Troubleshooting common faults in hot water heating systems

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This post was last edited by “Hasty Passerby” on October 23, 2018, at 09:01. Troubleshooting common faults in hot water heating systems. Currently, hot water heating is widely used in both industrial and residential buildings. However, due to the lack of experience among the construction workers in the installation, adjustment, and operation management of hot water heating systems, some faults may occur during operation, affecting normal heating. Based on years of field experience, several common faults in hot water heating systems and their solutions have been summarized for your reference. 　　I. Local radiators are not hot The reasons why local radiators are not hot are generally as follows: the valve is malfunctioning, and the valve disc has fallen into the valve seat, blocking the flow path of the heating medium. In such cases, the valve cover can be opened for repair, or the faulty valve can be replaced. Excessive air stored in the air collection tank can block the pipelines, resulting in some radiators not heating up. In such cases, it is necessary to use the venting devices provided in the system, such as the exhaust valve on the air collection tank or the manual vent valves on the radiators. 　　In case of a pipe blockage, when the water supply duration is relatively short, one can feel the temperature at the bends in the pipeline and in front of the valves by hand, while also tapping on the pipes to listen for any unusual sounds. However, when the water supply lasts for a long time and the system is quite large, dead-water sections form both before and after the blockage site; in such cases, it becomes difficult to pinpoint the location of the blockage by touch alone. In this situation, draining water can be used as a method of detection. The draining process should be carried out sequentially from the midpoint of the non-heating section of the pipeline towards both ends. During water discharge, if the hot water from the inlet continues to flow forward, it indicates that the blockage lies after this point. Then, water is discharged from a middle section of the remaining pipe segment; if the hot water no longer continues to flow forward in this section, it means the blockage is located between the first and second discharge points. Once the blockage is located, the section of pipe is opened, the debris inside it is removed, or that section of pipe is replaced. 　　The improper installation of the slope in the pipes of the heating system causes the pipes to bulge, resulting in air pockets forming inside them. These air pockets block or reduce the flow cross-sectional area of those pipe sections, thereby leading to localized areas that do not receive adequate heat. At this point, the slope of the pipe section should be adjusted to meet the required slope and direction as specified in the design. 　　The supply and return pipes of the indoor system are connected in the opposite order to those of the outdoor heat network, or all connections are made on the supply (or return) pipes, preventing the indoor system from forming a circulation loop. At this point, a thorough investigation should be carried out to understand the situation on the external network, and the incorrectly connected pipes should be corrected. 　　II. Thermal failure When a dual-tube upper-split heating system is used, the radiators on the upper floors of multi-story buildings overheat, while those on the lower floors undercool. There are two possible reasons for this vertical thermodynamic imbalance. 　　Firstly, the heat transfer fluid flow rates between the upper and lower radiators differ significantly. The way to troubleshoot this issue is to partially close the valve on the upper radiator branch pipe, thereby reducing the flow rate of the heat medium. 　　Secondly, the lower section of the branch pipe is clogged with mill scale, scale, etc., which increases the resistance in this circulation system and disrupts the balance of pressure losses across various loops in the system. In such cases, it is necessary to remove the debris from the pipe sections promptly or replace the support pipes, in order to reduce resistance losses and restore the balance of pressure losses among the various loops of the system. 　　When a bottom-fed system is used in multi-story buildings and the radiators on the lower floors overheat while those on the upper floors do not, the reason may be air trapped in the radiators on the upper floors. It is necessary to check the air release valves on the radiators or the exhaust valves in the piping to remove the air. It could also be that there is a water shortage in the system, in which case water needs to be added. 　　When there are several parallel circuits in the same system, it sometimes happens that some circuits overheat while others do not, resulting in a imbalance. In such cases, the main control valves on each circuit should be adjusted to equalize the pressure losses between the circuits, thereby eliminating the uneven distribution of heat among them. 　　In a two-pipe system, when the radiators at the far end remain cold while those near the heat entry point become overheated, this also constitutes a phenomenon of horizontal thermal imbalance. The reason for this phenomenon is that the upstream valve is open wide, resulting in an imbalance between the operating pressure of each loop and the pressure lost within that loop itself. Near the inlet end of the main pipeline, the fluid passing through the radiators has a shorter path, resulting in less pressure loss and thus a larger residual pressure. As a consequence, the flow rate of the fluid in those loops becomes too high, exceeding the actual requirement. The heat transfer fluid in the remote radiator has to travel a long distance, resulting in significant pressure loss; as a consequence, the flow rate of the heat transfer fluid through the remote circuit decreases. At this point, the valve on the loop branch pipe at the system inlet should be closed, while the vent valve on the end collection tank should be opened, or the automatic exhaust valve should be checked, in order to remove any remaining air from the system. 　　III. Excessively high return water temperature The circulation valve on the return pipe at the inlet device of the heat users is not closed or is not closed properly; in such cases, each inlet device should be checked to ensure that the circulation valves are properly closed. 　　When the system’s heat load is low, the circulation water volume is high, and the amount of heat supplied is large, it is necessary to adjust the main inlet and return water valves in order to increase the system resistance and thereby reduce the circulation flow rate. 　　The boiler’s heating capacity is excessive, resulting in low consumption in the heating system and excessively high supply and return water temperatures. In such cases, the upper limit of the supply water temperature should be controlled. When the water supply temperature reaches a certain value, corresponding measures are taken in the boiler room, such as shutting down the blowers and exhaust fans. 　　IV. Excessively low return water temperature of the system The reasons for an excessively low return water temperature in the system are generally as follows: the boiler installed as the heat source is unable to supply sufficient heat, resulting in the supply water temperature not meeting the design requirements. At this point, the boiler should be modified or an additional one installed to increase the water supply temperature. If the flow rate of the circulation pump is low or its head is insufficient, the circulation of the heat medium in the system will be slow, and the temperature difference between the water supplied and the water returned will be large. In such cases, an appropriate circulation pump should be selected to replace the existing one. There is a serious leak in the outdoor pipeline network; the pressure in the boiler room drops too rapidly, and the amount of make-up water for the boilers far exceeds the normal requirement. In such cases, an inspection of the outdoor pipeline network should be conducted to identify and promptly repair any leak points. The high heat loss in the external piping system can sometimes be the main cause of excessively low return water temperatures. Factors contributing to such excessive heat loss include poor quality insulation in the external piping system, with some pipes not having any insulation at all, as well as the use of insulation materials of poor quality. Inadequate sealing between the manhole covers allows groundwater to flow into the manholes, or leaks in the pipes within the manholes result in an excess of water there; this causes both the supply and return pipes to be submerged in water, turning the manholes into large-scale heat exchange stations. In such cases, it is necessary to improve the insulation and maintenance of the outdoor piping system, and to remove any accumulated water from the manholes promptly. 　　The circulation water volume is too low. In this case, check whether the pump is running in reverse, whether the pipelines, orifice plates, valves, etc. are clogged, or whether the valves are not fully open. Open the valves and remove any dirt and sediment from the system at the same time. 　　V. Other faults and troubleshooting methods A large fluctuation in the water supply temperature can cause the radiator and pipe fittings to expand and contract due to heat, leading to leaks. In such cases, appropriate measures should be taken to maintain a stable temperature of the water supplied to the boiler. 　　The heights of the buildings vary greatly; in some of the buildings in the system, excessive pressure during operation causes damage to the cooling equipment and accessories, leading to leaks. In such cases, it is necessary to request the technical department to install pressure regulating valves on the water supply pipes at the heating inlet devices of those buildings, based on the water pressure required for each building. For those already equipped with pressure regulating valves, the diameter of these valves should be adjusted. Where possible, automatic pressure relief devices can be installed at the system inlet in the lower-rise buildings. 　　With further advancements in science and technology, hot water heating technologies will continue to improve, and heating systems will become more sophisticated, thereby providing a comfortable environment for people’s work and living spaces, ensuring human health and promoting the modernization of our country. 　　I. Heat source: (28 factors in total) 1.1. Water supply factors: 1.1.1. Low set pressure: The set pressure of the water supply pump is low, resulting in insufficient heating in the tall buildings within the system. 　　1.1.2, Makeup pump failure: The makeup pump is malfunctioning, and there is no backup pump, resulting in a severe water shortage in the system. 　　1.1.3 Inverter failure: The inverter of the make-up water pump malfunctions, resulting in delayed make-up water supply. 　　1.1.4 Low water level in the expansion tank: The expansion tank runs low on water due to reasons such as a malfunctioning water replenishment signal. 　　1.1.5: Small make-up water tank: The system is severely short of water, and the capacity of the make-up water tank is not sufficient to meet the water replenishment needs. 　　1.1.6 Water outage: Caused by accidents; this situation may also occur in other cities facing water shortages, resulting in an inability to supply water. 　　1.2 Cyclic factors:
1.2.1 Circulation pump failure: If the circulation pump malfunctions and there is no backup pump, the system cannot circulate. 　　1.2.2 Intermittent cycling: To save electricity, some heating management units often shut down pumps, resulting in unstable system operating conditions. 　　1.2.3. Low flow rate of the circulation pump: This results in large areas where users feel no heat. 　　1.2.4 Low head pressure of the circulation pump: results in insufficient heating for end-users. 　　1.3 Boiler-related factors: 1.3.1 Small boiler capacity: The heating capacity of existing boilers fails to meet the actual needs of users. 　　1.3.2 Low boiler efficiency: The boiler capacity appears to meet the requirements, but low efficiency results from factors such as incomplete combustion of fuel, high exhaust temperatures, severe scaling in the boiler’s water circuits, and high heat loss from the boiler’s surface, which leads to insufficient heating during cold periods. 　　1.3.3 Shutdown: The boiler is malfunctioning; there is no backup boiler, and it is currently under maintenance. 　　1.3.4, Substandard fuel: The use of low-quality fuel with a low calorific value can make it difficult to start the furnace or cause it to shut down frequently. 　　1.3.5 Low fuel consumption: Some heating management units, focused solely on their own economic interests, are willing to sacrifice the interests of heat users; they use less fuel than is necessary to meet the basic requirements of these users, resulting in a heating quality that falls short of standards. 　　1.4 Heat exchange factors: 1.4.1 Inadequate selection of heat exchangers: When a thermal station needs to perform secondary heat exchange, the heat transfer capacity of the existing heat exchangers fails to meet the actual requirements of users. 　　1.4.2 Heat exchanger scaling: Due to substandard softened water in the boiler room or heat station, or due to lack of maintenance over time, severe scaling occurs on the primary or secondary water streams flowing through the heat exchangers in such stations, **which affects the efficiency of heat exchange. 　　1.4.3 Heat exchanger damage: Faults such as cross-contamination between primary and secondary water occur in the heat exchangers in the thermal station. 　　1.4.4 Excessive bypass flow: A high proportion of mixed water in the supply and return water bypass pipes results in an excessively low temperature at the outlet of the heat source, leading to heating failures. 　　1.4.5 Mixing pump issues: When a mixing pump is used for heat exchange, an inappropriate mixing ratio can also result in too low a water temperature at the outlet of the heat source, leading to heating failures. 　　1.5 Management factors: 1.5.1 Unqualified boiler operators: Boiler operators in heating management units work without proper certification, and this is a common practice in some areas; even these units employ untrained amateurs who take on such tasks without any expertise. 　　1.5.2 Lack of organized management: Some heating operation units lack management mechanisms; their employees lack a sense of responsibility and are unaware of the characteristics of boilers and heat exchangers as well as the relevant regulations. 　　1.5.3 Inadequate adjustment based on weather conditions: During various stages of the heating period, and on each day within those stages, outdoor temperatures and weather conditions keep changing; however, improper adjustments by the heating management unit lead to errors in heating supply. 　　1.5.4 Intermittent heating: Many heating management agencies use an intermittent heating method; when temperature calculations are accurate, timing is well managed, and oversight is proper, it is normal for the room temperature to be normal while the heating system is not producing heat temporarily. 　　1.5.5 Poor management of intermittent heating: When some heating management entities adopt intermittent heating, inadequate technology and management often lead to situations where the radiators fail to heat up properly and indoor temperatures remain abnormal. This is unacceptable. 　　1.6. Other factors: 1.6.1. Power outage: The make-up water pump and circulation pump cannot be started. 　　1.6.2 Unstable voltage: When the voltage is low, the current is likely to exceed the rated value; in such cases, the pump must be stopped temporarily, which may lead to instability in the system’s operation. 　　1.6.3 Clogged strainer: This increases the overall resistance of the system, resulting in no heat delivery to end-users. 　　II. Heat network: (26 factors in total) 2.1. Balancing factors: 2.1.1. Hydraulic imbalance: This is the most common phenomenon in such systems, and almost none of the heating management agencies manage it properly; as a result, end-users often do not receive sufficient heat while users at the beginning of the system experience excessive heat. 　　2.1.2 Imbalance in the primary piping network: Large-scale municipal systems require more careful management of the pipeline network; when there is a pressure difference between supply and return water, or even a reverse pressure difference, the heat stations will fail to provide heat, affecting the users served by them. 　　2.1.3 Alternating heat sources: Some thermal power stations or heat users can be supplied with heat via multiple connected heat sources; for example, operational disruptions in the main municipal heating system can lead to temporary interruptions in heat supply. 　　2.1.4 Low opening degree of the branch valve: To achieve equilibrium throughout the entire piping network, it is necessary to limit the flow rate and pressure difference for users located in the middle and near sections; sometimes, keeping the opening degree of such branch or user valves too low can also result in a lack of heat supply in the nearby areas. 　　2.1.5 Large differences in resistance between branches: The resistance within the systems of two adjacent branches or two separate buildings can vary significantly, and the greater this difference, the more difficult it is to achieve balance between them. 　　2.1.6 High resistance on the end users: High resistance on the end users significantly increases the overall resistance of the system, which in turn causes substantial changes in the operating conditions of the water pumps; as a result, the flow rate decreases markedly, affecting other users who do not receive hot water. 　　2.1.7 Abnormalities in end-users: Design flaws, improper construction, poor management, and old buildings can cause irregular heating supply for some users. If such issues occur at the upstream stage, they can still be resolved, but when they occur at the end-user level, the nature of the problem changes fundamentally. 　　2.1.8: Users opening valves privately: Users open the valves in the inspection wells on their own for personal gain, disrupting the original heating balance. 2.1.9 Management interference: Heating system managers, whether still employed or no longer so, who have personal grievances with their own organization or certain users, who fail to get what they want through bribery, or who are at odds with the energy-saving companies they work with or compete with them for credit, may secretly adjust or even close the valves in certain inspection wells, thereby disrupting the original balance of heat supply. 　　2.2, Factors related to new buildings: 2.2.1, Located between old buildings: When a new building is situated between old buildings, it disrupts the original hydraulic balance; not only is the new building at risk, but it may also affect the heating system of the old buildings. 　　2.2.2: Small original main pipe diameter: The diameter of the main pipe or the branch pipes is not enlarged after capacity expansion, resulting in no heating in the new building or surrounding areas. 　　2.2.3 High resistance in new buildings: The internal systems in new buildings have high resistance (due to large areas, use of underfloor heating, individual metering, etc.), which often results in poor heating performance. 　　2.2.4 Located at the end: New buildings built at the end of the system where operating conditions are unfavorable result in poor heating performance; this problem is exacerbated if there is also high resistance within the building’s own systems. 　　2.2.5 Unplanned complications: Without consulting the heating management authorities, people connect pipelines privately, steal heating energy, and disrupt the heating balance in that area. 　　2.2.6 Intra-section branch: To save on piping materials, a branch is taken from the system in the front building and connected to the buildings behind; this causes overheating in the front section, while the high resistance in the back section results in less heating. 　　2.3, Factors causing damage: 2.3.1, Failure of branch valves: Issues such as rusting, falling of the gate plates, and severe water leakage occur in these valves, requiring them to be shut down and repaired, which results in their temporary inability to be used. 　　2.3.2 Pipe damage: Due to construction or material issues, as well as lack of maintenance over time, sudden pipe bursts can occur, resulting in significant water leakage. Repair work takes a long time, and it is especially difficult to identify the problem in buried pipe sections. 　　2.3.3 Damaged compensators: A large number of thermal compensators are used in thermal piping systems. Due to issues with the quality of these devices, improper maintenance and management (such as water that does not meet the required standards for softening), or lack of maintenance over time, they can suddenly burst and get damaged, resulting in significant water leakage. Repairing such issues also takes a long time; moreover, it is particularly difficult to diagnose problems with bellows compensators located in directly buried pipe sections. 　　2.3.4 Human-induced damage to the pipeline network: Disruptions in heat supply occur when heating facilities such as valves or pipes are stolen or damaged; this phenomenon is more likely to occur with underground pipelines. 　　2.4 Other factors: 2.4.1 Initial adjustment: At the beginning of heating operation, the pipeline network is still in the adjustment phase, and the system pressure is unstable. 　　2.4.2 Small pipe diameter: Reasons such as planning, design, construction, and management result in small diameters for the main or branch pipes of the pipeline network, which do not meet the requirements of the current situation, renovation, or development. 　　2.4.3 Water supply and return connection: If the valves connecting the water supply and return lines in the pipeline network are open or malfunction, it causes a short circuit in the system. 　　2.4.4 Air accumulation at high points: The pipeline network should have a slope, and exhaust valves should be installed at the high points along the route to release air at the beginning of operation. 　　2.4.5 Pipe network clogging: Clogs resulting from construction residues and accumulated dirt over time can affect the efficiency of heat supply. These clogs often accumulate in areas with lower pressure, thereby having a greater impact on those areas. 　　2.4.6 Clogged filters: Similar to the previous case, dirt accumulated over time as a result of construction activities remains in the filters within the piping system; if this dirt is not removed in a timely manner, it affects the efficiency of heat supply. 　　2.4.7 Poor insulation: Construction defects and poor management lead to poor insulation performance of the pipeline network, resulting in significant heat loss and heating temperatures that do not meet the required standards. 　　III. Interior building systems: (22 factors in total) 3.1. Design factors: 3.1.1. Vertical imbalance with supply at the top and return at the bottom: This system leads to temperature differences, with better conditions upstairs and worse conditions downstairs; the difference is even greater during the coldest times. When designing such systems, it is necessary to consider installing more radiators on the lower floors. 　　3.1.2 Vertical imbalance in the lower supply and lower return system: This system results in a pressure (difference) imbalance, with advantages on the lower floor and disadvantages on the upper floor; moreover, air tends to accumulate at the top. 　　3.1.3 Horizontal imbalance in asynchronous systems: When the horizontal main pipes of a building’s system are asynchronous, horizontal imbalance is more likely to occur, resulting in cold conditions at the ends of smaller systems. 　　3.1.4 Horizontal imbalance due to differential resistance: Due to design or modification reasons, when there are significant differences in the resistance of various vertical pipe circuits, horizontal imbalance can occur; for example, some vertical pipes may have only 1 set of radiators per floor, while other vertical pipes have 4 sets of radiators per floor. 　　3.1.5: The diameter of the riser is too small: This results in high resistance in the riser, low flow rate, and thus insufficient heating. When this occurs throughout the entire building, the total resistance of the building’s systems increases, adversely affecting heating. 　　3.1.6: Excessively large diameter of the riser: This results in high flow rate in this riser, low flow rates in the other risers, and thus insufficient heating. When the entire building is like this, the total flow rate of the systems within the building increases, which is detrimental to other buildings; moreover, it is difficult to adjust the flow rates, and vertical imbalances can occur easily if adjustments are attempted. 　　3.1.7 Unreasonable diameter change: Excessive sudden changes in the diameter of horizontal or vertical main pipes can easily lead to horizontal or vertical misalignment. 　　3.2 Valve factors: 3.2.1 Main valve on the top riser: When the main valve on the top riser is closed, fails to function, or is damaged (for example, if the gate plate falls off), it prevents flow in the circuit, resulting in stagnant water in all the radiators along the riser. 　　3.2.2 Main valve of the riser on the first floor: If the main valve of the riser on the first floor is closed, fails to function, or is damaged, it can prevent flow in the circuit, resulting in stagnant water in all the radiators along the riser. 　　3.2.3 Failure due to automatic air leakage: Most inexpensive domestic automatic exhaust valves last only 1–3 years, as the key component – the internal spring – often fails; it is advisable to use high-quality imported or joint-venture products instead. 　　3.2.4 Failure of the building’s entrance valve: This results in the entire building not having hot water temporarily, and repairs must be carried out as soon as possible to restore service. 　　3.3 Factors causing blockages: 3.3.1 Scale buildup: Dirty blockages occur due to high water hardness in this area, poor water softening performance, substandard pipe materials, and lack of maintenance over time, which leads to severe scale formation inside the pipes and affects the efficiency of heat supply. 　　3.3.2 Rust blockage: Sediment and dirt buildup caused by severe oxidation and corrosion inside the pipes, resulting from factors such as pipe materials, maintenance practices, and aging; this hampers the heating efficiency. 　　3.3.3 Construction-related blockages: Waste left over from rough construction gets stuck in the heating systems or pipes, preventing the heating from working properly. 　　3.3.4. Clogged filters: In systems with filters, such as individual household heating and underfloor heating systems, clogging of the filters can also result in certain areas within the system not being adequately heated. 　　3.3.5, Air blockage in the riser: The absence of an exhaust valve at the top of the riser, incorrect installation, or failure to exhaust air can all lead to air blockage, resulting in the riser not heating up. 　　3.3.6 Unreasonable slope: An unreasonable slope of the horizontal main pipes in the building’s system leads to air trapping, resulting in the system not heating properly. 　　3.4 Other factors: 3.4.1 Different adjustment methods: When adjusting the system inside the building, sometimes the supply valve is adjusted and sometimes the return valve, making it difficult to achieve pressure balance. 　　3.4.2 Lack of insulation: In gutters, corridors, or the homes of individual heat users, the horizontal or vertical main pipes lack insulation or have inadequate insulation, resulting in high heat losses or overheating of those users, and thus insufficient heating supply for other users. 　　3.4.3 Failure to follow the construction drawings: During construction, issues such as reversed water supply and return lines often occur, resulting in the heating system not working properly. 　　3.4.4 Unauthorized piping: Connecting pipes illegally within the building’s system for use in cottages, garages, basements, retail spaces, etc., which leads to problems with the system’s heating function. 　　3.4.5 Aging of PVC pipes: Materials such as PVC pipes are commonly used in new buildings to connect radiators, but the water temperature in these systems should ideally not exceed 60°C; however, this is often not the case in practice. Over time, this leads to severe aging of the pipes, posing potential risks at any time. 　　IV. Heat users: (24 factors in total) 4.1. Factors related to unauthorized modifications: 4.1.1. Excessively large radiators: When users modify the heating system on their own, by using radiators that are too long or an excessive number of radiators, this increases the resistance to heat delivery. In systems with single pipes, this has a negative impact on the heating supply for users both above and below. 　　4.1.2: The new radiators are too small: When users modify the heating system on their own, they choose smaller, newer radiators for aesthetic reasons, which results in insufficient heat distribution. 　　4.1.3: Thin diameter of new radiators: When users modify the heating system on their own, they choose radiators with thinner connecting pipes, which increases the resistance to heat delivery to the apartments. In a single-pipe series system, this also affects the heating performance of users both above and below. 　　4.1.4 Adding extra heating: To achieve a higher temperature, users add several more radiators to the existing heating system; for example, a set of radiators is added to those in the hallway to supply heat to the balcony. This increases the total resistance in that circuit, resulting in the existing heating system no longer being effective. 　　4.1.5 Moving the heating system privately: Users, for reasons such as aesthetic considerations, move the radiators to other locations on their own; improper connections resulting from unprofessional installation cause the heating system to not work properly or lead to water leakage. 　　4.1.6. DIY floor heating: The resistance of floor heating is much higher than that of the traditional heating methods, which results in users spending money unnecessarily without achieving proper heating; in a single-pipe series system, this further severely affects the heating performance for users both above and below. 　　4.1.7 Self-installed water pumps: Some users who previously did not experience low water temperatures installed water pumps on their own pipelines, altering the circulation in those local systems; as a result, the circulation volume of water in those users’ systems increased, while the surrounding users had insufficient water flow and thus experienced low water temperatures. 　　4.1.8 Competition to replace heating systems: As users on upper and lower floors compete to replace their heating systems for aesthetic reasons and to achieve higher temperatures, the radiators and piping systems cannot be kept moist through proper drainage on a yearly basis. This leads to severe oxidation and corrosion of these heating devices, as well as an increase in circulation resistance in the vertical pipes in those areas, thereby exacerbating the problem. 　　4.2 Human factors: 4.2.1 Uncontrolled air release: At the beginning of heating operation or during periods when the external supply is unstable, users rush to release water and air, creating a vicious cycle that results in a high volume of water needed for cooling. 　　4.2.2 Water theft by users: Some users (such as certain commercial establishments) steal water for mopping floors, removing grease, washing cars, etc., which results in a large amount of water needed for cooling and thus prevents the heating system from functioning properly. 　　4.2.3 Malicious water release: Some users deliberately release water, for example by attaching a faucet to the radiator in their bathroom and using a flexible hose to direct water into the drain, thereby warming up their own heating system as revenge for the lack of heat. 　　4.2.4: Users on the ground floor close their doors: When users on the ground floor refuse to open their doors or are not at home, it results in the shut-off of the vertical pipe valves, or prevents proper maintenance of the heating equipment inside the building, which in turn affects the users upstairs and causes a lack of heat supply for them. 　　4.2.5 Top-floor user closes the door: When the top-floor user refuses to open the door or is not at home, it causes the vertical pipe valve to close, preventing air release from the top floor and making it impossible to properly service the heating equipment inside, which in turn results in the lower-floor users not having heat. 　　4.2.6 Poor neighborhood relations: Intentionally shutting off the main valve of the household’s neutral pipe or destroying the heating system, thereby affecting users upstairs and downstairs. 　　4.2.7 Disconnection of heating due to unpaid fees: In some areas, since certain users fail to pay the heating fees, the heating management authorities shut off the valves for a particular household, unit, or even an entire building, resulting in a lack of heat supply for those users, and this can also affect those users in the same area who have paid their fees. 　　4.3, Household-related factors: 4.3.1、No exhaust valves: In system heating for individual households, it is necessary to release air from the highest point of each radiator; the absence of exhaust valves leads to air blockages and consequently no heating. 　　4.3.2、No air release from the system: In systems with individual heating, the presence of an exhaust valve does not ensure that air is released; as a result, air blockages occur and the system does not heat up. 　　4.3.3: Radiators mounted too high: In systems with individual heating, if the radiators are installed too high, it affects the heating cycle, leading to gas blockages as a particularly serious issue. 　　4.3.4 Thin pipes: In systems with individual heating, the total resistance is higher compared to other buildings; if the pipe diameter is even smaller, this problem becomes more severe, resulting in many users of such heating systems not receiving sufficient heat. 　　4.4 Other factors: 4.4.1 Damaged radiators: such as corrosion of the radiators or aging of seals. 　　4.4.2 Frozen radiators: If users fail to close doors and windows in cold weather, their radiators will freeze, resulting not only in a lack of heat in their own homes but also affecting other users along the main piping system. 　　4.4.3 Malfunction of the user’s valve: For various reasons, the valve at the user’s entrance or the valve on a particular radiator may malfunction, resulting in insufficient heating. 　　4.4.4 Maintenance of connected users: Users connected to the same system are under maintenance due to issues such as water leaks; the relevant valves have been closed, which results in all of these users not having hot water temporarily. 　　4.4.5 Opposite slope of the radiator: The slope at the location where the radiator is installed should facilitate air release; otherwise, air blockages are likely to occur, which is even more problematic when there is no exhaust valve on the radiator.