Maintenance and service of solar system – what to check every year

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System maintenance and service – what to check every year

A solar water heating system is an investment that pays back over fifteen, twenty, sometimes even thirty years with proper care. I have, however, seen many installations where the owner monitored the system with enthusiasm for the first two to three years, then got used to the fact that hot water "just flows", and gradually stopped checking anything. The result? Degraded fluid, a jammed pump, a leaking connection on the collector, and eventually a frozen pipe during frost – because the mixture had stopped circulating instead of flowing. All of this can be easily avoided with an annual inspection, which doesn't require a specialist with a university degree, but rather a systematic approach, basic tools, and a list of things to check.

This article is exactly such a list – expanded with explanations of why to check these things, what to look for, what values are normal, and when to call a professional or order a spare part. If you are interested in how the entire system works from the ground up, I recommend reading the article How to choose a solar water heating system for a family home and Sensors and control of a solar system – how they work and when to replace them first.

Why regular maintenance is necessary – not just recommended

A solar thermal system operates with temperatures that surprise the average user. In summer, the temperature of the solar fluid in the collector can easily reach 150–180 °C during stagnation (when the tank cannot absorb heat and the pump stops). Such extreme conditions degrade the inhibitors in the solar medium much faster than most manufacturers indicate in their catalogs. The result is the degradation of the glycol mixture, the formation of acid, and corrosion of internal surfaces of the heat exchanger, pipes, and circulation pump.

In addition, the solar system operates in an open temperature cycle – in winter, it can be -20 °C outside, while in summer the collector heats up to higher values. This thermal expansion and contraction stresses all connections, seals, insulation, and collector mounting. Micro-cracks that are invisible in the first year can cause fluid or air leaks after five years without inspection.

The safety expansion tank must always function properly – if the membrane loses air or the membrane bursts, the system will start "spitting" fluid out through the safety valve with every heating cycle. I have often seen customers who noticed a wet spot under the pump unit and couldn't figure out where it came from. The answer was almost always the same: a worn-out expansion tank and a valve that regularly opens.

The advantage of an annual inspection is therefore twofold: you prevent expensive failures and at the same time keep the system performing efficiently. A neglected system can lose 20–40 % of its annual heat gain, and the owner may not even notice it – the tank still heats up, just slower and for a shorter time than in the first years.

Spring inspection – the basis of annual maintenance

The ideal timing for the main annual inspection is spring – specifically April or the beginning of May. The system has just survived the winter, any frost damage is fresh, and at the same time, you have the most powerful months ahead, when you want everything to be in perfect condition. The following points are described in the order I usually go through them during a service visit.

1. Visual inspection of the roof-mounted collectors

The solar collector is exposed to weather conditions all year round, and this is exactly where most problems begin. During the spring inspection, I check the following:

Condition of the glass cover: Cracks, hail damage, darkening (indications of moisture inside the collector). A small crack at the edge may last a year without problems, but it allows moisture to enter, which then corrodes the absorber and reduces performance.
Sealing of the frame: Silicone or EPDM sealing around the glass ages and shrinks. If you see that the sealing is cracked or detached from the frame, it needs to be replaced before water enters the entire insulation space.
Mounting of the collector to the supporting structure: Check all screws, nuts, and consoles. Wind load during winter can loosen connections. If the collector moves slightly when you press it with your hand, it is a serious safety issue – collectors weigh 30–50 kg and can cause serious injuries if they fall.
Absorber (through the glass): A clean absorber has a dark, uniform blue or black color. If you see light spots, dots, or gray areas, it may indicate corrosion caused by moisture or degraded fluid.
Dirty glass: Bird droppings, moss, lichens, and dust can reduce the glass transmission by 5–15 %. Cleaning is simple – just clean water and a soft cloth, or a telescopic mop. Do not use aggressive cleaning agents or pressure washing – they can damage the sealing.

With the flat frame solar collector IVAR.SOLAR 210 M5 with dimensions 1230×1696×86 mm, also pay attention to the fact that the outlet flanges and hose connections are on the back side of the collector – check their accessibility and visual condition, and seal them if you see traces of salted glycol mixture (white or brown deposits around the joint).

2. Inspection of the solar pipe and its insulation

The pipe is the most common source of heat loss and also the place where leaks are hidden and hard to see. I inspect the following:

Insulation of the external pipe: UV radiation damages rubber insulation – every year, check whether the insulation is cracked, hard or disintegrating. If the insulation is missing on a section longer than 20–30 cm, the heat loss at this point is significant, and in winter, freezing can occur.
Signs of leaks: Dried white or yellow-brown deposits on the pipe, signs of moisture, discolouration on the wall – these are indications that a joint is leaking or "sweating". In such cases, remove the insulation at that location and inspect the joint.
Condition of the stainless steel pipe: If you have installed stainless steel pipe with rubber insulation and a diameter of 2×16 mm, check whether the rubber insulation adheres along the entire length and is not interrupted. These hoses are significantly more durable than standard copper or plastic ones, but their insulation also degrades over time due to UV exposure.
Pipe fastening: Clamps and mounting brackets should be secure. A loose pipe vibrates during pump operation, which causes material fatigue at the connection points.

3. Condition and quality of the solar fluid

This is perhaps the most important point of the entire inspection and also the one most often neglected by owners. Solar fluid – a mixture of water and propylene glycol with inhibitors – has a lifespan of 3–6 years. After this period, the inhibitors lose their effectiveness, pH drops (the fluid becomes acidic), and internal corrosion of the system begins.

How to check this without a lab? A basic set includes a refractometer and pH test strips:

Refractometer: Measure the glycol concentration. The correct value for Slovak conditions is protection down to -28 °C to -35 °C, which corresponds to a concentration of approximately 40–50 % glycol. If it shows a lower value, the system is poorly protected against frost.
pH strips: The correct pH value is 7–9. If the pH is lower than 7 (acidic fluid), replace the fluid immediately. Acidic solar fluid corrodes copper, brass and aluminium over months.
Fluid colour: Fresh solar fluid is light, sometimes pinkish (depending on the manufacturer). Dark, brown to black fluid indicates degradation and corrosion. Many systems where I have seen such fluid also had a damaged tank heat exchanger.
Smell: Degraded fluid has a sour, sharp smell. Fresh fluid smells neutral or slightly sweet.

Replacing the solar fluid is a job that takes 2–4 hours for two people. The old fluid is drained, the system is flushed with clean water, and then filled with a new mixture. This is also an ideal opportunity to check the system's air venting.

4. Pump unit – the heart of the system

When looking at the solar pump unit IVAR.SOLAR K with regulation IVAR.SOLAR IMTDC, I check several things at once. This unit integrates a circulation pump, regulator, flow meter, safety valve and other components – each of them requires attention.

Pump – noise: Solar pumps should operate quietly or with a gentle hum. Clicking, screeching or pulsing sounds indicate air in the system, worn bearings or a problem with the flow meter.
Flow meter: Check whether the float is at the correct level and moves when the pump power changes. A frozen or stuck float may indicate air or impurities in the fluid.
Manometer: The operating pressure should be in the range of 1.5–3 bar (depending on the height of the collector above the pump unit and the system's filling pressure). If the pressure is zero or below 0.5 bar, the system has either lost fluid or has a problem with the expansion tank. If the pressure is higher than 3.5 bar with cold fluid, the expansion tank is not functioning properly.
Safety valve: The valve should have a clean discharge pipe. If you see dried traces of glycol fluid around the outlet, the valve has opened in the past – this is a reason for further investigation.
Ball valves: Check that all service valves are in the correct position (fully open). Turn and return them to position – long-term fixation of a valve in one position can lead to jamming.
Seals and joints on the unit: Place your hand on the joints and press – any moisture indicates leaks that need to be addressed immediately.

5. Expansion tank – an underestimated component

The expansion tank compensates for the expansion of the fluid when heated. It consists of a steel tank divided by a membrane – one side is filled with nitrogen under pressure, the other absorbs fluid from the system. The membrane ages and cracks, nitrogen escapes and the tank stops performing its function.

Inspection is simple: disconnect the fluid from the system (close the valve), and measure the pressure from the nitrogen side valve (similar to a bicycle valve). The correct value for most solar systems is a pre-charge pressure of 1.0–1.5 bar. If it shows zero or an extremely low value, liquid is likely penetrating through the membrane and the tank must be replaced.

6. Temperature Sensor Check

Solar system regulation depends entirely on the accuracy of temperature sensors. A correct controller compares the temperature of the collector and the temperature in the storage tank – if the difference is greater than the set value (typically 6–10 °C), the pump is activated. If the sensors show incorrect values, the entire system operates inefficiently or not at all.

There is a simple test: in the early morning, compare the temperature of the collector according to the controller with the actual ambient temperature. A deviation of ±3 °C is acceptable. A larger deviation indicates a problem – either a corroded contact on the sensor, a damaged cable, or the sensor itself.

For inspection and possible replacement, ideal sensors are those that fit directly into the tank’s immersion well – for example, a temperature sensor for immersion with resistance up to 180 °C and a 2 m cable, which can handle solar stagnation temperatures without degradation. If the storage tank is located further away and the cable is not long enough, a suitable option is also a version with a 4-meter PVC cable with a range up to 95 °C – this is suitable for the tank sensor (not for the collector, where a higher temperature range is required).

To check the sensors, proceed as follows:

Visually inspect the cable along its entire length – bends, pass-throughs, terminal blocks. Cracked insulation or moisture in the terminal block causes parasitic resistances that alter the measured temperature.
Check that the sensor is firmly seated in the immersion well. A retracted sensor measures ambient air temperature, not the liquid.
If in doubt, measure the resistance of the sensor (NTC 10kΩ or PT1000 depending on the type) and compare it with the manufacturer’s table.

Summer Check – Stagnation and Overheating

In July and August, when the tank is full and the sun is shining at full strength, the solar system enters so-called stagnation – the pump stops because the tank cannot absorb more heat, and the collector heats up to extreme temperatures. In flat collectors, this is typically 150–190 °C, while in tubular collectors it can be even higher.

During this period, the solar fluid evaporates in the collector, the vapor moves through the pipe and returns. This cycle is normal, but it stresses the safety valve, expansion system, and the fluid itself. After each summer, I recommend:

Checking the discharge of the safety valve – traces of fluid indicate that the pressure in the system exceeded the set value (typically 6 bar).
Checking the color and pH of the fluid – summer degrades the fluid faster than winter.
Checking the hoses around the pump unit – rubber seals and hoses age with repeated heating and cooling.

Autumn Preparation for Winter

October is the second mandatory inspection period. Before the first frosts, you want to be sure that the system is properly filled, the anti-freeze protection is sufficient, and the pump will start the fluid circulation if freezing threatens.

Fall maintenance steps:

Measuring antifreeze protection: Use a refractometer to measure the freezing point of the fluid. For Slovakia, I recommend protection down to at least -28 °C, up to -35 °C in mountainous areas. If the value does not meet the minimum requirement, add glycol concentrate or replace the entire fluid.
Pump test: Start the pump manually via the regulator menu. It should start within 10–20 seconds. If it does not start or runs irregularly, refer to the article Stuck or weak solar pump – causes and solutions.
Pressure topping up: If the manometer shows less than 1.5 bar with cold fluid, top up the pressure via the filling valve. The system must not be started below 1 bar – you risk pump cavitation and air in the system.
Depressurization: Always bleed the system through the bleed valves when adding fluid – on the collector (if accessible) and on the pump unit.

Hot water tank – anode and heat exchanger inspection

The hot water tank is a part of the solar system that is often neglected during service checks. Yet, it is precisely here that internal surfaces are most at risk of corrosion – a combination of salt water, high temperatures, and insufficient protection can damage stainless steel or enameled walls.

The most important component is the magnesium anode. This magnesium rod sacrifices itself instead of the tank walls – it corrodes, not the tank. The anode's lifespan is typically 2–5 years, depending on water hardness and temperature. Inspection procedure:

Turn off the tank and drain a small amount of water to confirm pressure.
Unscrew the anode (hex head 1 ¼" or ¾").
A new anode has a diameter of 25–33 mm and a length according to the tank. If the anode is thinner than 10–12 mm or shorter by more than 50 %, replace it immediately.
Never operate the tank without an anode – the walls will start to corrode.

Check the solar heat exchanger in the tank indirectly: if the system has significantly lost performance (the tank heats more slowly than in previous years under the same weather conditions), the heat exchanger may be clogged with deposits. Flushing the heat exchanger requires disassembly and professional service.

Controller and electrical installation

The solar controller is the brain of the system. Modern controllers store statistics – kilowatt-hours of heat captured, number of pump starts, maximum temperatures reached. These data are a goldmine for problem diagnostics.

What to check on the controller:

Error messages: Check the history of error codes (if the controller has memory). Repeated sensor or pump errors indicate an emerging problem.
Differential temperature settings: Typical settings are Δt=6 °C for turning on, Δt=2–3 °C for turning off. Incorrect settings cause either too frequent switching (noise, pump wear) or unnecessarily delayed activation.
Electrical connections: Check if cable glands are tight (moisture), if terminals are not corroded, and if fuses are in good condition.
Display and buttons: If the controller shows light artifacts or does not respond, it may be condensation inside – indicating a leaky installation box.

Roof mounting structure – safety first

The load-bearing structure of the collectors must withstand not only the weight of the collectors themselves (30–50 kg each), but also snow and wind loads. In Slovak conditions, snow load in mountainous areas can be 2.5–3.0 kN/m².

Once a year – best in spring – check:

Stainless steel screws and nuts on the consoles – corrosion is a risk when using regular steel.
Roofing around pipe penetrations – moisture entering the roof structure is a time bomb.
Overall position of the collectors – whether they have changed compared to the previous season (inclination in mm per 1 m length).
Condition of the roofing material around the structure – cracks, lifted tiles.

For more information on proper placement and securing, read the article How to properly place and secure solar collectors on the roof.

When to call a professional and when you can handle it yourself

Most annual maintenance is within the ability of a resourceful homeowner who is not afraid of a ladder, basic tools, and patience. However, there are situations where it is better to call a service technician:

Replacement of the entire solar fluid (draining, flushing, filling under pressure) – requires proper equipment (filling pump, refractometer, bleeding).
Diagnosis and replacement of the solar pump – requires disassembling the pump unit and working with pressure in the system.
Replacement of the expansion tank – operation under pressure.
Any work on the roof in adverse conditions or on steep slopes over 35°.
Suspicion of corrosion in the tank heat exchanger.

On the other hand, cleaning the collectors, visual inspection, measuring pH and glycol, checking the controller, and basic seal inspection – these are tasks you can handle yourself in a few hours per year.

Service inspection records – why to keep them

I recommend keeping a simple service log – it can be a paper notebook or a spreadsheet file. Record:

Date of inspection and who performed it
Measured pH value and glycol concentration
Operating pressure with cold and hot fluid
Water tank temperature at the end of a sunny day in May and September (a good performance reference)
Any anomalies, repairs, or part replacements

These records will be useful when selling real estate (they prove care) or when claiming warranty on components – many manufacturers condition warranty on documented regular maintenance.

Typical annual maintenance costs – a realistic view

Annual maintenance of a solar system is not financially burdensome if it is regular. An approximate overview of costs for a family home with 2–4 collectors:

Solar fluid (replacement every 4–6 years): 80–150 € for the fill + labor
Water tank magnesium anode (every 3–4 years): 20–50 €
Seals and minor repairs: 10–30 € annually
Possible sensor replacement: 15–40 € per piece
Service visit by a technician (if needed): 80–150 € per hour

Overall, with thorough self-maintenance and professional service every 3–4 years, you can expect average annual costs of 50–100 €. Given an annual savings of 400–700 € on water heating (depending on the system), this is a very favorable ratio.

Most frequently asked questions about solar system maintenance

How long does solar fluid last without replacement?

The official recommendation from most manufacturers is replacement every 4–5 years. In practice, it depends on how often the system has experienced stagnation (temperatures above 150 °C) and the quality of the original fill. Basic pH and color tests can be done at home – if the pH drops below 7 or the fluid is dark, do not delay replacement even after 3 years.

Can I top up the solar fluid myself if some has leaked out?

No, without measurement. If you top up with a mixed fluid of unknown concentration, you may disrupt the frost protection. Always measure the freezing point with a refractometer and, if the concentration is low, top up with pure concentrate, not a mix. If you have lost a large amount of fluid (more than a liter), it is better to drain and refill the entire system – this ensures correct concentration and proper bleeding.

What to do if the controller shows a sensor error?

First step: check the physical connection of the sensor to the controller – ensure terminals are tightened and cables are not damaged. Second step: measure the sensor resistance with a multimeter and compare it with the manufacturer's table for the given temperature (for NTC 10kΩ, the resistance at 25 °C is 10 kΩ). If the resistance does not match or is infinite, the sensor is damaged and must be replaced. More information can be found in the article Sensors and solar system control – how they work and when to replace them.

Is it normal for the safety valve to drip slightly in summer?

No – the safety valve should be hermetically sealed except in cases of actual overpressure. If the valve drips regularly during summer heatwaves, the system is operating at too high a pressure or the expansion tank is damaged. The nitrogen pressure in the expansion tank should be checked and its volume increased if necessary. Ignoring this issue leads to rapid wear of the valve and fluid leakage.

When is it necessary to replace the collector itself?

A well-maintained collector usually lasts 20–30 years. Clear signs for replacement are: cracks in the glass layer that cannot be repaired; visible corrosion of the absorber (surface, not spot corrosion); the collector does not reach temperatures even in direct sunlight (less than 40–50 °C in summer), indicating vacuum loss (in tubular collectors) or degradation of the selective coating. In flat plate collectors, replacing the cover glass may be an economically viable alternative to a full replacement.

How can I tell if my solar system is working properly without measuring?

The simplest indicator: on a clear summer day (May–September), the storage tank (150–200 l for 3–4 people) should be heated to 55–65 °C by 14:00, assuming the system started at around 15–20 °C in the morning. If the tank does not reach even 45 °C or heating has significantly slowed compared to previous years, it is time for a thorough diagnosis – start by checking the fluid and cleaning the collectors.

Conclusion – an investment in inspection pays off

A solar system operates quietly, unobtrusively, and without daily attention. Precisely for this reason, it is easy to forget about it – and when a problem arises, it is not a cheap matter. Practical experience speaks clearly: systems that undergo a structured annual inspection perform significantly better and last longer than those where action is taken only after a visible failure occurs.

In short: two hours once a year, a pH meter, a refractometer, and a look at every connection and cable will save you hundreds of euros in breakdowns and preserve system performance for decades. If you are interested in proper pipe and pump unit sizing when planning a system, I recommend the article Dimensioning Solar Pipes and Pump Units – How to Do It, and for an overall overview of installation, the article Installing a Solar System Step by Step – from Collector to Storage Tank.

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