common faults and clogged filters in heating
Why your heating stops: Real causes of clogging and filter faults
In practice, having spent decades on installations and servicing heating systems in both residential and industrial settings, I have learned one golden rule: if the boiler shuts down due to pressure or temperature error, 90% of the time the problem is not in the boiler itself, but in the water quality and its cleaning. A common issue we see when visiting customers is a sudden drop in heating performance, noise in the pipes, or complete circulation stoppage. Most owners immediately call the boiler technician, but the real culprit of their system often sits in a small body at the inlet of the boiler circuit.
Filtration is not just an "optional service" recommended for safety. It is a critical protective barrier. Any essential component in the system—whether it is radiators, floor heating, or heat pumps—requires clean water. Impurities naturally present in the water or formed by corrosion in old installations gradually settle. Without proper filtration, these particles disrupt hydraulic distribution, clog heat exchangers, and lead to costly repairs. This article provides a detailed analysis of how clogging occurs, what types of faults it causes, and how to properly set up maintenance to avoid expensive interventions.
Anatomy of the problem: What exactly clogs filters and systems?
When we talk about clogging, we must understand that it is not one type of dirt. Water in the heating system contains a complex mixture of substances, which are generally divided into mechanical and chemical. Mechanical impurities include sand, gravel, rust flakes, iron oxides, plastic fragments from joints, and remnants of sealing materials after installation. Chemical impurities are then calcium solids (limescale), biofilm, and colloidal substances that create sludge.
A practical example from our practice: During the replacement of an old boiler in a family house, we found that the inlet filter was completely clogged with black, greasy sludge. After disassembling the filter, it turned out to be a mixture of iron oxide and biological biofilm, which had formed due to the absence of disinfection and the long-standing stagnant water. This sludge has a viscosity that can completely block the flow, even though the filter mesh was only slightly dirty. This means that standard mechanical filtration is not enough if water treatment is not also done chemically.
An important aspect is also the size of the particles. A standard water supply pipe can contain particles ranging in size from 1 micrometer to several millimeters. If you have floor heating with thin tubes (for example, PEX-Al-PEX with an internal diameter of 16 mm), even a small particle that gets stuck in a bend can create a local flow restriction. This causes uneven heating of rooms and subsequent pipe vibrations, which is a signal to the technician that something is wrong.
In the diagram above, you can see a simple representation of water flow. On the left, you see a pipe with various sizes of impurities (corrosion, sand). When water passes through the filter, larger particles are captured, while smaller ones can pass further. However, if the filter is too dense or the dirt is sticky (sludge), clogging occurs quickly and flow drops. This is the moment when pressure problems in the system appear.
Key factors that accelerate clogging
Not every system clogs at the same speed. There are factors that dramatically accelerate this process. The first and most important factor is the age of the installation. In older systems where steel pipes were used, internal corrosion is constant. Iron oxidation creates thick layers of rust flakes, which are released and circulate in the system. These particles have a flaky shape, which means they easily settle in narrow spaces and form solid blockages.
The second factor is the quality of tap water. In some regions of Slovakia, the water is very hard, meaning it has a high content of calcium and magnesium. When heated above 60 °C, these minerals precipitate and form calcium crystals. These crystals settle on the walls of heat exchangers and filters. If you do not have softened water or an ionizer in your system, the risk of deposits is high. The third factor is incorrect installation. If the pipes in a new system are not sufficiently flushed during installation, residual particles from production, tapes, teflon, or soldering materials remain in them. These particles are released after a few operating cycles and immediately clog the filter.
The fourth factor is the lack of maintenance. Many owners think that a filter is "installed and forgotten." The opposite is true. A filter must be regularly checked and cleaned. If dirt accumulates in it, it stops performing its function and starts acting as a flow restrictor. This leads to increased pressure before the filter and decreased pressure after it, which can cause the activation of safety valves or boiler shutdown.
Difference between manual and automatic filters in practice
One of the most common questions we get from customers is: "Should I install a manual filter or an automatic one?" The answer depends on the type of system and your willingness to spend time on it. Manual filters, such as standard 5" filters, are cheap and effective, but they require regular maintenance. You have to open them, remove the insert, wash or replace it, and reassemble them. If you don't do this, the filter will clog and the system will stop working.
Automatic backwash filters are more expensive, but they offer greater convenience. They work on the principle of reverse flushing, which washes away impurities into the sewer without the need for disassembly. They are ideal for commercial buildings or homes where no one is available for maintenance. However, even automatic filters have their limits. If the water is very dirty, the backwash system can clog or fail to remove all impurities. In such cases, manual cleaning is necessary.
In our practice, we have seen cases where a customer installed an expensive automatic filter but forgot to set it to the correct backwash mode. The result was that the filter became a passive object and dirt settled inside it. Therefore, it is important not only to buy the right filter but also to understand its function and set it according to the conditions in the system.
The image illustrates the difference in maintenance between a manual and an automatic filter. A manual filter requires physical intervention, while an automatic filter cleans itself using a backwash. Both solutions have their place, but it is important to choose the one that best suits your needs and maintenance capabilities.
Types of filter inserts and their impact on filtration efficiency
One of the most important elements of a filter is the insert. In the category of filtration and water treatment, you will find two main types of inserts: PP (polypropylene) and stainless steel mesh. Each of these types has its advantages and disadvantages, which a technician should be aware of.
PP inserts (polypropylene): These inserts are made of non-woven polypropylene and have a defined microporous structure. They are ideal for removing fine impurities such as sand, silt, and corrosion particles. Their advantage is a high capacity for capturing impurities and good water permeability. The disadvantage is that they become clogged over time and must be replaced. PP inserts are available in various pore sizes, for example 5, 10, 20, 50, and 100 microns. For standard heating systems, 20-micron inserts are recommended, as they can capture most impurities without excessively restricting the flow.
Stainless steel meshes: These inserts are made of stainless steel and have a mesh structure. They are more resistant to wear and can be used multiple times. Their advantage is the possibility of reuse after cleaning. The disadvantage is a lower capacity for capturing fine impurities. Stainless steel meshes are suitable for systems where the water is relatively clean and the main goal is to remove coarse impurities such as sand and metal particles.
In practice, we have found that a combination of both types of inserts can yield the best results. For example, you can use a stainless steel mesh as the first stage to remove coarse impurities and then a PP insert to remove fine impurities. This configuration extends the life of both inserts and improves the overall filtration efficiency.
When and how often to replace the insert? A practical guide
One of the most common mistakes we see among customers is leaving the insert in the filter for too long. The insert should be replaced depending on the water quality and the frequency of system use. For standard home systems, it is recommended to replace the insert every 3 to 6 months. If the water is very dirty or the system is new, the insert should be replaced more frequently, for example every month.
How to tell when it is time to replace the insert? The simplest way is to monitor the pressure in the system. If the pressure before the filter is significantly higher than the pressure after the filter, it means that the insert is clogged. Another indicator is a drop in water flow or noise in the system. If you hear bubbling or cracking sounds in the pipes, it may indicate that the insert is clogged and the water is flowing through small openings at a high speed.
The procedure for replacing the insert is simple. First, close the valves before and after the filter. Then unscrew the body of the filter and remove the old insert. Install the new insert into the filter body and tighten it. Finally, open the valves and check for any water leaks. It is important to maintain hygiene during the replacement of the insert and not to introduce new impurities into the system.
For better control and longer system life, we recommend using high-quality inserts, such as those available in our range. For example, Filter 5" - 3/4"F; PP insert - promotion is suitable for standard home systems and offers an excellent price-to-quality ratio. If you need higher durability, you may consider Filter 5" - 3/4"F; stainless steel insert - promotion, which is suitable for systems with a higher concentration of impurities.
Real-life examples: How a clogged filter manifests in a real system
Let's talk about a specific real-life example. A customer came in with the issue that their heating system was not working in winter. The radiators were cold and the boiler kept turning off. After an inspection, we found that the filter at the boiler inlet was completely clogged with black sludge. After cleaning the filter, the system was restored and the radiators started heating up. The customer asked why this happened. The answer was a lack of maintenance and the use of poor-quality water.
Another example: A floor heating system in a new building. The customer installed a new boiler and floor heating but forgot to install a filter. After a few weeks, they started having problems with uneven heating of the rooms. After an inspection, we found that impurities from the installation had settled in the pipes. After installing a filter and cleaning the system, the problem was resolved.
These examples show that a filter is not just an optional component, but a critical element that protects your system from serious damage. If you want your system to operate reliably and for a long time, you must ensure good filtration and regular maintenance.
Hydraulic pressure difference as an indicator of clogging
A key technical parameter in diagnostics is the measurement of the pressure difference before and after the filter (delta P). For a clean filter, this difference should be minimal, usually below 0.1 bar. If the value increases above 0.2 to 0.3 bar, the filter is no longer just a passive barrier, but an active flow restrictor that forces the pump to operate under unfavorable conditions and increases the risk of cavitation.
Impact of sludge on the hydraulic curve of the system
When a sticky sludge (biofilm mixed with iron oxides) forms in the water, the problem is not only in the mechanical clogging of the mesh. The sludge also settles on the walls of the pipes and radiators, reducing their internal diameter. This causes a non-linear increase in system resistance – at the same pump performance, the water flow will decrease exponentially. As a result, the boiler "sees" the system as too high resistance, which leads to its constant shutdown due to overflow or high temperature difference.
Frequently asked questions and answers (FAQ)
Why does my filter keep clogging even after I clean it?
If the filter clogs very quickly, it may indicate that there are too many impurities in your system. We recommend checking the water quality and considering the installation of a stronger filter or a dual filtration system. Also, check whether there is a source of impurities in the system, such as an old radiator or a dirty pipe.
Can I use a 10-micron insert instead of a 20-micron one?
Yes, you can, but you must consider that an insert with a smaller pore size will create higher resistance to water flow. This can lead to a drop in flow and increased pressure in the system. A 20-micron insert is usually sufficient for standard home systems. If you have very clean water, you can use a 10-micron insert.
How can I tell if the filter is clogged?
The best way is to monitor the pressure in the system. If the pressure before the filter is significantly higher than the pressure after the filter, it means the filter is clogged. You can also monitor the water flow and noise in the system. If the flow is low or you hear noise, the filter may be clogged.
Is it possible to flush the filter without disassembling it?
Yes, if you have an automatic filter with a backwash function, you can flush it without disassembling. If you have a manual filter, you need to disassemble it and clean or replace the insert. Some manual filters also have a flushing option, but it is less effective than a complete disassembly.
Why do I see sludge in my radiators?
Sludge in radiators is a sign that there are many impurities in your system that have settled on the walls of the pipes and radiators. This can be caused by corrosion, dirty water, or lack of filtration. We recommend cleaning the system and installing a quality filter to protect against further accumulation of impurities.
Is it important to filter the water before the boiler?
Yes, it is very important. The boiler is sensitive to impurities and corrosion. If the water entering the boiler is not filtered, it can lead to damage to the heat exchanger or pumps. Filtration before the boiler protects your system from expensive repairs and extends its lifespan.
Conclusion: An investment in filtration always pays off
Clogged filters and heating system failures are often the result of ignoring basic water treatment principles. As we have seen, impurities in the system can cause a range of problems, from reduced performance to complete system failure. Quality filtration and regular maintenance are key to maintaining the reliability and efficiency of your heating system.
Do not rely on the idea that a filter is "installed and forgotten." Actively monitor the filter condition, replace inserts in time, and pay attention to water quality. An investment in a quality filter and maintenance always pays off, as it will save you from expensive repairs and ensure comfortable heating for many years. If you have any questions or need help choosing a filter, do not hesitate to contact us. Our expert support will help you find the best solution for your system.
Do you have a question about this topic?
Struggling to decide or dealing with a specific situation in your home? Write to us – we are happy to help.