Why The Pressure In The Gas Boiler Drops Or Rises: The Causes Of Jumps And Regulatory Values

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

In the article we presented, we describe in detail all the causes of pressure instability in the heating fluid and hot water preparation system. We will tell you how to troubleshoot the problems and keep the values in the normal range. Our recommendations will help you cope with impending breakdowns and prevent malfunctions.

According to the article:

  • What is the pressure in the heating system
  • How to check the pressure in the boiler and the circuit
  • Causes of pressure increase in a gas boiler
  • Hot water pressure increase in a heating circuit
  • The main causes of pressure decrease
  • How the pressure in the boiler is affected
    • The expansion tank: Features of the device and volume
    • Air chamber pressure adjustment
  • Conclusions and useful videos on the subject

What should be the pressure in the heating system

Heating systems can be divided into two types - closed and open. In an open system a non-hermetic expansion tank has a pressure regulating function.

The tank is installed at the highest point of the heating circuit and serves to contain the heating medium which expands when heated, to carry away air and also acts as a safety valve. The operating pressure in such a system depends mainly on the temperature of the heating water.

Commonly closed heating systems are used for heating in houses and apartments. They are more efficient and safer but require constant pressure control.

Why the pressure in the gas boiler drops or rises: the causes of jumps and regulatory values

It is very important to monitor the pressure and the temperature of the heating medium and to react to any unusual symptom of normal operation of the heating system - knocking, frequent release of hot water via pressure relief valve, cold sections of the circuit

Pressure in a closed circuit occurs due to forced circulation carried out by a pump. Pressure deviations may lead to equipment breakdown.

Why the pressure in the gas boiler drops or rises: the causes of jumps and regulatory values

The nominal pressure in different models of gas boilers may vary and is determined by the technical characteristics of the equipment

Designing the heating system, the pressure is calculated taking into account the height of the water column, the length of the system, the characteristics of the equipment connected, the cross section of the pipes.

For the adjustment of the operating pressure, the following data must be observed:

  • The technical characteristics of the gas boiler.The manufacturer indicates the boiler possibilities and the adjustment parameters in the instructions.
  • The temperature of the heating medium.The higher the temperature, the higher the pressure in the circuit, the lower the pressure is. Therefore the pressure in the gas boiler and the heating circuit should be adjusted and measured before and after the heating medium.
  • Volume of circuit and expansion tank.The size of the pressure tank has a direct influence on the pressure in the heating circuit, on its variation range.
  • The permissible pressure values for the least \"weak\" system element. The system pressure must not exceed the permissible values for each of the system elements. For instance, polypropylene pipes that are designed for an average pressure of 25 bar at a heating medium room temperature may only bear a pressure increase to 7-9 bar at 90°C.

The minimum pressure in the circuit may be 0.5-0.8 bar, the exact values are given in the instructions and the pressure sensor is adjusted to the required value according to these specifications. If the pressure in the heating system drops below 0.5 bar, an emergency situation arises and can cause shutdown or damage to the gas boiler.

The highest pressure value in the system is up to 3, less frequently up to 4 bar. For a five-story building, pressure values up to 5 bar are set, for a ten-story building up to 7 bar. It is necessary to keep the difference in pressure between the outgoing and return pipes. The difference should be 0,3-0,5 bars. After starting the heating check whether this is the case.

How to check the pressure in the boiler and the circuit

The pressure in the system is monitored by means of instruments that measure and reflect the pressure in the circuit by means of a digital or mechanical pointer dial. The pressure gauges are installed by the manufacturer at the outlet of the boiler.

When the system is installed, pressure gauges are also installed near the manifolds which distribute the heating medium to the various parts or floors of the building.

Why the pressure in the gas boiler drops or rises: the causes of jumps and regulatory values

Safety gauges for boilers in heating systems help control the temperature and pressure in the circuit, protect the equipment from collapse by venting excess pressure outside

Additional pressure control is required when using water heating boilers, under floor heating systems. A drop or rise in pressure  can be observed differently in different parts of the heating system.

Why the pressure in the gas boiler drops or rises: the causes of jumps and regulatory values

The closed circuit allows a higher pressure in the system, which increases its safety as the higher pressure increases the boiling point of the liquid

When starting the gas boiler, check the pressure gauge reading while the heating water is still cold - the pressure must not be below the minimum value indicated by the red adjustable gauge hand. The adjustment is performed by the representative of the company with which the service and gas supply contract is concluded.

The initial adjustment is performed at the first start of heating. Thereafter, the pressure is checked every week and, if necessary, the system is topped up with water. Top up when the temperature of the heating medium is below 40 °C.

Causes of increased pressure in the gas boiler

Detecting an increased pressure in the gas boiler is helped by frequent water discharge through the pressure relief valve and by blocking the unit operation besides the pressure gauge values. Having detected high pressure, first of all, discharge excess air through the Maevsky cocks and turn off the boiler. There can be several reasons for malfunctions.

Why the pressure in the gas boiler drops or rises: the causes of jumps and regulatory values

The normal upper pressure value is provided by the system by discharging the excess heating medium through the safety valve to the drain

The increase of the pressure in the gas boiler can be caused by damage to the secondary heat exchanger partition, which serves both to insulate and increase the contact area between the two circuits - heating and hot water supply.

The secondary heat exchanger draws water from the heating circuit to prepare and supply DHW in a two-circuit boiler. Damage to the baffle causes water from the DHW circuit to squeeze into the heating system, increasing the pressure in the system.

Why the pressure in the gas boiler drops or rises: the causes of jumps and regulatory values

The secondary heat exchanger serves to serve the hot water system. The DHW water is heated as a result of contact with the heating circuit coolant. The system is protected from the mixing of the two circuits by a metal partition, damage to which leads to the exchange of fluids and disturbance of the normal pressure

Replacement of the heat exchanger will solve the problem. It is possible to make repairs yourself, but it is not advisable to do it, because interfering in the work of gas equipment requires knowledge and experience in this area. Besides, self-repair of boiler will deprive you of the right for warranty service.

Failure in the work of automatics of gas boiler or rumbled impeller of pump, which sucks the air also increases the pressure in the gas boiler. Equipment malfunctions that lead to violations of the normal pressure can be as a consequence of a factory defect, breakdown of the control board, improperly configured system. Only a qualified master can eliminate this kind of problem.

Pressure increase in the heating circuit

What to do if the pressure in the heating system rises excessively?

First of all, the cause must be established, and there may be several:

  • Inadequate filling of the circuit, its air shortage. Due to rapid filling of the heating line airlocks may be formed in it. To avoid this phenomenon, fill slowly when starting the heating system.
  • The temperature in the circuit is too high. Any increase in temperature and coolant leads to its expansion and increases the pressure in the system. It is necessary to avoid too high an increase in order to protect the heating equipment from critical loads.
  • Stoppage of coolant flow.Causes may be blocked shut-off valves, clogged strainer, airlocks.

To locate the problem area, the whole circuit must be inspected step by step.

Why the pressure in the gas boiler drops or rises: the causes of jumps and regulatory values

The filter must be inspected and cleaned immediately after the boiler is started and then again after one week. Then it is checked and cleaned once a month or a season, depending on the degree of contamination of the heating medium

Losses can be caused by breakage of the make-up tap - wear of the valve gasket, mechanical damage of parts, scale caught between the seat and the gasket. If the valve leaks, the extra water coming from the water supply system into the heating system, increases the pressure in it, because the pressure in the pipeline HTW is always higher. It is necessary to tighten the tap or replace it if it is out of order.

Air congestion is a common cause of problems in the heating system. They can be caused by faults in the gas boiler itself, problems in the circuit or improper heating startup.

Restarting the system - its slow filling with coolant, starting from the lowest point, until water flows from the upper point of the circuit will help correct the problem. All air bleed valves must be open. A system that is not airtight can cause both increases and decreases in pressure.

Main causes of pressure decrease

Common reasons why the pressure in a gas heating boiler drops are:

  • Loss of heating fluid. Damage to the heating line leads to leakage, loss of heating water, and reduced head.
  • Cracks in the heat exchanger. Losses in the boiler itself will not only lead to a drop in pressure but can also provoke more serious damage to the equipment and damage the electronics.
  • Membrane rupture in the expansion tank.Liquid gets into the air compartment through damage in the rubber partition and the pressure in the circuit is reduced.

To determine where the system leaks, it is fed to normal pressure and the circulation pump is stopped. Step by step, the line must be inspected, the problem area must be identified and the problem must be repaired.

How the operation of the hydraulic accumulator affects the pressure

The problems with the expansion tank that affect the pressure in the heating circuit are very common. Incorrectly calculated expansion tank volume is one of the most typical causes.

Malfunctions can be caused by incorrect installation, low or high pressure in the tank air chamber, a damaged diaphragm - each cause can lead to a disturbed circulation of the heating medium in the system.

Extension tank: features and volume

If a small volume tank is installed in the heating system, it cannot compensate for the expansion of heating water when heated. At 85-95 °C, the water expands by approx. 4% and the excess volume flows out through a pressure relief valve.

For the expansomate to fully comply with its compensating function, a volume of at least 10% of the total circuit water volume must be available for systems with a gas boiler.

Why the pressure in the gas boiler drops or rises: the causes of jumps and regulatory values

If a larger volume tank is installed, the pressure variations will be even smaller. Reducing pressure variations has a positive effect on system operation and the life of the heating equipment

Damage of the tank membrane causes the water to fill its volume completely and the pressure in the circuit to drop. If you fill the volume of the circuit by opening the make-up tap, this creates a new problem - when the heating medium heats up it has nowhere to expand and the pressure in the system will increase more than normal. This can only be rectified by replacing the rubber partition.

Install the tank only on the return pipe, in front of the heating boiler. In this way the tank will have minimal influence on the operation of the circulation pump, which is installed after the gas boiler. In addition, the water temperature is lower here and the negative impact on the pressure in the system and on the tank membrane will be less.

Adjusting the pressure in the air chamber

The pressure generated in the expansomate air chamber can also cause the head inside the heating system to rise or fall. It is only possible to check and pump up the air in the tank when there is no coolant in the tank.

To do this, access to the common circuit must be shut off using the shut-off valve and the water must be drained through the drain. The pressure in the air chamber is then measured and pumped up/down to the required values.

Why the pressure in the gas boiler drops or rises: the causes of jumps and regulatory values

The pressure in the expansion tank may be checked with a car pressure gauge, pumped up with a car pump

The pressure in the air chamber must be 0.5 bar higher than the expected system pressure limit to adjust the pressure of the expansion tank. Once the pressure in the equalizing part of the tank is set, fill the circuit with cold water to the expected pressure value.

The air from the air chamber is then vented until the pressure in the heating circuit and the tank begin to decrease simultaneously - here the pressure in the system and in the expansion tank must be monitored simultaneously.

In this phase, changes in the values are little visible, so be prepared to immediately stop venting from the expansion tank as soon as you discover simultaneously For help, it is better to contact a technician from the gas service that supplies the blue fuel.

Are there any problems with pressure drop or rise during the operation of your gas boiler? Share the methods you have used to bring the pressure to normal values. Please leave your comments in the box below, here you can also ask questions and post pictures on the subject of the article.

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