Common faults and problems of heating stoves
Why to Pay Attention to Radiators Even After Installation
A radiator may seem like a simple device at first glance - essentially just a system of parallel or cross pipes through which the heat transfer fluid flows. In practice, however, we encounter a surprisingly wide range of problems with this "simple" device. After decades of experience with heating technology, we know that the majority of complaints and service interventions are not related to a production defect in the device itself, but to incorrect installation, poor system adjustment, or normal wear and tear, which can be significantly delayed with a bit of care. In this article, we will go through the most common faults of straight radiators, their causes, methods of diagnosis and solutions - including when you can manage with DIY intervention and when it is appropriate to call a heating engineer.
If you are considering the selection of a new radiator, we recommend also reading our articles How to Choose a Straight Radiator – Dimensions, Performance and Material or Straight vs. Round Radiator - Differences and Selection. This text, however, is focused on already installed radiators and their operational problems.
Most Common Fault: Air in the Radiator and Cold Upper Pipes
If a customer calls saying that "the radiator is heating only at the bottom and the top is cold," in nine out of ten cases it is an air bubble in the upper part of the radiator. Air naturally appears in the system - during filling, after shutdown, after repairs to the system, or gradually through gas transfer through seals and plastic pipes of floor heating, if the radiator is connected to a combined circuit.
Physically, it is simple: air is lighter than water, so it rises and accumulates in the highest point of the radiator, where it hinders the circulation of the heat transfer fluid. The result is a cold top of the radiator, possibly bubbling and gurgling during operation.
What a Proper Air Venting Looks Like
The solution is relatively straightforward - the air vent valve, usually located on the upper pipe, is carefully turned with an air vent key or a screwdriver. We go into the procedure in detail in the article Maintenance and Air Venting of a Radiator, but here we recall the key principles:
- Before venting, reduce the pressure in the circuit slightly by closing the valve or proceed with a lower pump performance
- Always have a cloth or container ready under the valve - escaping water can spray out
- Open the valve slowly, at most half a turn
- As soon as a continuous stream of water without air bubbles starts to flow, close the valve
- After venting, check the pressure in the system and, if necessary, add water
If the radiator needs to be vented repeatedly (more than once a month), it is no longer a normal occurrence, but a signal that air is constantly entering the system - most often due to a leak at the circulation pump, a faulty automatic air vent valve in the boiler room, or insufficient pressure in the expansion tank.
Leaks - Dripping at Joints, Corrosion, Microcracks
The second most common category of problems is leaks. Here it is important to distinguish several types according to the location, as each has a different cause and solution.
Leak at the Screwing and Connecting Neck
The most common place for water leakage is the connection between the radiator and the connecting fitting (angle valve, thermostatic head, reducer). The cause is often an insufficiently tightened connection, a damaged or forgotten gasket, or the use of an unsuitable sealing material (e.g. hemp rope instead of teflon tape for a fine thread, or vice versa). When installing new radiators, such as Straight Radiator 450 x 1180 or the larger Straight Radiator 750 x 1500, we always recommend checking the connections after the first filling of the system and reaching the operating temperature, and if necessary, slightly tightening them - the material "settles" and the connection may slightly loosen after thermal expansion.
Corrosion and Perforation of the Radiator Body
A more serious problem is the corrosion of the radiator material itself. Steel radiators are more prone to corrosion than stainless steel, especially if oxygen is present in the system (typically in floor heating with plastic pipes without an oxygen barrier, or in the case of frequent topping up of fresh water rich in dissolved oxygen). The symptoms are typical - rust spots on the surface of the lacquer, later small dots from which water will eventually start to seep. In the early stage of corrosion, adjusting the chemistry of the heating water (corrosion inhibitors) helps, but in an advanced stage, perforation is irreversible and the radiator needs to be replaced.
Microcracks After Freezing
In unheated cottages, chalets, or in reconstructed buildings where the heat supply was interrupted during the winter, we often encounter cracked radiators after the water inside them froze. Water expands by approximately 9 % when frozen, creating extreme pressure in the enclosed space of the pipe. Cracks most often occur at bends or welds, where the material is most stressed. A radiator with frozen water should not be thawed with sudden heating (a blowtorch, hot air gun) - further damage is a risk. The correct procedure is to slowly thaw it at room temperature and then thoroughly check the tightness before reconnecting it to the system.
Uneven heating and "cold stripes" with horizontal radiators
In some constructions of straight panel radiators, where the main flow is supplied by one vertical pipe and the cross pipes are only supplementary (so-called secondary circuit), it may happen that individual cross pipes are heated unevenly — one is hot, the adjacent one is warm. This is not necessarily a fault, but a consequence of the design and low flow. With low pump performance or with a very long radiator body (for example, Straight radiator 750 x 1500), the heat transfer fluid does not have time to distribute evenly to all cross pipes, especially if the system is set to a low heating water temperature (typical with heat pumps).
A solution is often to adjust the flow through the thermostatic valve, or to reassess the sizing of the circulation pump. In practice, we have also encountered cases where a customer complained about "uneven heating" of a radiator that was actually in perfect condition — the customer simply expected the same feeling of warmth as with a classic panel radiator, while the radiator is structurally different and radiates heat in a partially different way.
Problems with reverse connection and cross flow
During installation, especially when done by the user themselves, it can happen that the installer or the owner confuses the supply and return pipes. In some radiator types, this causes only a slight reduction in performance, while in others (especially those with an internal partition or more complex flow geometry), it can lead to a significant drop in performance, as the water "short-circuits" through a shorter path instead of passing through the entire body.
Typical symptom: the radiator is warm only in the lower or only in the upper part, with no air in the system (the situation does not change after bleeding). In such a case, the direction of connection should be checked according to the manufacturer's technical data sheet, and if necessary, the supply pipes should be swapped. We also recommend reading our article on How to connect a radiator to central heating or electricity, where this issue is discussed in more detail with connection diagrams.
Noise in the system — bubbling, knocking, hissing
Acoustic issues with radiators are less common than thermal problems, but can be more annoying, especially in the bathroom, where sound travels surprisingly far through tiled walls.
Bubbling and gurgling
Almost always, this is again due to air in the system, or an excessively high flow through a throttled valve (cavitation). The solution is to bleed the system and, if necessary, adjust the flow on the thermostatic valve to the recommended range.
Knocking during startup and cooling
Knocking that appears shortly after turning on the heating or, conversely, after turning it off, is related to thermal expansion of the material. A metal radiator body expands by tenths of a millimetre to a millimetre (depending on length and material), and if it is tightly clamped in improperly dimensioned brackets or the bracket is too tightly fastened to the wall, friction and a characteristic "click" occurs. The solution is to check the mounting — the brackets should allow minimal movement, not be tightened with a forceful grip on the pipe.
Hissing at the valve
A hissing sound at the valve indicates either an excessive pressure difference (incorrect setting of the differential pressure on the circulation pump), or a partially clogged filter/mesh before the valve, which restricts the flow to a small cross-section and causes turbulence. In older installations with neglected system maintenance, this is a fairly common occurrence.
Problems with electric and combined radiators
With electric heating radiators (or combined ones, which have an electric heating rod alongside the water circuit for summer operation), we encounter a different group of faults:
- The rod does not heat at all — most often due to a faulty thermostat, a broken cable in the supply, or a burnt heating element in the rod. It requires inspection with a multimeter, ideally by an electrician or service technician.
- The rod is heating constantly, even after being turned off — a typical sign of a stuck relay or a damaged thermostat; the radiator then overheats and damage to the sealing of the filling (in rods filled with oil or water) is a risk.
- Leakage current, tripping of the circuit breaker/RCD — humidity in the bathroom is a demanding environment; with damaged cable insulation or a leaky sealing of the heating rod, moisture can penetrate into the electrical part. This is a safety risk and must be addressed immediately — disconnect the radiator from the power supply and have it inspected.
- Malfunction of the switching valve in combined radiators — if the switching (three-way) valve between the heating circuit and the electric rod is not in the correct position, it may happen that cold water from the turned-off heating flows through the radiator alongside the activated electric rod, significantly prolonging the heating time and increasing electricity consumption.
Diagnostic procedure step by step
When we receive a query such as "the radiator does not heat" or "the radiator heats poorly," we recommend the following procedure, which we can also recommend to customers before calling in a service technician:
Common installation errors from practice that later appear as "faults"
A large portion of the complaints we encounter in practice are not actually product faults, but the result of installation errors. We will mention several typical scenarios:
Scenario 1: Ladder mounted too low from the floor
The customer installs the radiator body according to their own estimate, without following the recommended height from the floor (usually 15-25 cm depending on the type). As a result, there is not only an increased risk of foot impact and mechanical damage to the lower pipes, but also problems with the installation of floor heating covers or floor profiles. The recommended installation procedure, including the spacing of anchoring points, can be found in the article Installation of a heating ladder on the wall - spacing and procedure.
Scenario 2: Undersized ladder, "the bathroom is always cold"
A very common case - the customer buys a smaller ladder type, such as Straight ladder 450 x 740, for a larger bathroom with two external walls. The radiator functions correctly, but it cannot cover the room's heat loss. This is not a fault, but an error in selecting the power - we recommend calculating according to our article What heating ladder power do you need per m2 of bathroom before purchase.
Scenario 3: Improperly tightened consoles causing body waviness
With longer ladders, such as Straight ladder 750 x 1500, the placement of anchoring points along the entire length and height of the body is crucial. Using only two end consoles instead of the recommended number (usually 4-6 points depending on the size) leads to slight bending of the body due to its own weight filled with the medium, which over time stresses the welds and can lead to microcracks precisely at the point of greatest stress.
Scenario 4: Missing or incorrect thermal insulation under the plaster
In renovations, where the piping runs in the wall under the tiling, it often happens that without sufficient pipe insulation, heat losses occur even before the radiator itself, and the ladder thus receives water at a lower temperature than it should. The customer perceives this as a "weak radiator performance," while the cause is in the piping route, not in the body itself.
Prevention - how to extend the trouble-free lifespan of the radiator
Many faults can be avoided by simple, yet regular care:
- System pressure check at least once per heating season, ideally at the beginning of autumn before starting heating
- Defoaming after any major intervention into the system - radiator replacement, pipe repair, water topping up
- Visual inspection of connections once every six months, especially in the bathroom, where humidity makes it harder to detect minor leaks in time
- Chemical treatment of heating water in systems with a mix of materials (copper, steel, aluminum) - a suitable corrosion inhibitor significantly extends the life of all metal parts
- Preventing freezing in unheated areas - if the building is unheated during winter, the system should either be drained or filled with a non-freezing mixture suitable for heating systems
- Avoiding excessive mechanical load on the radiator - a heating ladder is not designed as a load-bearing element for drying heavy laundry or as a support; excessive mechanical stress shortens the lifespan of the welds
When is it a complaint and when is it normal wear and tear
From the seller's perspective, it is important to distinguish between a manufacturing defect in the body (for example, a faulty weld that cracks within a few months after installation without an obvious external cause, or uneven material thickness causing premature corrosion) and the result of incorrect installation, maintenance, or operating conditions (freezing, mechanical damage, unsuitable water chemistry, direct action of aggressive cleaning agents on the surface treatment).
In the case of a complaint, it is always useful to have photographic documentation of the damage, information about the installation date, type of system (central heating, electricity, combined), and if possible, data on pressure and temperature in the system. These details significantly speed up the evaluation of the complaint and finding the correct solution.
Frequently asked questions (FAQ)
Why is my radiator heating only at the bottom and the top is cold even after defoaming?
If defoaming did not help, it is likely due to an incorrect connection direction (supply and return swapped), insufficient flow through a throttled valve, or in the case of longer bodies, a low performance of the circulation pump, which cannot push the medium through the entire height of the radiator. We recommend checking the setting of the thermostatic valve and, in case the problem persists, calling a heating technician to check the flow conditions.
How often should I defoam a heating radiator?
In a properly functioning, closed system, defoaming should be needed only occasionally - typically at the beginning of the heating season. If you need to defoam more often than once a month, there is likely a constant source of air in the system, and you need to find its cause, not just solve the effect by repeated defoaming.
Can I leave a radiator connected to central heating completely empty of water during the summer?
We do not recommend draining the system just for the summer break - an empty radiator is more susceptible to internal corrosion caused by contact of metal with oxygen in the humid air. It is better to keep the system filled and, in the case of a combined radiator, switch to the electric rod, or in the case of a purely water radiator, maintain a minimal flow through the bypass.
My radiator cracked after freezing, can it be repaired by welding?
Technically, a repair by welding is possible, but we do not recommend it as a permanent solution in the case of visible damage to thin-walled pipes of the radiator - the material around the crack is weakened by repeated thermal stress, and the risk of a new leak is high. In the case of visible deformation or cracking, it is usually more economical and safer to replace the radiator.
Why is the residual current device tripping on my electric radiator?
This is a safety issue caused by a current leak, most often due to moisture entering the electric heating rod or damaged insulation of the supply cable. We do not recommend using the radiator in this condition - disconnect it from the power supply and contact a service technician, as it is a matter of safety, not just comfort.
How can I tell that I have a corrosion problem on my radiator before it starts leaking?
The first sign is usually small rust spots or dots on the surface finish, especially around the welds and bends. If you notice such areas, we recommend not waiting for perforation - check the chemistry of the heating water and, if necessary, add a suitable corrosion inhibitor to the system, which can significantly slow down the progression of corrosion processes.
Summary
The majority of heating radiator faults fall into several recurring categories - air in the system, leaks at connections, corrosion, incorrect wiring, or installation errors. In most cases, diagnosis and resolution are relatively simple if approached systematically: first check the most likely causes (air, valves), and only then look for more complex reasons (body damage, pump failure, design errors in the heating system). When choosing a new radiator, whether it is a compact Straight ladder 450 x 740 for a small bathroom or a larger format such as Straight ladder 750 x 1180 for a family house, it pays to pay attention not only to power and dimensions, but also to the quality of installation and regular maintenance - an investment of just a few minutes per year in checking pressure and defoaming can save considerable costs on repairs or premature replacement of the radiator.
Do you have a question about this topic?
Not sure or dealing with a specific situation in your home? Write to us - we are happy to help.