non-freezing mixture degrades over time – repeated heating breaks down corrosion inhibitors, pH changes, and the mixture loses its protective properties. Many solar pump failures we have encountered in practice were caused precisely by degraded heat transfer medium, not the pump itself.

Every year, you should:

Measure the pH of the non-freezing mixture using a test kit or pH meter. The correct pH value for propylene glycol in solar systems is usually 7.5–9.0. A drop below 7 indicates an acidic environment that actively corrodes metal parts, including the pump rotor.
Measure the glycol content using a refractometer – a simple tool that will show you at what temperature the mixture will freeze. Depending on the climatic location, it should withstand at least −25 to −30 °C, which corresponds to approximately 35–40 % glycol content.
Check the color and odor – a healthy mixture is clear or has a slight greenish tint (if it contains dye). A dark brown, cloudy, or unpleasantly smelly mixture is a signal for immediate replacement.
Check the expansion tank reservoir – if the tank is over-pressurized with air or incorrectly pressurized, cavitation in the pump can occur at high temperatures.

System pressure check

The pressure in the solar system in the cold state (before starting, at room temperature) should normally be 1.5–2.5 bar – the exact value depends on the height of the system and the setting of the expansion tank. A drop in pressure below the minimum indicates a leak or a problem with the expansion tank. Excessively high pressure can cause the safety valve to open and result in the loss of the non-freezing mixture.

Always perform the measurement in a cold system – never during hot operation, when the pressure is naturally higher due to the thermal expansion of the liquid.

Cleaning of magnetic filter and dirt filter

If your solar system has a magnetic filter (and if it doesn't, we recommend adding one), it should be cleaned every year. Metal particles from pipe corrosion, seals, and other components accumulate on the magnet and can enter the pump rotor. In practice, we have removed clusters of iron oxide as large as peas from magnetic filters, which could block the pump rotor within a few months.

Steps for cleaning the magnetic filter:

Close the shut-off valves before and after the filter.
Depressurize and drain the section.
Unscrew the magnetic rod – place a piece of paper or a handkerchief to collect magnetic particles as you slide them off the magnet.
Rinse the body of the filter, check the mesh insert and clean or replace it as needed.
Reassemble, open the valves, and bleed the system.

Annual inspection of submersible drainage pumps

Submersible pumps such as GRUNDFOS UNILIFT KP 150 A1 or the more powerful model GRUNDFOS UNILIFT KP 250 A1 have specific maintenance requirements. They are used to pump out floodwater, rainwater from pits or underground areas, and usually operate in environments with sandy sediments and organic matter.

Inspection and cleaning of the suction basket and rotor

The suction basket (lower grid) is the first line of defense for the rotor against foreign objects. It should be inspected and cleaned in case of contamination (leaves, sand deposits, organic sludge). The rotor is also affected by sand deposits – fine sand passes through the basket and abrades the rotor blades. After several seasons, the rotor may show visible wear.

For Grundfos UNILIFT submersible pumps, rotor inspection is straightforward:

Disconnect the pump from the electrical supply.
Remove the pump from the pit or shaft.
Rinse it under running water.
Unscrew the lower suction cover – usually 3–4 screws.
Visually inspect the rotor – check for blade wear, cracks, or foreign objects.
The rotor should turn freely when manually rotated – if it resists, it may be clogged or the bearing is damaged.

Float switch inspection

The float switch is a critical component of automatic submersible pumps. If it does not function properly, the pump either does not start (and the pit fills up) or runs dry without water, which quickly damages it. Check the following annually:

Free float movement – must not be stuck against the shaft wall, cable or any other object.
Float cable condition – check for mechanical damage or breakage at the bend.
Functionality – manually lift the float to the ON position and verify that the pump starts.

Checking the cable and plug

The submersible pump cable operates in harsh conditions – wet environment, bending during lifting and lowering, UV radiation (if part is above ground). Moisture can penetrate the motor through the cable or plug – which is usually fatal for the pump motor. Check the entire length of the cable for mechanical damage. If the plug is wet, damaged or you see oxidation on the contacts, replace it before a failure occurs.

Water quality and its impact on pump lifespan

One of the most underestimated factors affecting the longevity of Grundfos pumps is the quality of water in the system. Hard water (with high calcium and magnesium content) causes limescale deposits on the impeller, volute casing and heat exchangers. An impeller with a thick layer of limescale can have a third smaller channel diameter, significantly reducing pump performance – while motor current increases.

We recommend in practice:

Measure water hardness once a year – simple test strips can be purchased at any pool store. If hardness exceeds 300 mg/l CaCO₃ (about 17 °dH), consider softening the filling circuit.
Maintain correct pH of system water – the optimal value for closed heating systems is 8.0–9.5 (a slightly alkaline environment suppresses corrosion).
Use corrosion inhibitors – in closed systems, add an approved inhibitor mixture according to the manufacturer's recommendations (e.g., molybdate or phosphonate-based inhibitors).
Minimize water top-up – every water addition to a closed system brings new minerals. If you top up more than 5–10 % of the volume annually, look for a leak.

Electrical inspection – what is most often overlooked

The electrical side of the pump is an area where many owners have no idea what and how to check. And yet, electrical faults are among the most dangerous – they can cause fire, electric shock or silent failure without warning.

Measuring insulation resistance

The insulation resistance between the motor winding and the pump housing should be in the order of megaohms (MΩ) for a healthy pump – typically 100 MΩ or more for a new pump, and at least 1 MΩ for an old one. If it drops below 1 MΩ, the winding is wet or degraded and motor failure is imminent. Perform the measurement using a megohmmeter (megger) – this is usually done by an electrician or service technician under domestic conditions.

Checking protective earthing

Verifying that the pump is properly earthed is a basic safety check. For pumps in wet environments (submersible pumps, humid boiler rooms), it is literally a matter of life and death. Check the tightness of the earthing conductor terminal, absence of corrosion on the terminal and integrity of the green/green-yellow conductor.

Current draw

The actual current draw of the pump motor (measured with a clamp meter) is an excellent diagnostic indicator. Each model has its rated current values (A) for each stage listed on the nameplate. If you measure significantly higher current:

The impeller is mechanically jammed or slowed by deposits.
The bearing is worn and offers higher resistance.
The winding is partially short-circuited.

If the current is instead too low under full load, the pump is not pumping – it is either not submerged or there is air in the system.

What should be part of the annual service record

A good service technician – as well as a conscientious owner performing their own maintenance – should record measured values in the pump's service record annually. The record allows you to track trends: if the current draw increases by 0.1 A every year, after three years you will know something is happening – and you can act before a failure occurs.

Recommended content of the service record:

Date of inspection
Pump model and serial number
Speed setting (or curve for electronic pumps)
Measured current (A) at each stage / under nominal load
System pressure (cold)
pH of system water / antifreeze mixture
Condition of seals and flanges (OK / leaking / replaced)
Condition of cables and grounding
Performed tasks (venting, cleaning, seal replacement...)
Recommendations for further service

When a Grundfos pump is approaching the end of its life and needs to be replaced

Even with regular maintenance, there comes a time when it is worth replacing the pump before it completely fails. Signs that the pump is nearing the end of its life:

Age over 15–20 years with continuous operation – bearings, mechanical seals, and winding insulation have a finite lifespan.
Repeated failures within 2–3 years – if the same or a similar failure recurs, the pump is systematically worn out.
Repair cost exceeds 50–60 % of the price of a new pump – it is no longer economically viable to repair.
Extremely high electricity consumption compared to newer models – older UPS pumps without electronic regulation can consume 3–5× more electricity than new ECM pumps at the same performance level.

If you are considering a replacement, take a look at our article How to choose the right Grundfos circulation pump for heating or the comparison Grundfos UPS vs. Grundfos solar pumps – which is suitable for your system. For the installation of a new pump, a detailed step-by-step guide is also available in the article Grundfos circulation pump installation step by step.

Common mistakes in Grundfos pump maintenance that repeat

After years of service experience, we have noticed that certain mistakes almost repeat with every second customer. These are mistakes that are understandable for various reasons – lack of information, established myths, or the desire to save money.

Oiling the pump – Grundfos circulation pumps with wet rotors (most models) are lubricated by the circulating liquid. Never oil them with oil or other lubricants from the outside. In practice, we encounter pumps where someone injected WD-40 into the vent screw "to prevent rusting" – this can damage the seal and contaminate the system.
Switching off the pump during summer – long-term idling leads to rotor seizing. If you do not need the pump in summer, let it run briefly at least once a month (or activate the antiblocking function if available).
Ignoring a small leak – "It's just dripping a little, but it's working" – see the example above. A small drip is always a sign of something bigger to come.
Filling the system with hard water without treatment – see the section on water quality.
Incorrectly set expansion tank – too low air pressure in the tank causes the pump to work on the edge of cavitation, which dramatically shortens its lifespan.

Preventive replacement of spare parts – what to have on hand

A resourceful owner who wants to minimize downtime should have a few basic spare parts and tools on hand:

A set of O-rings and flat gaskets suitable for the flanges of the pump (plastic gasket packs usually cost up to 5 €).
Teflon tape or pipe thread sealant paste.
A test kit for pH and a refractometer for checking the antifreeze mixture (for solar systems).
Clamp-on ammeter – a simple model costing up to 30 € is invaluable for diagnostics.
A supply of corrosion inhibitor for closed systems.

Frequently asked questions (FAQ) about Grundfos pump maintenance

How often should a Grundfos UPS pump be serviced in a typical family home?

At least once a year – ideally in spring after the heating season ends. The inspection includes a visual check, venting, checking the seals, measuring the current, and setting the speed stage. If you have an older house with hard water or a system without inhibitors, we recommend checking every 6 months.

My Grundfos UPS 25-30 is making noise and the vibrations are more noticeable than before – what should I do?

The most common cause is air in the system or a clogged rotor. Start by venting the pump and the entire system. If the problem persists, try manually venting the pump through the vent screw. If it still makes noise after venting, check the rotor – in older pumps, the bearing may be worn. A more detailed procedure can be found in the article Grundfos pump not pumping or making noise – causes and solutions.

How long will a Grundfos Solar pump last with regular maintenance?

Grundfos Solar pumps are built for harsh conditions and can last 12–18 years or more with proper maintenance. It is key to check and replace the antifreeze mixture annually and, if necessary, completely replace it every 3–5 years, while maintaining the correct pH and pressure. Degraded antifreeze is the most common reason for premature end of a solar pump's life.

Can I disassemble and clean the rotor of a Grundfos UNILIFT pump myself?

Yes, as long as you follow safety precautions – the pump must be disconnected from the power supply and removed from the pit. The lower suction cover is usually unscrewed with 3–4 screws, the rotor is accessible and can be cleaned. Avoid using hard metal tools directly on the rotor blades – you could damage them. For removing hard deposits, use citric acid or a specialized limescale remover.

Why won't my Grundfos pump start after summer?

A classic problem of a seized rotor after long idling. The rotor can seize if the pump has been idle for several months and mineral deposits have "glued" it in place. Solution: turn off the pump, locate the venting / unlocking screw on the front cover, and use a special screwdriver to turn the shaft (some models have a notch for this). If this fails, the pump must be taken to a service for mechanical release. In the future, activate the antiblocking function or run the pump for 15 minutes at least once a month.

How much does annual pump maintenance cost with a service technician?

For a simple Grundfos circulation pump in a family home, expect to pay 40–80 € for the technician's labor (depending on the region and scope). If spare parts (seals, inhibitor) are needed, add another 10–30 €. For solar systems with sampling and fluid testing, it can be 80–150 €. DIY maintenance according to this guide will cost you the price of test kits, which is in the range of 10–20 € per year – but electrical diagnostics should always be done by a professional.

Conclusion: Maintenance as an investment, not an expense

Every hour spent on preventive Grundfos pump maintenance will pay off many times over – either by extending the life of the equipment, improving energy efficiency, or simply by ensuring the system does not fail exactly when you need it most. Grundfos built its reputation for reliability on quality construction – but even the best construction will eventually succumb to time without proper maintenance.

If, after reading this article, you realize your Grundfos pump has never received a real inspection, start now. Schedule an hour in the boiler room in spring or autumn, prepare your notebook and measuring tools, and go through each point one by one. If you find anything, you have the chance to address it for a few euros and a few hours – not for hundreds of euros in an emergency call in the middle of winter.

Further practical information on faults and their solutions can be found in the articles Common Grundfos pump faults and how to fix them and Frequently asked questions about Grundfos pumps in our Knowledge Center.

Do you have a question on this topic?

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