If the pressure in the boiler rises

Why the pressure in the gas boiler drops or rises: the causes of unstable pressure ways to prevent problems

The work to ensure the proper functioning of heating equipment does not end with its installation. Maintenance requires a certain level of knowledge on the part of the owner and constant monitoring of the system. It is important to understand why the pressure in the gas boiler drops or rises, and why the equipment operates with the drops.

In the article presented by us described in detail all the causes of pressure instability in the system for the preparation of coolant and hot water. We will tell you how to troubleshoot and keep the figures in the normal range. Our recommendations will help to cope with the impending breakdowns and prevent malfunctions.

Pressure in closed heating systems

With the help of a circulating pump in the heating system creates diminishing pressure.

Due to this, the closed system has the following advantages:

  • The length of the heating circuit increases in direct proportion to the pump power;
  • Batteries can be connected in series or in parallel. the heat is distributed more evenly when connected in parallel;
  • the possibility of installing pipes of small diameter ;
  • gas economy. Since the coolant has a higher velocity than in open systems, it does not cool down as much
  • to relieve the excess head. it is possible to reduce the capacity of the circulation pump;
  • the possibility of choosing the pump capacity to overcome hydraulic pressure and depending on the length of the circuit and the diameter of pipes.

Air pressure in the expansion tank

The pressure value of air or nitrogen in the expansion tank for different gas boilers will not be the same, it all depends on the type of equipment and design features. The standards are specified by the manufacturer in the product data sheet.

Usually the pressure in the new damping tank is 1.5 atm. But this setting may not be suitable for a particular heating system. Factory parameters are easy to reset. For this purpose, the body of the expansion tank has a special nozzle (some manufacturers have it as a spool for pumping), through which the air pressure is regulated.

The nipple is on the side of the air chamber of the cylinder. It can be used to release excess pressure or, conversely, to inflate the tank

For normal operation of the gas boiler needs to be in the membrane tank pressure was less than 0.2 atm than in the system itself. Otherwise the increased volume of hot water will not be able to enter the tank.

In smaller buildings and apartments for closed heating systems, a pressure of 0.8 to 1.0 bar (atm) in the expansion tank is generally acceptable. But not less than 0.7 bar, since many gas boilers are protected and the device simply will not turn on.

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Check the pressure level of the tank should be checked annually. If you notice pressure spikes in the heating system, it means that the air is out of the damping tank and it must be pumped.

Norm and control

We have already said that the pressure in the gas boiler should be within 1.5-2 atmospheres. this is the norm for the system, which is put into operation and is in the warmed up state. In high-rise buildings heated by centralized boilers, this indicator is higher. Here pipes and batteries must withstand not only the high pressure, but also hydro. is a sudden increase in pressure.

If for centralized systems the fluctuations are typical, then for the autonomous heating they are rare. the volume of coolant is not so great that serious jumps can be observed. In a cold state the normal value is 1-1,2 atm., and a little higher in the heated state.

Autonomous heating systems powered by single and double loop boilers are used in private households. The latter are becoming more widespread. In addition to heating, they solve the problem of hot water preparation. One circuit in them heats the coolant circulating in the pipes, and the other provides the operation of the hot water system.

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The main reasons for the pressure increase

Most often the reason why the pressure in the heating circuit in a closed heating system is growing, is the equipment failure due to which the figures jump up and then drop sharply down. But in addition to this, the causes also include the following:

  • Sudden increase in pressure of heat carrier due to blocked shutoff valves. There is an increase in pressure in the system, after which the boiler is blocked and the system shuts down. To fix the problem, check fittings for leaks, open valves and valves to relieve pressure.
  • Higher pressure in a heating system can be caused by a clogged strainer. On the surface of such filter particles of rust, debris, sand and slag accumulate. As a result, the pressure in the area between the boiler and the filter rises strongly. To eliminate the cause, it is necessary to clean the filter regularly, at least 3-4 times a year. Replacement of common strainers with magnetic or flush filters would also be a good solution. They cost more, but their maintenance is much easier.
  • The operating pressure of the system can increase due to malfunction of the heating boiler automatics. It is a factory defect, wrongly made settings of the system, the breakage of the control board. All these problems require repair of the boiler, which can only be carried out by a master.
  • Leaks in the make-up cocks are observed, that is, the water will constantly penetrate into the general circuit, causing a pressure jump. Repair is usually quite simple, you only need to replace the rubber gaskets. But if there is a defect, the entire valve or equipment must be replaced.

Why the pressure drops in a two-circuit or conventional boiler? This situation most often occurs when the expansion tank is broken or the air valve is missing. To fix the problem you may need to repair or completely replace the tank.

Low water pressure in the boiler. what to do?

If no leaks are detected in the radiators, then the cause of why the pressure drops is in the boiler. Why it happens and how to raise (gain, pump up, increase) the pressure? If you frequently pump water, and the boiler does not hold pressure, there is a chance that microcracks have formed in the heat exchanger. When the boiler heats up, the cracks enlarge and leakage. Urgent intervention of a specialist or the fistula can be repaired with your own hands.

Soldering of the heat exchanger

The reason of micro cracks appearance is the exchanger wear and tear, frequent flushing with reagents, poor quality of metal of which it is made, water hammer due to the sharp increase of pressure in the line. They usually occur after an accident in the water mains.

Locations where there are micro cracks can be identified by the layer of scale. If it is not difficult to remove the heat exchanger, you can try to solder them. Bi-thermal heat exchangers are almost impossible to repair because of its design features, it must be replaced.

Boiler does not rise (does not gain pressure) when make-up valve leaks. If the pressure in the main line is higher than the pressure in the boiler, the liquid through the make-up valve increases the pressure in the boiler to a critical point, is discharged through a safety valve.

As a result, the pressure decreases, the water from the heating system presses the liquid in the plumbing and heating system. Close the tap, check the connection for leaks or replace it if it is defective.

Pressure drops to 0 when there is a problem with the three way valve. Large pieces of scale or rust can get into the valve and obstruct the flow, clean the valve.

The problem with the expansion tank can cause pressure changes. When heating increases the volume of water in the system, this excess flows into the expansion tank. There is a rubber diaphragm inside the tank.

The space between the outer wall and the tank membrane is filled with gas. Excessive liquid fills the diaphragm and causes depressurization of the heating system. The gas equalizes the excessive pressure.

After the temperature drops, the liquid flows back into the system. This does not occur in the case of a gas leak. If the equalising tank is not functioning properly, the valve nipple is worn and must be replaced. Worse, when the diaphragm is torn, the tank itself must be replaced.

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The expansion tank in a cut

A car pump can be used to pump air into the expansion tank. How to add (supply, pump up) pressure in the expansion tank?

When the turned off boiler cools down, it is necessary to carry out the following steps in the exact sequence:

  • Close all the supply and return flow valves and cocks.
  • Drain all water from the boiler using a drain valve until the pressure gauge reads “zero”.
  • Check the water pressure in the equalising tank; it must be empty.
  • Connect the pump to the expansion tank spool and inflate until no more water leaks from the drain fitting.
  • Bleed. To bleed air from the system
  • Re-pump to the pressure gauge values given in the machine’s data sheet.
  • Close the drain connection.
  • Open the supply and return valves. Start the unit.
pressure, boiler, rises

If inflation quickly causes the pressure to drop and air to escape through the connection tubing, this indicates a ruptured diaphragm.

See pressure gauge data sheet for some wall mounted models. Pressure gauge failure. this can happen if the connection that connects the pressure gauge to the unit is clogged. Clean it and if that doesn’t help, replace the pressure gauge.

Find and repair the defective assembly

To determine leaks in a closed heating circuit it is necessary to inspect the detachable and fixed elements of the pipeline and radiators, water taps, threaded joints, welding and soldering sites, and Mevsky cocks. check for continuity. If found under radiators, pipes, etc. д. water accumulation, determine the cause of water accumulation. Puddles can form under threaded connectors (at sharp temperature changes this type of connection unscrews spontaneously), poor quality soldered or welded joints, parts with microcracks. To stop the leak at a threaded joint, it is sufficient to pull the assembly. In rare cases the sealing insert must be replaced. To carry out the revision of the part, the section with the defect, it is necessary to make a partial or complete drainage of the heat supply line.

There is a direct correlation between a leaking make-up valve and the pressure in the central water supply. If the water pressure increases or decreases, the pressure in the boiler also changes, although the boiler make-up valve is in the closed position. Usually the pressure in the central pipe is 0.5. 3 bar. If you do not find a leak in the heating circuit, monitor the pressure changes in the boiler and the central pipeline. If a direct correlation is detected, replace the make-up valve (on non-disassembled models) or replace the sealing sleeve (on models with removable stem).

Sometimes, for some reason (outdated model, unavailable for purchase, etc.), the boiler is not in operation. д.), it is not possible to buy a new gate valve, then you can connect the pipes: the cold water supply to the boiler and return from the heating circuit, using a conventional shut-off valve.

Schematic layout of the make-up valve of the heating system.

At the same time the regular make-up valve must be in the closed position and not let water in. If it is badly worn out, it must be dismantled, the stem must be raised, the inner holes must be filled with silicone and the valve must be set in the closed position. To mount the valve in its original position and no longer use it for its intended purpose. But these manipulations should be performed only in extreme cases.

The pressure in a closed heating system also changes due to the large amount of air that is not evacuated from the system. Although modern boilers are equipped with automatic air vent valves, they may malfunction due to scale fouling. Carefully inspect the air vent for foreign buildup. It is usually located near the circulation pump.

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Air vent of the wall hung gas boiler.

If scale is present, clean the air vent. Using a flat screwdriver, lift its cap and turn on the pump in circulation. If such function is absent in your model of boiler, start the boiler in a heating mode. All air will escape from the pipes and radiators. Also, the air can be removed through the cocks Maevsky, which should be equipped with all heating radiators at the top point.

The Mayevsky valve in the upper point of the radiator.

Disturbance of integrity of membrane, spool, as well as reducing the pressure in the air cavity of make-up tank leads to a dynamic pressure change. Before examining the condition of the expansion tank, determine the place of its installation. To check the tightness of the diaphragm and the mechanism for pumping air, unscrew the cap from the spool valve.

Signs of the expansion tank membrane leakage.

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Presence of water inside the valve indicates that the diaphragm is damaged. In this case, since the tank is sealed, it becomes unrepairable and must be replaced by a similar one. Appearance of bubbles from the operating orifice of the distributor moistened with liquid indicates wear of the spool o-ring. Screw in the valve core or replace it.

The listed measures are proven and are among the effective ways to restore stable coolant pressure in a closed heating circuit.

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Causes of increased pressure due to an air lock in an open system

In an open system with a properly designed slope, all air is removed through the expansion tank. Air s can arise only if the system is incorrectly filled with water during start-up or after repairing radiators.

In the case of such problems the air can be easily blown out through the Mayevsky cocks on the radiators. If it is not possible to reduce the pressure, you may need to completely drain the system and restart it.

The first boiler start-up and the adaptation period

For the possibility of warranty service of your unit, the first start-up must be carried out by a service organization. The boiler can only be put into operation after the construction and repair work, in the room where the boiler is installed.

A test run of a two-circuit boiler consists of the following activities:

  • compliance with the installation requirements;
  • checking of tightness of all units and connections;
  • start-up of the unit, adjustment of parameters;
  • putting the boiler into warranty service.

Initially, using the make-up valve, which is usually located at the bottom of the unit, the system is slowly filled with water. Pay attention to the pressure gauge readings. The pressure must be within the limits specified in the instructions of the particular appliance. As soon as the manometer shows a sufficient value, the make-up valve must be closed.

then you need to remove the residual air from the radiators and circulation pump. Most modern models are equipped with an evacuation device, but they do not always give the desired result.

Use the Mayevsky tap to bleed air from the radiators, open the tap until the water flows from the radiator. After deflating all the radiators the pressure in the system drops, so you need to recharge it with water to the desired pressure.

The circulating pump is then vented. After opening the lid of the boiler, turn on the unit. At the same time you will hear the pump will turn on, emitting a hum, gurgling. These sounds indicate that it is blocked. Using a screwdriver, slowly unscrew the bolt that is in the center. After water appears from underneath it, the bolt is screwed back in.

This should be done several times until all the air is bled out. You can tell by the even sound. Next, the electrical ignition should work and the boiler will start. Keep an eye on the pressure gauge; if the pressure drops, add water.

While the system is warming up, unscrew the furthest radiators to full, the nearer ones, on the contrary, by taps, which are located on the radiators. The adaptation period usually lasts for several days, when you need to regularly bleed and add liquid to the system.

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