When to Replace the 20 Micron Replacement Insert
Why 20 microns is a key threshold in the heating system
In practice, when I meet with plumbers or building managers who ask about replacing filter inserts, I most often hear the question: "How do I know it's time to replace?" When it comes to water filtration in heating systems, the answer is not always black and white. We are talking about a technology where the precision of water cleaning directly affects the boiler's lifespan, radiator efficiency, and overall operational safety. An insert marked with 20 microns (20 µm) represents a specific category – it is not a coarse mechanical filter for large impurities, nor is it a final polishing insert. It is the "golden middle" value that captures fine sediment, iron oxides, and sand that would otherwise flood valve bodies and clog heat exchangers.
Many users mistakenly equate a 20-micron insert with a standard PP filter rated at 5 or 10 microns. The difference is significant not only in pore size but also in how the pressure drop across the filter changes. If your system is connected to a public water supply with a high content of algae and sand, 20 microns can be an ideal solution as a pre-filter before more expensive treatments. Conversely, in older systems with strong corrosion, this insert may quickly lose functionality if not replaced in time. In this article, we will look deeply beneath the surface so you understand when it's time for a replacement, how to diagnose it without disassembly, and why ignoring this step can cost you tens of euros extra in boiler repairs.
What does 20 microns actually mean?
Before we get to practical tips on replacement, we need to define what exactly "20 microns" means. A micron (µm) is one thousandth of a millimeter. For comparison, human hair has a diameter of approximately 70 to 100 microns. This means that a 20-micron insert can capture particles that are about three times thinner than a hair. This category includes:
- Sludge and fine sand: Particles that pass through 50-micron sieves but are stopped by a 20-micron one.
- Oxidation deposits: Fine particles of iron oxides (so-called "black sludge") that form due to corrosion in old pipes.
- Bacteria and biofilm: Some bacteria are about 1-5 microns in size, but their colonies and slime layers often attach to larger particles that a 20-micron filter captures and prevents from circulating.
- Seal shavings: Small fragments of rubber seals that can be released during the installation of new fittings.
This type of insert is usually made from polypropylene fibers (PP), which are interwoven to form a three-dimensional mesh. Unlike stainless steel sieves, which work on the principle of liquid passing through holes, a PP insert works on the principle of adsorption and mechanical retention. The more particles it captures, the lower the flow and the higher the pressure before the filter.
Technical indicators of the need for replacement
In a professional environment, we do not look only at a time schedule, but at real system parameters. You must replace the 20-micron insert when critical pressure or flow parameters change. Here are the specific signals I have observed over the years of practice in various buildings.
1. Pressure drop (Differential pressure)
The most accurate indicator is the pressure difference before and after the filter. A new, clean 20-micron insert should have minimal resistance. Typically, the pressure drop (the difference between the pressure gauge before the filter and the pressure gauge after the filter) should be less than 0.1 to 0.2 bar. When the insert starts to absorb impurities, the resistance increases exponentially.
If you measure a pressure difference higher than 0.5 bar, it is a warning sign. At values of 0.8 to 1.0 bar, immediate replacement is necessary. Why? Because excessive pressure drop causes two problems. First, reduced flow in the system means the boiler does not receive enough heat, which causes frequent shutdowns for overheating protection or unstable operation. Second, increased pressure before the filter can damage the filter body itself, especially if it is plastic, or cause leaks at seals not designed for such loads.
2. Drop in heating performance
Practical example from practice: We came to a family house where the owner complained that the radiators on the upper floor were not heating. Inspection showed that the main circuit was working, but the lower floors were cold. After checking the filter, it turned out that the 20-micron insert was completely clogged with black sludge. The result was that the pump did not have enough flow to deliver hot water to the upper floors. After replacing the insert, the pressure stabilized and the system started working properly. If you notice that your heating system is reacting slowly or you need longer times to heat the rooms, check the condition of the filter.
3. Visualization and water color
Although a 20-micron insert is not designed for visual monitoring (unlike transparent vessels), when replacing it, you can see the result of your work. If after disassembly you find that the insert is black, brown or gray and light does not pass through at all, it is clear that it has fulfilled its function. However, if the insert looks relatively clean but the pressure is high, it may indicate a problem with incorrect installation or damaged sealing that allowed the insert to bypass. In this case, the insert must be replaced, as the system is not protected.
Practical scenarios and replacement frequency
One of the most common mistakes users make is setting a fixed replacement schedule, for example, "once a year." Reality is much more complex. The frequency of replacement depends on the quality of the incoming water, the condition of your system, and the type of insert. Below I present specific scenarios that I have observed in various jobs.
Scenario A: New construction and clean piping
In new construction, where new copper or plastic pipes were used and the system was thoroughly flushed before commissioning, a 20-micron insert can last up to 12 months or even longer. In this case, the insert serves more as protection against impurities from installation or small particles from the water supply pipes. If you have this type of system, it is sufficient to check the insert once every six months. If it is clean, you can leave it for several more months. For this purpose, standard filters such as Filter 5" - 1/2"F; without insert are ideal, which allow you to easily replace and check the insert.
Scenario B: Reconstruction of an old system
This is the situation where filter inserts are changed most frequently. Old electric boilers, rusty steel pipes, and aluminum radiators produce a huge amount of iron oxides. In such a system, a 20-micron insert can lose its permeability within 3 to 6 months. It often happens that after the first winter season, the insert is completely black and as hard as stone. If you allow the insert to remain in such a system for too long, you risk the dirt breaking through the insert and clogging the valve bodies or the boiler's heat exchanger. In this case, I recommend replacing the insert every 3 to 4 months, or even more frequently if the pressure drop is high.
Scenario C: System with high sand content
Another extreme is water with a high sand content, for example, from a private well or in areas with sandy soil. Even though the water is potable, it contains mineral particles that are harmful to the heating system. In such a case, a 20-micron insert functions as a very effective mechanical filter. However, you must expect that it will clog more quickly. It often happens that the insert clogs within a week. If you use this type of water, consider installing a stainless steel mesh filter as a pre-filter and a 20-micron insert as the final filtration. For this purpose, it is suitable to use Filter 5" - 3/4"F; stainless steel insert - promotion as the first stage and then a 20-micron insert.
Difference between PP insert and stainless steel mesh
It is important to distinguish between two types of filters that are often confused. A stainless steel mesh (e.g., 400 or 800 microns) and a 20-micron PP insert have different functions. A stainless steel mesh is permanent, can be washed, and is used to capture large particles (rust lumps, gravel, sand). A 20-micron PP insert is a consumable material that must be regularly replaced, as it captures fine particles that pass through the stainless steel mesh.
If your system has only a stainless steel mesh, your 20-micron requirements are not met. The fine sediment will pass through the mesh and settle in the boiler. Conversely, if you have only a 20-micron insert without a pre-filter, the insert will clog very quickly and you will have to replace it every week. The optimal solution is a combination: a stainless steel mesh as the first stage and a 20-micron PP insert as the second stage. This setup ensures that the stainless steel mesh captures large impurities and the 20-micron insert completes the cleaning process. For such solutions, it is ideal to use Filter 5" - 3/4"F; PP insert - promotion, which is specifically designed for these purposes.
Replacement procedure and preventive maintenance
The replacement of a 20-micron insert should be performed by anyone with basic technical knowledge. The procedure is simple, but safety must be observed. First, turn off the boiler and close the water supply to the system. Disconnect the pump power supply if it is separate. Then gradually loosen the filter cover. On older systems, the cover may be heavy due to deposits, so be careful not to damage the thread. Remove the old insert and check its condition. If the insert is deformed or has cracks, discard it immediately. Before inserting the new insert, clean the inside of the filter from dirt that may have accumulated at the bottom. Insert the new insert so that it seals properly on the gasket. Make sure the gasket is clean and not damaged. Close the cover and tighten it according to the manufacturer's instructions. Do not tighten too much to avoid damaging the thread, but also not too little to prevent leaks.
After installation, open the water supply again and check for leaks. If everything is in order, turn on the boiler and monitor the pressure. The pressure may be slightly higher on the first day after replacement until the system fully stabilizes. If the pressure remains high, check whether the insert is correctly mounted and not damaged.
2. Bypass diagnosis
In practice, it often happens that the pressure drop is high, yet the insert appears relatively clean. The reason may be so-called "bypass" – water bypasses the filter insert through a damaged gasket or improperly mounted cover. In the diagram below, you can see the difference between correct flow and water leakage around the insert, which leads to an unprotected system despite a low level of clogging.
4. Visual inspection of deposits (Black sludge)
In practice, it often happens that the pressure drop is still within the normal range, but the filter media has already lost its filtering capability due to so-called "blinding" or the formation of a gel-like layer on the surface of the fibres. In the diagram below, you can see the difference between a new filter media and one that is clogged only by a surface layer of black sludge (so-called "cake"), which creates a false sense of cleanliness during a visual inspection without disassembly.
Frequently asked questions (FAQ)
When exactly should I replace the 20-micron filter media?
We recommend replacing the filter media when the pressure drop exceeds 0.5 bar, or if the filter media is visually completely clogged with black sludge. In older systems, replacement may be necessary every 3 months, while in new systems, once a year is sufficient.
Can I wash and reuse the 20-micron filter media?
No. Polypropylene filter media are designed as single-use consumables. Attempts to wash them can damage the fibre structure and the filter media will lose its filtering capability. Moreover, washing does not remove all microorganisms or chemical deposits.
What is the difference between a 20-micron and a 5-micron filter media?
A 5-micron filter media filters finer particles, but has a significantly higher pressure drop and clogs more quickly. It is suitable only in cases where the water is very clean and high purity is required (e.g., for condensing boilers with sensitive components). For standard heating systems, 20 microns is the optimal choice.
Why does my filter keep clogging?
This may indicate that there are many impurities in the system that are not being removed. Check whether you have the correct pre-filter (stainless steel mesh) and whether the system is properly flushed. Also check whether there is air in the system, which can cause erosion and the formation of impurities.
Is it better to use a stainless steel mesh instead of a PP filter media?
A stainless steel mesh is durable and can be washed, but it does not have the same high filtering capacity as a PP filter media. For the best results, it is advisable to combine both: a stainless steel mesh as a pre-filter and a PP filter media as the final filter.
Conclusion: An investment in cleanliness is an investment in the health of your boiler
Replacing the 20-micron filter media is not just a routine task, but a key step in the maintenance of your heating system. Choosing the right time for replacement, understanding pressure parameters, and using quality products such as, for example, Filter 5" - 1"F; without media or other products from our range, will save you dozens of euros in boiler repairs and ensure the long life of your system. Remember that clean water is the basis of efficient heating. If you have any doubts about the condition of your filter or need help choosing the right type of filter media, do not hesitate to contact us. Together we will find a solution that meets your specific conditions.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us - we are happy to help.