How to connect a Grundfos UNILIFT pump – installation procedure
How to connect a Grundfos UNILIFT pump – complete installation step by step
Grundfos UNILIFT pumps are among the most popular submersible pumps on the Slovak market. You will find them in basements, shafts, for pumping rainwater, in garden tanks, and for pumping water after a water pipe failure. Their popularity is not accidental – they are robust, reliable and relatively easy to install. Despite this, the same mistakes are repeated when they are connected, which shorten the pump's lifespan or even cause dangerous situations. This article will take you through the entire installation process from choosing a location, through mechanical connection to electrical connection and the first test run.
If you are looking for information about a circulation pump for heating or a solar system, I recommend looking at the articles Installation of Grundfos circulation pump step by step or Grundfos solar pumps – what they are and how they work. This text is exclusively about submersible UNILIFT pumps designed for pumping clean or slightly contaminated water.
What is the Grundfos UNILIFT pump and where is it used
The UNILIFT series includes several models of submersible pumps with different power and configuration. The basic division is into KP models (compact submersible pumps) and CC models (pumps with suspended motors). For home users, the most relevant models are GRUNDFOS UNILIFT KP 150 A1 and GRUNDFOS UNILIFT KP 250 A1 with a 10 m cable.
Typical uses include:
- Pumping water from a flooded basement or cellar
- Draining garden ponds or swimming pools
- Pumping rainwater from a collection tank
- Draining construction pits and excavations
- Pumping from cleaning shafts and inspection chambers
- Garden irrigation with a larger volume of water
The KP 150 A1 model has a maximum head of 5 meters and a maximum flow of 7,000 liters per hour at zero back pressure. The KP 250 A1 is more powerful – it achieves a head of up to 8 meters and a flow of 9,000 l/h. The difference is not only in performance, but also in construction – the KP 250 has a more robust assembly and a longer standard cable (10 meters), which is an advantage in deeper shafts.
What you need before starting the installation
Preparation is half the success. Before you start the actual installation, prepare the following:
Tools and materials
- Flange or coupling matching the pump's discharge port (G 1½" for KP 150, G 2" for KP 250)
- Hose or rigid pipe of appropriate diameter (at least 1½" for KP 150, 2" for KP 250) – for shorter distances, a garden hose is sufficient, for longer distances over 10 meters, I recommend a rigid PVC pipe
- Check valve on the discharge side (not necessary, but significantly extends the pump's lifespan in intermittent operation)
- Rope or chain for lowering the pump – never lower the pump by the cable only
- Floating switch (if the pump does not have a built-in one, which depends on the model)
- Sealing tapes (teflon) and conical seals for threaded connections
- Multimeter to check the electrical connection
- FI protective switch 30 mA – mandatory when working with electrical appliances in a wet environment
Electrical requirements
UNILIFT KP pumps are single-phase, 230 V / 50 Hz. KP 150 has a power of 450 W, KP 250 has a power of 750 W. Both models are delivered with a connected power cable ending in a plug – for KP 250, the standard cable length is 10 meters, which covers most common shafts and cellars without the need for an extension cable.
Important warning: The pump must not be connected to a regular socket without an FI switch (residual current device). In a wet environment, this is an absolute necessity, not just a recommendation. If your home electrical installation does not have FI protection on that circuit, use a portable FI adapter or have the electrical installation modified by an electrician.
Mechanical installation of the UNILIFT pump step by step
Step 1: Preparation and inspection of the installation site
Before starting the pump in the shaft or tank, check the water depth and the nature of the liquid being pumped. UNILIFT KP pumps are designed for clean or slightly contaminated water. The maximum size of solid particles that can pass through the pump without damage is 5 mm for KP 150 and 10 mm for KP 250. If you are pumping water with a higher amount of sand or coarser impurities, consider using a coarse mesh filter.
The bottom of the shaft or pit should be firm. The pump must not lie freely on a muddy bottom, as it could sink into the sludge and block the water inlet (and at the same time block the float switch). Ideally, support the pump with stones or a small brick so that the suction openings are at least 3 cm above the bottom.
Step 2: Connecting the discharge hose or pipe
The discharge nozzle of the UNILIFT KP pump has an external thread. For KP 150 it is G 1½", for KP 250 it is G 2". Apply Teflon tape to this thread and screw on the appropriate hose connector or flange adapter. Do not tighten too much – the cast iron or plastic body of the pump can crack under excessive torque.
I recommend installing a check valve as close to the pump as possible on the discharge hose (ideally right after the discharge nozzle). The check valve prevents water from flowing back from the pipe into the shaft after the pump is turned off. Without it, the pump must overcome the weight of the entire column of water in the hose at each start, which significantly strains the motor and shortens its lifespan.
When choosing a hose, make sure that its inner diameter is not smaller than the pump's discharge nozzle. Narrowing the hose is one of the most common mistakes I see in customer installations – the customer buys a G 2" pump and connects a garden hose of ¾", the performance drops to a third and the pump overheats.
Step 3: Securing the rope or chain
You will find an eye on the pump body for hanging. Thread a stainless steel rope or chain through this eye and tie it securely. Secure the other end to a fixed point on the edge of the shaft (hook, clamp, crossbar). The rope should be long enough for the pump to reach the required depth, but not so loose that it twists and gets tangled with the hose or electrical cable.
Never lower the pump by the electrical cable. The cable is not designed to bear the mechanical load of the pump's weight. Its insulation can be damaged at the edges of the shaft, and an electric shock in a wet environment can be fatal.
Step 4: Setting up the float switch
Most UNILIFT KP models come with an integrated float switch or the option to connect one. The float determines the minimum water level at which the pump operates. When the water level drops below the set level, the float turns off the pump and prevents so-called dry running – a condition in which the pump runs without water, which quickly destroys it (the mechanical seals are cooled and lubricated by the pumped water).
You adjust the position of the float by shortening or extending the float cable (depending on the model). The minimum water level at shutdown should be such that the suction nozzle is always submerged at least 5 cm below the surface. For KP models, the integrated float is factory-set, but check its position – in shafts with irregular walls, it may get caught on a protrusion and stop functioning properly.
Step 5: Routing the hose and electrical cable
The hose should lead to the discharge point (outlet, tank, garden) with a smooth upward slope and without air pockets. If the hose has any upward bend in the route (up and down a hill), an air pocket will form, which reduces flow and can cause a suction effect when the pump is turned off. Where possible, route the hose smoothly without turns.
Route the electrical cable along the edge of the shaft so that it does not hang freely in the middle – it could get caught on the pump or float. At the top edge of the shaft, secure the cable with a clamp so that it does not go back down to the pump.
Electrical connection of the UNILIFT pump – safety first
UNILIFT KP pumps come with a connected cable and plug – in the basic scenario, you simply plug the plug into the socket. But this is not enough for safe operation. Here is what you need to check:
FI protective switch – an absolute requirement
Every electrical device operated in a wet environment must be protected by a residual current device (FI switch) with a sensitivity of maximum 30 mA. This is required by the valid standard STN 33 2000-7-701 and is also common sense – in the event of a cable insulation fault, current can pass through the water to the operator's body. The 30 mA FI switch will detect this and turn off the circuit before a fatal electric shock occurs.
If your basement socket does not have FI protection, buy a portable FI adapter (so-called FI socket) or have your electrical installation modified by an electrician. The cost of an FI adapter is only a few dozen euros – much less than the cost of treating an electric shock.
Extension cable – only if necessary and the right one
If the standard cable length is not sufficient, use an extension cable with a cross-section of at least 1.5 mm² for KP 150 and 2.5 mm² for KP 250. A smaller cross-section will cause voltage drop, the motor will operate below nominal voltage, will overheat and its lifespan will be shortened. The extension cable must have at least IP44 protection – common household extension cords are not allowed.
Cable couplings must be kept out of a wet environment. Never connect the cable inside a shaft or in a flooded room. Each connection must be in a dry environment, in a box with an IP65 protection rating.
Earthing and protective conductor
The pump cable has three conductors: phase (L – brown or black), neutral (N – blue), and protective conductor (PE – yellow-green). The protective conductor is connected to the protective contact of the socket. The socket must be earthed. If you use an old double socket without earthing (for example, in an older basement without renovation), you cannot operate the pump safely without prior repair of the electrical installation.
First test run and functionality check
Before the first start-up, make sure that:
- The pump is fully submerged in water – at least the suction inlet must be below the water level
- The float switch is free and can move without obstruction
- The discharge hose is not kinked or twisted
- The rope is taut (the pump is hanging, not touching the bottom with mud)
- The residual current device (RCD) is connected and functional (test with the TEST button on the RCD)
After plugging in the plug, the pump should start immediately. Listen to the motor sound – normal operation is a uniform hum without rattling. Rattling or grinding indicates the presence of solid impurities or bearing failure. Check whether water is actually flowing through the discharge hose – on the first start-up, it takes a few seconds for the hose to fill, after which the flow should be stable.
Test the float switch: lift the float manually upwards – the pump should turn off. Lower it again – the pump should turn on again. If it does not work, check the float cable and its connection.
Installation in a shaft for permanent operation – long-term solutions
If you plan to operate the pump for a long time (for example, permanently in a basement drainage shaft), a few additional things need to be done compared to one-time use:
Permanent installation of the discharge pipe
For permanent operation, replace the hose with rigid PVC piping. Hoses age, crack in the cold, and it is harder to prevent air pockets. PVC piping with fixed joints and the correct slope ensures optimal flow at all times. Route the pipe with a smooth upward slope towards the outlet and install a bleed valve at the highest point.
Standby pump or alarm
If a pump failure during permanent operation would cause flooding (for example, a basement of a family house above the groundwater), consider installing a standby pump at a higher level or a water level alarm. A water level alarm is a simple and inexpensive device – a piezo siren with a float probe that sounds when the water level rises above the set limit.
Regular inspection and cleaning
For permanent operation, inspect once a year: the condition of the suction strainer (clean from deposits), float mobility, condition of the electrical cable (cracks in the insulation, corrosion of the plug connector), functionality of the RCD (test with the button). More about regular maintenance can be read in the article Maintenance and service of Grundfos pumps – what to check every year.
Common installation errors with UNILIFT – what I repeatedly see in practice
Over the years of working with pumps, I have encountered several errors that repeat so regularly that it is worth explicitly listing them:
- Pump on the bottom without support – when the pump sinks into the mud, the remaining sediment clogs the suction inlet and the float cannot float. Result: the motor runs dry and burns out within an hour. Always support it.
- Cable and rope entanglement – when the customer throws the pump down, the cable wraps around the rope, and during lifting, the cable is pulled and damaged. Lower slowly, keep the cable and rope separate.
- Hose restriction – already mentioned, but so common that it is worth repeating. G 2" discharge and ¾" garden hose is a crime against the pump.
- Missing check valve at higher discharge heights – at discharge heights over 4 meters and without a check valve, the motor is overloaded at every start. If the pump starts 50 times a day, it is worn out in a month as if it had been used for a year.
- Extension cord in a flooded room – more than once I have seen an extension cord lying in water. That is Russian roulette. Cable connections and sockets must be dry.
- Ignoring the warning signal of rattling – the customer lets the pump run despite the rattling "because it is still pumping". Rattling means damage and operation will end with total failure in a few hours, not in years.
Differences in installation of UNILIFT compared to Grundfos circulation pumps
If you are used to circulation pumps for heating such as GRUNDFOS UPS 25-30 or solar pumps GRUNDFOS Solar 25-120, you should know that the installation of UNILIFT is different in many ways:
Circulating pumps such as the UPS 25-30 are installed horizontally into a closed heating circuit, where there is no issue with sealing against the atmosphere or float switches. Submersible pumps UNILIFT are designed for open systems, where they pump water from a source somewhere else. If you are interested in a more detailed comparison of Grundfos pump types, read the article Grundfos UPS vs. Grundfos solar pumps – which one is suitable for your system.
Installation in a basement – a practical scenario from practice
The most common scenario I deal with is a customer with a basement into which groundwater seeps during snow melting or heavy rain. The basement has a concrete floor, and in the corner there is a sump or a manually dug pit with a depth of 30–50 cm. The customer wants the pump to operate automatically, without the need to be at home.
The solution looks like this: The UNILIFT KP 150 A1 is lowered into the pit (this is sufficient in terms of capacity for basements up to 80 m²), a 40 mm PVC pipe is connected to the discharge port, leading through the wall outside to the garden or into the sewer. The float switch is set to turn the pump on at a water level of 15 cm and off at 5 cm. A water level alarm is mounted above the sump as a backup in case of pump failure. The entire installation is powered through a 30 mA FI adapter plugged into an outlet located 1.2 meters above the floor (out of reach of potential flooding).
This solution works for years without intervention – the customer only checks the float and FI protection once a year. For larger areas or deeper pits, I would go for the GRUNDFOS UNILIFT KP 250 A1 with a 10 m cable – the long cable is an advantage because the outlet can be far from the pit without the need for an extension cable.
Installation for rainwater pumping – garden tank
The second common scenario is an underground garden tank for rainwater with a volume of 3,000 to 10,000 liters. The customer wants to pump water for garden irrigation. Here are a few specifics:
The tank is usually plastic, with one inspection opening of 50–60 cm in diameter. The pump is lowered into the tank through this opening – it is therefore important to check in advance that the pump fits through the opening (the dimensions of the UNILIFT KP are compact, and most openings are sufficient).
Water in the garden tank is usually cleaner than in a flooded basement, but it may contain leaves and biological material. I recommend installing a finer suction strainer or a filter basket before the pump. Set the float switch so that the pump turns off when the water level is still at least 100–150 liters – this serves as a reserve for garden pumps and prevents dry running in case of unintentional long irrigation.
In this scenario, it is also suitable to install a check valve immediately after the pump – after irrigation ends, the hose does not drain and the pump immediately starts pumping on the next activation without the need to refill the hose.
Frequently asked questions (FAQ)
Can I connect the UNILIFT KP without a float switch and let it run continuously?
This is technically possible – the pump is connected directly to the power supply without a float and runs continuously. However, it is risky. If the water level drops below the suction port, the pump will start running dry. The mechanical seal of the motor (so-called gasket) is cooled and lubricated by the pumped water – without it, it overheats and is destroyed within a few minutes. Result: a burnt motor, requiring repair or replacement. Always use a float switch or water level sensors.
The pump is running, but water is not flowing out – what is wrong?
The most common causes are: a clogged suction strainer, an air pocket in the hose, a kinked or bent hose, or an excessive head (the water level is too deep below the discharge point). Check the strainer, unroll the hose, and verify the discharge height. More solutions can be found in the article Grundfos pump not pumping or making noise – causes and solutions.
What extension cable should I use if the standard length is not enough?
For the KP 150 (power 450 W), use an extension cable with a cross-section of at least 1.5 mm² for lengths up to 20 meters. For longer distances or for the KP 250 (power 750 W), use 2.5 mm². The cable must have at least IP44 protection, cable connections must be in a dry environment and in IP65 boxes. Never use thin household extension cords.
Do I need an electrician to connect the UNILIFT KP?
If the outlet into which you are plugging the pump already has a 30 mA FI protection and is properly grounded, a plug-in connection can be done by yourself. If the outlet does not have FI protection or if it is necessary to extend the electrical installation in the basement, leave the work to an electrician – work on fixed electrical installations may only be performed by a person with electrical qualifications according to Decree 508/2009 Coll.
Can I use the UNILIFT pump in winter outside in a tank that may freeze?
No. UNILIFT pumps are not designed for operation in frozen water or in environments where the pump body may freeze. Water expands when frozen and will crack the pump body. In winter, clean the pump, flush it with clean water, and store it in a frost-free environment. If the tank is outdoors, either drain it before winter or remove the pump.
The UNILIFT pump keeps running even after the water has been pumped out – what happened?
The problem is most likely with the float switch. It may have become stuck on the wall of the pit, on the hose, or its weight has shifted. Check that the float moves freely. Another possibility: water is still flowing in faster than the pump can pump it out – in this case, the pump is working correctly, but the inflow is stronger than the pump capacity. If this happens during a flood or high groundwater level, it is a normal situation and the pump is simply maintaining a stable water level.
Conclusion – a few words before starting
The installation of the Grundfos UNILIFT pump is not rocket science, but it requires attention to a few key points: correct mechanical connection with a check valve, a rope instead of a cable for lowering the pump, a functional float switch, and absolutely a 30 mA FI protection on the electrical circuit. These four items are the difference between a pump that reliably lasts for decades and a pump that burns out or injures someone during the first failure.
If you were deciding between the KP 150 and KP 250 models while reading, a simple rule is: for a standard basement or garden tank up to 5,000 liters, the GRUNDFOS UNILIFT KP 150 A1 is sufficient. For larger volumes, deeper pits, or heads over 5 meters, go for the GRUNDFOS UNILIFT KP 250 A1 with a 10-meter cable. For more information on selecting the right model according to performance and parameters, see the articles How to choose the right Grundfos circulation pump for heating and What Grundfos pump power do I need for my home, where you will also find practical calculation methods and tables for different types of buildings.
Do you have a question about this topic?
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