Step-by-step installation of a solar pump unit

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Installation of a Solar Circulation Unit Step by Step

The installation of a solar circulation unit may seem simple at first glance – after all, you "just" hang the compact unit on the wall and connect the pipes, right? In practice, however, it looks different. After years of field experience, I know that it is precisely here that the most errors occur, which then lead to performance losses, air in the piping, operational faults, or unnecessary service visits. This article will give you a truly complete guide – from planning through mechanical installation, hydraulic connection, system filling, electrical connection, to the first start-up and regulator setup.

If you are still in the selection phase and do not yet know which unit to buy, I recommend reading the article How to choose a control unit for a solar system or Difference between a solar circulation unit and a separate controller in the Knowledge Center. Here I assume that you have already selected the correct unit and we can proceed with the installation.

What is a solar circulation unit and what components does it contain

A solar circulation unit (sometimes also called a solar station or solar station) is a compact block that integrates all the components necessary for the operation of the primary circuit of a solar system into one unit. You will find the following in it:

Circulation pump – usually an EC or standard wet-rotor pump, in ECO versions with a permanent magnet and very low power consumption (e.g. 3–45 W)
Ball valves with drain – on each side (flow/return), allowing the unit to be isolated without draining the entire system
Check valve – prevents night thermosiphon circulation, when the collectors would cool the storage tank
Manual or automatic air vent – for air removal from the circuit
Thermometer (circuit temperature) – sometimes combined with a pressure gauge
Flow meter – mechanical rotameter or electronic flow meter
Safety assembly – integrated in some models (pressure relief valve, manometer, expansion vessel)
Controller / control electronics – either built-in directly in the unit or external (depending on the model)

An example of a compact station with built-in electronics is the Solar Circulation Control Unit ZPS 18e - 01 ECO, which has the controller integrated directly in the unit body and a pump with an EC motor with a power consumption of up to 45 W. On the other hand, the Solar Circulation Unit ZP2-12 ECO is a mechanical unit without a built-in controller – you then add an external controller, for example, the Euroster 813 Solar.

Preparation before installation – this should not be underestimated

Experience from practice clearly shows that most problems do not arise during the installation itself, but due to poor preparation. Before you even unpack the unit, check the following points:

Checking the base and installation location

A solar circulation unit is typically installed in a technical room – boiler room, laundry room, or another heated room. The ambient temperature should not drop below 0 °C even in winter (the unit is not frost-resistant). The wall must be able to support the weight of the unit including the fluid in the circuit – a standard compact unit with a pump weighs 4–9 kg, and when filled with solar fluid, it can be heavier. Check whether the wall is brick/concrete (mounting into drywall without framing is not recommended).

The unit is always mounted as close as possible to the storage tank – every unnecessary meter of piping means heat losses, higher pressure loss, and longer start-up time. The ideal distance from the storage tank is up to 1–2 meters.

Height of installation

Here is a practical rule: manual valves and the air vent must be operated comfortably. The center of the unit should be placed at a height of 1.2–1.5 m from the floor. If the air vent is on top of the unit (which is common), it should not be too high to reach. At the same time, make sure there is enough space under the unit for the drain hoses when you fill or drain the system.

Tools and materials you will need

Drill, impact driver, bits and drill bits (8–10 mm for concrete)
Torque wrench or combination wrench (most commonly 24, 27, 30 mm for solar fastening)
Sealing materials – solar thread sealing (PTFE tape is not sufficient for temperatures above 100 °C, use special solar sealing or graphite rope)
Solar antifreeze (a mixture of propylene glycol and water, usually 40–50 % glycol)
Filling pump (manual or electric) for filling the system
Bucket and hoses for venting and draining
Multimeter for checking the electrical part
Thermal insulation cover for the unit (if not included in the packaging, purchase separately)

Step 1: Mechanical installation – mounting the unit on the wall

The unit is delivered with a bracket or direct mounting hardware. Procedure:

Place the bracket (or a cardboard template from the packaging) on the wall and clearly mark the drilling positions. Use a spirit level – a tilted unit is an aesthetic problem, but also a functional one (the air vent may not work properly).
Drill the holes, insert expansion anchors (minimum M8, I recommend M10 in concrete).
Secure the bracket with screws and washers. Hold the bracket by hand – it must be firm without movement.
Suspend the unit on the bracket. On some models, it is necessary to first install the connections and then hang the unit – read the installation instructions for the specific product.

Note from practice: the Solar pump unit ALEX HX10 for MiniSOL control includes a mounting bracket in the delivery, which also allows for the installation of additional accessories (expansion tank, safety group). Always check the contents of the package before drilling.

Step 2: Hydraulic connection – pipe and seals

This is the most error-prone step. The solar primary circuit operates at temperatures up to 120–150 °C (and even higher in stagnation) and at a pressure of 3–6 bar. Standard plumbing materials are unsuitable – especially rubber seals degrade at such temperatures, and soft soldering on copper may be problematic at extreme temperatures.

Pipe selection

For the solar primary circuit, use:

Copper – the ideal choice, connected using hard soldering (brass fittings). Diameter is usually DN 15 (3/4") for small systems up to 4 collectors, DN 18 or DN 22 for larger systems.
Stainless steel flexible pipe (corrugated) – used for pipe runs through walls (from collector to boiler room), resistant to corrosion and structural movement.
Solar hose – for short connections between individual devices in the boiler room, must be explicitly marked as solar (resistance up to at least 180 °C).

Do not use standard heating hoses (e.g. PEX or EPDM for central heating) in the solar circuit – they will be destroyed during stagnation.

Where is FLOW and where is RETURN

On each pump unit, the side for outlet (flow – hot fluid from the collector) and inlet (return – cooler fluid returning to the collector) is clearly marked. This must be followed – if connected in reverse, the pump runs "against itself" and the check valve prevents flow.

Practical tip: on most units, the FLOW side is equipped with a thermometer with a higher value. If you are unsure, follow the direction of the pump rotation and the arrows on the valves.

Procedure for connecting the pipe

Put the pipe fittings on the unit threads BEFORE mounting on the wall (this is not possible afterwards).
Temporarily plug the unit threads and install the pipe from the collectors through the ceiling/wall. Insulate the pipe – at minimum 19 mm rubber insulation resistant to UV radiation (outside) and heat (up to 150 °C).
Cut the pipe from the collectors to the exact length and fit the fittings on both ends.
Insert the seals – flat solar seals made of EPDM or glycol-resistant teflon. NEVER forget the seals.
Screw the fittings by hand, then tighten with a wrench (usually torque 25–35 Nm, not more – brass fittings can be damaged by over-tightening).
Connect the pipe to the solar side of the storage tank (inlet and outlet of the heat exchanger) in the same way.

Safety assembly and expansion tank

If your pump unit does not have an integrated safety group (many compact units include it), you must install it externally. At minimum, you must have:

Pressure relief valve set to max. 6 bar (or according to the project) – installed as close as possible to the collector, never after a ball valve
Expansion tank – sized for the volume of the solar fluid in the system plus the volume generated during stagnation (vapors). A common mistake I repeatedly see: too small an expansion tank = pressure relief valve discharges every sunny day
Pressure gauge – for monitoring the pressure in the system

Step 3: Installation of temperature sensors

The solar system controller operates with at least two temperature sensors. Their correct placement is crucial for the system's function – a poorly placed sensor can cause the system to not start at all, or on the contrary, to run unnecessarily.

Collector sensor (T1)

This sensor measures the temperature of the absorber or the collector's outlet pipe. It is installed in a well, which is either directly on the collector (the best option – directly on the absorber), or on the outlet pipe just behind the collector (within 30–50 cm from the collector). The sensor MUST NOT be placed in a shaded area or too far from the collector – every meter of pipe here means a temperature difference and a slower system response.

Practical mistake from practice: a customer had the collector sensor installed inside the boiler room (where the technician considered it more convenient to access). The pump started with a 40-minute delay, because the fluid had to first reach the boiler room before the sensor registered the temperature change. Moving the sensor to the roof (directly at the collector's outlet) immediately solved the problem.

Storage tank sensor (T2)

This sensor measures the temperature in the storage tank, usually in the lower third (where the water is the coldest – this is the target point for heating). The sensor is installed in a well in the tank, which most modern tanks have already prepared. If the well is missing, the sensor can be attached to the tank's outer surface with a thermal insulation cover – but this will reduce the accuracy of the measurement.

Optionally: sensor T3 (second tank, collector flow)

In two-tank systems or in systems with multiple circuits (e.g., pool + DHW), a third sensor is added. It is important to check how many sensor inputs your controller supports. For example, Euroster 813 Solar works with two sensors (collector + tank), which is sufficient for a standard single-circuit system.

Step 4: Electrical connection of the controller and pump

This is work for a person with electrical education or at least with electrical qualifications according to the regulation. In case of doubts, it is better to leave the electrical part to an electrician.

Controller power supply

Standard solar controllers and pump units are powered from the grid 230 V / 50 Hz. The power source must be protected by at least a 6A fuse (a separate circuit is ideal). A cable with grounding must be led to the distribution board (minimum 3 × 1.5 mm²). A double-pole circuit breaker should be installed near the unit for service disconnection.

Pump connection

If the pump is part of a compact unit (ZPS 18e, ZP2-12 and others), it is usually wired directly to the controller. If the pump is separate, the pump output on the controller (marked PUMP or SOLAR PUMP) is connected with a cable of at least 3 × 0.75 mm² directly to the pump's terminal block.

Sensor connection

Temperature sensors (NTC or Pt1000, depending on the controller) are connected with a two-wire cable, usually included in the controller's packaging. A sensor cable length of up to 20–30 m is not a problem – it is a low-power signal (resistance), not a high-power one. For longer runs (over 30 m), use a shielded cable to eliminate interference.

Watch out for polarity: many NTC sensors are symmetrical (polarity does not matter), but some Pt1000 sensors show negative temperatures when incorrectly connected. Always check the manual.

Optional auxiliary inputs and outputs

Modern controllers (e.g., ZPS 18e - 01 ECO) may have additional inputs and outputs – for example, a relay for a second pump, an input for a pool thermometer, an output for a signal lamp, etc. Connect these according to the specific wiring diagram in the manual – the diagrams are usually clear and well-commented.

Step 5: Filling the system with solar fluid

Filling is a step that requires enough time and calm. Rushed filling without proper air venting will cause problems during operation (air blockages, pump noise, insufficient flow).

Preparation of solar fluid

Use only mixtures of propylene glycol (non-toxic, unlike ethylene glycol) and demineralized water. The standard mixing ratio for Slovakia is 40 % glycol and 60 % water – this ensures protection down to -25 °C. In more northern or mountainous locations, increase to 50 % glycol (protection down to -35 °C). Never use car antifreeze or other liquids – these contain corrosion inhibitors unsuitable for solar systems and degrade seals.

Filling procedure

Close the safety valve temporarily with a cap (only during filling, then remove the cap!).
Attach a filling pump to the drain screw (usually on the RETURN side of the unit).
Attach a hose to the other end of the circuit (output) to vent air into a container.
Start pumping the fluid. Watch until the fluid starts flowing from the vent hose without air bubbles.
Open the manual air vent on the pump unit – release the air, then close it again.
Pressurize the system to operating pressure – usually 1.5–2.5 bar in the cold state (depends on the system height: height in meters / 10 + 0.5 bar minimum pressure).
Check all connections – is there any visible leakage? Tighten all screws (but do not over-tighten).

Leak test

After filling, let the system remain under pressure for at least 30 minutes. The pressure should remain stable (or slightly drop – due to air absorption into the seals, which is normal in the first 1–2 hours). If the pressure drops quickly, look for a leak. Typical places: connections on the unit, connections on the tank, wall/ceiling penetrations.

Step 6: Electrical startup and setting up the controller

After mechanical and hydraulic completion and after filling the system, it is time to start up the electronics. Before turning on the power, double-check the following:

Are the sensors correctly installed and connected?
Is the pump connected to the correct output of the controller?
Are the ball valves on the unit open?
Is the system pressurized to the correct pressure?

First startup

Turn on the power. The controller will initialize and display the current temperatures from the sensors. Check whether the temperatures make sense – the collector sensor should display a temperature close to the ambient temperature (if it is night or cloudy) or higher (if the sun is shining). The storage tank sensor should correspond to the actual water temperature in the tank.

If the collector temperature is significantly lower than the tank's (e.g., at night), the pump should not be running – this is the correct state. If the pump is running despite this, check the sensors to ensure they are not mixed up.

Setting up the differential thermostat – key parameters

The controller starts the pump based on the temperature difference between the collector (T1) and the storage tank (T2). Typical settings for a standard system:

ΔT for turning on (Ton): 5–8 K – the pump starts when the collector is 5–8 °C warmer than the tank
ΔT for turning off (Toff): 3–4 K – the pump stops when the difference drops to 3–4 °C
Maximum tank temperature (Tmax): 60–70 °C – protection of the tank against overheating
Night cooling function (Cooling): turned off for standard installations, turn on only in case of excessive overheating

For more information on setting up the controller, see the article How to set up a solar system controller for maximum efficiency in the Knowledge Center.

Setting up the pump flow

The flow in the primary circuit is adjusted according to the collector area. Approximate values: 40–60 liters per hour and m² of absorber area for Low-flow systems, 60–80 l/h·m² for High-flow. For a standard system with 2–4 flat collectors (4–10 m²), a typical flow rate is 150–400 l/h.

You can adjust the flow using a mechanical regulating valve on the flow meter section of the unit – follow the scale on the rotameter. If you have an electronic flow meter (such as the Electronic flow meter for GH 26), you can read the value directly in liters per minute or hour on the controller display. Learn more about how the flow meter works in the article Electronic flow meter in a solar system – what it is used for and how to connect it.

Step 7: Thermal insulation, final check, and documentation

Thermal insulation of connections and the unit

After startup and verifying the system's function, insulate all pipe connections and the pump unit itself. Most units come with a thermal insulation cover (housing). If not, you need to purchase it separately or insulate the unit with custom-cut rubber insulation. An uninsulated pipe and unit can lose 10–30 % of the collected energy even in the boiler room – this is nonsense that you can easily avoid.

Final check after the first day of operation

Check the system pressure – after the first heating and cooling cycle, it should remain stable. If it has dropped, the system may have minor leaks or an undersized expansion tank.
Expansion tank: after the first day of operation (when the system has gone through a heating and cooling cycle), bleed the air again.
Check the flow meter – the flow should remain stable.
Test the controller's response: cover the collector with cardboard or wait for cloud cover and observe whether the controller stops the pump correctly.

Installation documentation

Prepare a simple installation documentation: a photo of the wiring, a diagram with the dimensions and location of the sensors, a protocol of the first startup (date, pressure, flow, controller settings, type and concentration of the fluid). This documentation will be useful for service interventions and is also part of the inspection documentation when selling the property.

Common installation errors – what I have seen in practice

Over the years of work in this field, I have seen recurring errors. Here are the ones that occur most frequently:

Swapped sensors: T1 (collector) and T2 (tank) are mixed up → the controller starts the pump at night and stops it during the day
Undersized expansion tank: the safety valve discharges fluid every sunny day – the system loses glycol and gradually corrodes
Missing or incorrectly oriented check valve: night thermosiphon circulation cools the tank by 5–15 °C during the night
Rubber seals instead of solar ones: after 1–2 seasons, leaks appear at the connections
Insufficient air bleeding: the pump is noisy, the flow fluctuates, and the temperatures on the controller are irregular
Collector sensor too far from the collector: long response times, the system does not optimally use solar energy
Uninsulated unit and connections in the boiler room: unnecessary heat losses reduce the system's performance

Special case: two-tank systems and multi-loop systems

The standard single-tank system (collector → hot water tank) is described in this article. In practice, we also encounter systems where solar collectors supply two tanks (hot water + buffer tank for heating) or where a swimming pool heat exchanger is connected in parallel. The same procedure applies with the following additions:

The controller must support priority tank control (more in the article What controller do I need for solar collectors – selection based on the number of collectors and tanks)
Each branch requires precise flow balancing (regulating valves or a distributor with flow meters)
Each tank needs its own temperature sensor
The safety assembly must be sized for the maximum power of all collectors in stagnation

Maintenance after installation – what not to forget

Solar pump units are relatively low-maintenance devices, but a few checks once a year (ideally in spring before the season) are essential:

Check the pressure in the cold state – it should be 1.5–2 bar. If it is lower, add fluid.
Check the pH and glycol concentration – after 3–5 years, the fluid needs to be replaced or inhibitors added
Bleed the system
Visually check the safety valve (is it not clogged or damaged?)
Check the filter (if it is part of the system)

More detailed information can be found in the article Maintenance and servicing of a solar pump unit and in the article Common faults of solar controllers and pump units in case of problems.

Most frequently asked questions (FAQ)

Can I replace the solar pump unit myself, without an electrician?

You can basically do the hydraulic part (mechanical installation, pipe connection, filling) yourself if you are skilled. The electrical part – connecting to 230 V – should be handled by an electrician with the appropriate qualifications. Otherwise, you expose yourself to the risk of electric shock and the insurance may not cover the damage in case of an accident. Moreover, in many cases, the manufacturer requires professional installation as a condition for the warranty.

How long does it take to install a solar pump unit?

An experienced technician can replace or install a compact pump unit, including filling and initial setup, in 3–5 hours. Installing an entire new system (including pipe routing) is a different matter – it can take 1–2 working days depending on the scope. If new electrical work is required (a new circuit breaker), add the electrician's work as well.

What is the best solar fluid and where to buy it?

Always use a fluid based on propylene glycol (not ethylene glycol!) with corrosion inhibitors designed for solar systems. Mix it with demineralized water – regular tap water contains calcium, which forms limescale in the tank heat exchanger after repeated heating and reduces performance. A 40 % glycol concentration is sufficient for most locations in Slovakia (protection down to –25 °C). In the mountains or in the north, use 50 % (protection down to –35 °C).

What to do if the pump runs after installation, but the tank does not heat up?

The first thing: check whether the flow actually passes through the system (the rotameter should be rotating). If not, the system is likely blocked by air - bleed it. If the flow is present, check the connection of the tank's primary circuit - whether flow and return are connected to the correct ports of the tank's heat exchanger. Another possibility: the sensors are swapped and the pump stops as soon as the tank starts receiving heat. Read the temperatures on the regulator display and compare them with the actual values on the sensors.

What is the difference between ECO and standard units in terms of installation?

From the perspective of the installation itself, the procedure is the same. The difference lies in the electrical part - ECO units with an EC motor (e.g. ZP2-12 ECO) have a pump controlled by a PWM signal or a 0–10 V signal from the regulator. This means that when connecting, it is necessary to additionally connect the pump control cable to the correct output of the regulator. If you are used to standard pumps with simple relay switching, pay special attention to this step. More about the differences can be found in the article Solar pump unit ECO vs. standard - what is the difference and when is it worth it.

Can I add an electronic flow meter to an existing pump unit later?

In most cases yes, but it depends on the unit model. Some units (e.g. GH 26 and compatible) have a directly predefined input for an electronic flow meter - for example, the Electronic flow meter for GH 26 is an add-on that can be installed without further modifications. In other units, it is mechanically more complicated and it may be simpler to replace the entire unit with a version that has a flow meter as standard. Check compatibility with the seller before purchase.

Conclusion: investment in proper installation pays off

The solar pump unit is the heart of the entire primary circuit. Even the best collector or premium tank will not guarantee performance if the unit is poorly installed, poorly set up or improperly filled. Most of the problems I have solved over the years in practice originated precisely in the installation details - poor seals, air in the circuit, swapped sensors, too small expansion tank. Spend enough time and calm on the installation, do not forget about thermal insulation and documentation, and the system will reliably serve you for 20 or more years with minimal maintenance costs.

If you are looking for suitable components, in the category control units you will find a complete range of solar pump units and controllers - from simple

Do you have a question about this topic?

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