March 2, 2024

How to Lower Boiler Pressure: A Comprehensive Guide

Boiler pressure plays a crucial role in the efficient functioning of a boiler system. If the pressure is too high, it can lead to potential safety hazards and damage to the boiler. On the other hand, low pressure can result in inadequate heating and reduced efficiency. In this article, we will explore various methods to lower boiler pressure effectively and safely.

Understanding Boiler Pressure

Before we delve into the methods of reducing boiler pressure, it is essential to understand what boiler pressure is and why it is important. Boiler pressure refers to the force exerted by the steam or water inside the boiler vessel. It is measured in units of pressure, such as pounds per square inch (psi) or bar.

Boiler pressure is typically maintained within a specific range to ensure optimal performance. The ideal pressure range for most residential boilers is between 1 and 1.5 bar (14.5 – 21.7 psi). However, the specific pressure requirements may vary depending on the type and model of the boiler.

Reasons for High Boiler Pressure

High boiler pressure can be caused by various factors, including:

  • Malfunctioning pressure relief valve
  • Issues with the expansion vessel
  • Blockages in the system
  • Faulty pressure gauge
  • Overfilling of the system

Identifying the underlying cause of high boiler pressure is crucial to effectively lower it. Let’s explore some methods to reduce boiler pressure:

Method 1: Bleeding Radiators

One of the simplest and most common methods to lower boiler pressure is by bleeding the radiators. Over time, air can accumulate in the heating system, causing an increase in pressure. Bleeding the radiators releases this trapped air, reducing the overall pressure in the system.

To bleed a radiator, follow these steps:

  1. Turn off the heating system and allow the radiators to cool down.
  2. Locate the bleed valve on each radiator. It is usually located at the top or side of the radiator.
  3. Place a towel or container beneath the bleed valve to catch any water that may escape.
  4. Using a radiator key or a flat screwdriver, slowly turn the bleed valve anticlockwise. You should hear a hissing sound as the trapped air escapes.
  5. Once water starts to flow steadily from the bleed valve, close it by turning it clockwise.
  6. Repeat this process for all the radiators in your heating system.

Bleeding the radiators should help reduce the boiler pressure. However, if the pressure remains high, you may need to explore other methods.

Method 2: Releasing Pressure Through the Pressure Relief Valve

If bleeding the radiators does not lower the boiler pressure, the next step is to release pressure through the pressure relief valve. The pressure relief valve is a safety feature designed to prevent excessive pressure buildup in the boiler.

To release pressure through the relief valve, follow these steps:

  1. Locate the pressure relief valve on your boiler. It is usually located on the side or at the top of the boiler.
  2. Place a container beneath the valve to catch any water that may be released.
  3. Slowly lift the valve lever or turn the valve knob anticlockwise. This will release some water and reduce the pressure in the boiler.
  4. Once the pressure has dropped to the desired level, close the valve by pushing the lever back down or turning the knob clockwise.

It is important to note that if the pressure relief valve needs to be released frequently, it may indicate an underlying issue with the boiler system. In such cases, it is advisable to seek professional assistance to diagnose and fix the problem.

Method 3: Checking and Adjusting the Expansion Vessel

The expansion vessel is another critical component of a boiler system that helps regulate pressure. It absorbs the expansion of water as it heats up, preventing excessive pressure buildup. If the expansion vessel is faulty or not set to the correct pressure, it can lead to high boiler pressure.

To check and adjust the expansion vessel, follow these steps:

  1. Turn off the boiler and allow it to cool down.
  2. Locate the expansion vessel, which is usually attached to the boiler or nearby pipework.
  3. Check the pressure gauge on the expansion vessel. It should indicate the correct pressure range, typically between 1 and 1.5 bar.
  4. If the pressure is too high or too low, you may need to adjust it. Consult the manufacturer’s instructions or seek professional guidance for the specific procedure to adjust the expansion vessel pressure.

Properly maintaining and adjusting the expansion vessel can help ensure the boiler operates within the desired pressure range.

Method 4: Clearing Blockages in the System

Blockages in the heating system can disrupt the flow of water, leading to increased pressure. Identifying and clearing these blockages can help lower the boiler pressure.

To clear blockages in the system, consider the following steps:

  1. Inspect the pipes and radiators for any visible signs of blockages, such as debris or sludge.
  2. If you notice any blockages, you can try flushing the system to remove the debris. Flushing involves draining the system and running clean water through it to dislodge any obstructions.
  3. Consult a professional heating engineer for assistance with flushing the system or clearing more complex blockages.

Regular maintenance and cleaning of the heating system can help prevent blockages and maintain optimal boiler performance.

Method 5: Seeking Professional Assistance

If you have tried the above methods and are still unable to lower the boiler pressure, it is advisable to seek professional assistance. A qualified heating engineer will have the expertise and knowledge to diagnose and resolve any underlying issues with your boiler system.

Remember, attempting to fix complex boiler problems without the necessary skills and experience can be dangerous and may cause further damage. It is always better to rely on professionals for intricate boiler repairs.


Lowering boiler pressure is crucial for maintaining the safety and efficiency of your boiler system. By bleeding radiators, releasing pressure through the relief valve, checking and adjusting the expansion vessel, clearing blockages, and seeking professional assistance when needed, you can effectively lower boiler pressure and ensure optimal performance.


Avatar for Radhe Gupta

Radhe Gupta

Hello, I am Radhe. I am absolutely in love with writing and by working with News Whizz, I have developed a passion for it. It helps me to stay updated and know what is happening around the globe.

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