When your boiler’s pressure is too high: 6 tips for lowering it


As soon as you notice that your boiler’s pressure is too high, you should rectify it immediately. There are many reasons why boiler pressure can rise above the normal 2 bar level. However, sometimes it can rise much higher than this and rise above 3 bars (the area where your boiler’s pressure gauge starts to turn red). In these cases, you should find a solution quickly and you start off by turning the unit off. Today, we will discuss some of the causes for elevated pressure, and we will also give you some tips on how to lower your boiler’s pressure.

How to lower your boiler’s pressure when it is too high

Below are some great tips on how to reduce your boiler’s pressure when it is already too high.

Turn your boiler off and contact a technician immediately

This should be your first step, especially if you don’t know much about boilers. If you try and fix the problem yourself without having much knowledge, you might make it worse, and it could even be dangerous. In contrast, qualified professionals not only have the necessary tools, but they also have the vital experience to notice your boiler’s symptoms, to diagnose what is wrong with it, and to fix it in the best possible way.

Check the flue pipe or chimney

Obviously, any appliance that burns fuel needs to expel the residual fumes resulting from the combustion process. Domestic boilers are no exception. Each boiler has a smoke outlet, and some expel the gases directly outside, while others are connected to an individual or shared chimney that expels them.

Currently, the new regulations stipulate that boilers must be watertight or condensing, and when it comes to fume output, it means that gases are forced out via a turbine, and not because they are less dense than air at room temperature. This means that a chimney of fume outlet should be straight and horizontal.


This advanced fume expulsion technology doesn’t necessarily mean that the units can’t break down or become congested. Sometimes pressure rises excessively because of a large obstruction in the chimney or fume outlet pipe. This can be because of normal dirt or because a foreign object or animal has managed to enter the pipe.

A well-functioning boiler typically expels smoke that is colorless. If it is not doing this, there are problems. Signs that it is congested or damaged or that the flue pipe is generating too much pressure in the boiler normally include:

  • The smoke coming out has a color, whether it is black, gray, or white. Any of these colors indicate that there is dirt or congestion (or poor combustion in the burner due to failure or incorrect regulation). A little bit of color is not serious, but if it is an intense color, this is a bad sign.
  • Expelled smoke, even though it is colorless, has a bad odor of some kind, caused by congested chemicals or organic waste.
  • There is no smoke at all coming out from the chimney or gas outlet. It is absolutely impossible that an appliance that functions by burning fuel doesn’t emit fumes of some kind into the outside air.
  • Fumes are accumulating in unusual places in the boiler. This is a sign that the smoke is unable to exit through the end of the chimney or gas outlet, and it is therefore searching for other exits. Smoke helps the boiler to get rid of both gases and excess temperature as a result of its operation. Any obstruction in the gas outlet will cause the temperature and pressure to rise.

Of course, when it comes to boilers that have forced air intake and expulsion through ventilation, in some cases the turbine that takes in and expels air from the boiler might be broken. You should ensure that the turbine is working properly before you start to clean or replace the chimney or gas outlet.

If you need more details about this, you can read the relevant articles on the Suner blog. Here is the link to them. If you need spare parts for chimneys or gas outlet pipes, you can obtain them by using this link to our store.

Check the boiler’s water inlet and outlet pipes well

If the pressure rises to over 3 bars, this is considered as abnormally high pressure and it could be because water is continuously entering the boiler. The safety valve will probably give you a warning by spontaneously expelling water to decrease the pressure (unless it is faulty). If the expansion vessel is not broken and is operating normally, there should not be any excess pressure.

However, if you notice that the pressure is increasingly rising even though the boiler is off, this is because the inlet valve is probably open or faulty. When water continuously enters a closed circuit such as a heating circuit, the pressure will increasingly rise. Possible solutions for this problem are:

  • Close the inlet valve
  • Clean the inlet tap if it has been calcified by water
  • Replace it with a new part
  • Open the outlet valve

If you need replacements for these parts, obtain them from the Suner store via the following links:

Ensure that the plate exchanger is not connected to the circuit

The exchanger is an important part of the mechanism that transmits the heat generated by the burner directly to the water. This means that is plays a vital role in the system’s pressure levels. The heat from the exchanger increases the water temperature that will circulate through the heating and DHW circuits.

The exchanger is a sensitive part and consists of metal plates that are connected by a gasket. The plates form passages that are interconnected. It is through these passages that the water circulates and heats up. If the heat exchanger plate fails (meaning the gaskets separating the plates are not performing their function and allow the plates to touch each other) this can result in your boiler’s pressure rising.

If your heat exchanger plate is broken, you can rely on Suner for a great replacement. We are attaching a link here so that you can check the heat exchanger plates we have for sale. We only supply genuine products of the highest quality.



Bleed your radiators at least once a year

Radiators are at the opposite end of the heating system from boilers. They are the hot water’s final destination and provide a comfortable temperature for your home, which is why they are located as far as possible away from the boiler.

The area between the boiler and radiators provides many points through which air can enter the heating circuit (even if it is a closed circuit), and congest the radiators. Water is the so-called “heat carrier” or “transportation” of heat from the boiler to the various rooms, and air doesn’t help the process but hinders it.

A frequently asked question related to this is: Why does my boiler’s pressure rise with the heating system? It is normal for this to happen because while the domestic hot water system (DHW) is an open circuit and its pressure is not a problem, the heating circuit is, by contrast closed and is what directly affects the boiler’s internal pressure.

Any congestion in the closed heating circuit means a pressure rise, while will be reflected on your boiler’s pressure gauge. Additionally, if this pressure increase is related to radiator congestion, then your radiators might make noises when you turn on the heating.

The solution for this is to ensure that your radiators are always working optimally, which involves periodic bleeding. You can conduct a preliminary test by bleeding the radiator closest to the boiler. If this solution works, bleed the other radiators as well. If you don’t know how to bleed radiators, here is a link to an article explaining the step-by-step process.

In addition, if you notice that your radiators need spare parts (drains, caps, panels, etc), you can rely on your Suner store to provide you with everything you need. Click on the following link for access to all the radiator spares for sale in our store:



Don’t forget to service your boiler regularly

The law states that boilers should be serviced at least once a year. This prevents most of the problems and risks of having a boiler in the home, including elevated pressure problems. It is possible that some pressure problems are simply due to dirty parts, congested or closed circuits that need replacing, and similar issues that can be avoided or resolved by regularly servicing your unit. These problems often cause elevated pressure in Junkers boilers, but they can affect any boiler brands.


2 simple tips for keeping your boiler’s pressure under control

In addition to the general advice we have seen so far, we can also recommend some preventative measures. If you keep an eye on the boiler pressure every day (or at least often), this will avoid panicking and alarm. Here are the tips:

  • Use the boiler for a short while even in summer. Don’t leave your unit off for too long, even if winter is far away. If it is summer or the weather is warm and you are not going to use your boiler for a few months, you should at least switch it on from time to time to maintain it. You can follow this method: turn on your boiler for at least 10 minutes and at least 3 times during the entire period that the unit is idle. This will prevent the pressure from rising too much when you start using it intensely again.
  • Check the pressure gauge often. Don’t forget to check the pressure gauge at least once a week. This will prevent any nasty surprises with excess pressure levels. If you check it on a weekly basis and you notice that it is a bit high, you can always regulate it or adjust it accordingly. Keeping the pressure regulated can extend the life of your unit and save you unnecessary costs on expensive parts or help prevent having to buy a whole new unit.

Suner is your trusted partner for boiler spare parts

We have a wide range of spare parts for popular brand boilers and burners, especially wall-mounted boilers. The main wall-mounted boiler brands include: Ferroli, Saunier Duval, Vaillant, Roca, Beretta, Immergas, Junkers, and more.

We also stock Siemens, Honeywell, Dungs, Suntec and Danfoss spare parts for popular boilers such as Riello, Elco and Weishaupt. You will always find what you need with us. Click on the following link to find over 30,000 genuine boiler spare parts:


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