Why Does My Boiler Pressure Keep Dropping?


At MML Plumbing, a trusted plumbing and boiler installation company in North London, we understand the importance of well-functioning central heating for a comfortable home. However, encountering problems like dropping boiler pressure can disrupt your daily routine. In this informative article, we address the common issue of low boiler pressure, and its potential causes, and offer solutions to help the boiler is losing pressure and slowly restore losing pressure and your central heating system’s efficiency.

The Significance of Boiler Pressure: Maintaining proper boiler pressure is essential for optimal functioning. Pressure dropping indicates a potential problem with either the boiler itself or its ventilation system. If you notice a recurring issue with boiler pressure, it is crucial to seek professional assistance.

Boiler Losing Pressure? Here’s Why and What You Need to Know

  1. System leaks: One frequent cause of boiler pressure loss is leaks within the central heating. Pipe wear and tear or freezing temperatures leading to burst pipes can contribute to leaks. To identify possible leaks, carefully inspect all pipes and fittings for signs of water damage or leaks.
  2. Faulty pressure relief valve: this valve can also result in low boiler pressure. This safety valve is designed to release excess pressure, but if it fails to function properly, the boiler can lose pressure through the valve. The valve will discharge the hot water externally, normally outside the property.
  3. Presence of air in the system: Air entering the system is another common culprit behind low boiler pressure. This can occur due to leaks or the need for bleeding, which involves removing air from the system. Seeking professional help is crucial to address air-related issues effectively.
  4. Defective expansion vessel: The expansion vessel is responsible for accommodating additional water generated when the boiler heats up. If this vessel is faulty, the boiler pressure can drop.

Auto Air Vent (AAV) Leak in Heating System

A properly functioning heating system is crucial for maintaining a comfortable and cosy home environment. However, issues can arise, such as leaks in the auto air vent, which can disrupt the efficiency of your heating system.

Auto air vents play a vital role in heating systems by automatically releasing excess air that accumulates in the system. This ensures efficient circulation of hot water and helps prevent airlocks.

Causes and Signs of Auto Air Vent Leaks:

  1. Wear and Tear: Over time, auto air vents may deteriorate due to regular usage, resulting in weakened seals or damaged components that can lead to leaks.
  2. Corrosion: Corrosion caused by the presence of oxygen or chemical reactions within the system can weaken the vent, causing it to develop leaks.
  3. High System Pressure: Excessive pressure within the heating system can put additional strain on the auto air vent, leading to leaks.

Signs that indicate potential leaks in the AAV include:

  • Hissing sounds near the vent or surrounding pipes.
  • Visible water stains, and dampness around the vent area.
  • Fluctuating system pressure.

Leaking Radiators, Towel Rails, and Radiator Valves

Leaking radiators, towel rails in most boilers, and radiator valves are common culprits of pressure loss in heating systems and can cause the boiler pressure to drop.

Over time, radiators can develop leaks due to corrosion, worn-out valves, or damaged pipes. These leaks can result in water loss, leading to a decrease in boiler pressure. It is crucial to address radiator leaks promptly to prevent further boiler pressure loss and potential damage to other boiler parts in the system.

Towel Rails: Towel rails, commonly found in bathrooms, are also prone to developing leaks. As with boiler parts and leaking radiators, water loss from towel rails can contribute to a reduction in boiler pressure.

Faulty Radiator Valves: these valves regulate the flow of hot water into the radiators. If the valves become faulty or worn out, they can fail to close properly, resulting in continuous water leakage. This constant leakage leads to pressure loss in the boiler.

Faulty Pressure Relief Valve on the Boiler

The safety valve is a critical safety component in central heating. Its purpose is to release excess pressure if it reaches unsafe levels. However, a faulty pressure relief valve can lead to pressure loss in the boiler. This can occur if the valve is stuck open, not closing properly, or if it’s damaged or worn out. It is important to call a professional gas-safe engineer and replace the lost pressure or relief valve to ensure the proper functioning and safety of the system.

Radiators Are Full of Air

Air trapped inside radiators can disrupt the proper functioning of your heating system. When radiators are full of air, they may not heat up evenly or produce sufficient warmth. This issue is commonly known as “airlock.” To resolve it, a process called “bleeding” is required. Recently bleed radiators involve releasing the air from the radiator by opening a radiator valve well, usually located at the top or side of the radiator, using a radiator key or a screwdriver. It is recommended to bleed radiators regularly or whenever you notice cold spots or inconsistent heating in your home. By doing so, you can restore optimal heating performance and efficiency to your radiators.

Damaged expansion vessel

The expansion vessel is an essential component of a boiler, responsible for accommodating the expansion of water as it heats up. However, if the expansion vessel becomes damaged or loses its pressure charge, it can result in pressure loss in the system. Signs of a damaged expansion vessel include fluctuations in boiler pressure, increased noise from the system, or water leaks. It is crucial to have a professional heating technician inspect and repair or replace the damaged expansion vessel to ensure proper system operation and prevent further pressure issues. Proper maintenance and periodic checks of the expansion vessel can help identify and address potential problems in a timely manner.

Recently bled radiators

If you have recently bled your radiators, it indicates that you have taken steps to release trapped air from the system. Bleeding radiators helps restore optimal heating performance and efficiency by allowing hot water to flow freely and evenly throughout the radiator. By releasing the trapped air, you should notice improved heat distribution and a more effective heating system overall. Regularly bleeding radiators, especially after maintenance or if you experience cold spots or inconsistent heating, is a recommended practice to maintain a well-functioning heating system.

The Pressure Gauge on Your Boiler is Faulty

The pressure gauge on your boiler plays a crucial role in indicating the correct pressure levels within the system. However, if the pressure gauge is faulty, it can provide inaccurate readings or fail to display any pressure at all. A faulty boiler to lose pressure gauge can make it difficult to monitor and maintain the proper pressure in your boiler.

To address this issue, it is advisable to have a professional technician inspect the conventional boiler and replace the faulty pressure gauge. They will ensure the installation of a new, reliable pressure gauge that accurately reflects the pressure levels within your boiler. By having a functional pressure gauge, you can monitor the pressure effectively and take appropriate measures to maintain the optimal operating conditions of your boiler.

Understanding boiler pressure a bit better

Boiler pressure refers to the amount of pressure inside a boiler, which is crucial for its proper operation. Understanding boiler pressure is essential for maintaining the efficiency and safety of the system. Here are some key points to grasp:

  1. Ideal Boiler Pressure Range: Most modern boilers operate within a recommended pressure range, typically between 1 and 1.5 bar. However, it’s important to consult your boiler’s manual or manufacturer’s guidelines for the specific pressure range recommended for your model.
  2. Monitoring Boiler Pressure: Boiler pressure can be monitored using a pressure gauge, usually located on the front panel of the boiler. The gauge displays the pressure reading in the bar, allowing you to keep an eye on the pressure level.
  3. Normal Boiler Pressure: The normal operating pressure for a boiler within the recommended range is typically around 1 bar. However, slight variations can occur depending on factors such as the size and type of the heating system.
  4. Low Boiler Pressure: If the boiler pressure drops below the recommended range, it is considered low pressure. Low boiler pressure can be caused by various factors, including system leaks, and bleeding radiators. It’s important to identify and address the underlying cause of low pressure promptly to ensure proper functioning.
  5. High Boiler Pressure: If the boiler pressure exceeds the recommended range, it is considered high pressure. High boiler pressure can lead to safety hazards, such as the risk of explosions or damage to the system. High pressure may be caused by issues like a defective pressure relief valve, a filling loop not properly closed, or a malfunctioning expansion vessel. Professional intervention is necessary to diagnose and rectify high-pressure issues.
  6. Adjusting Boiler Pressure: Some boilers have a filling loop, which is a valve or connection that allows you to increase the boiler pressure if it falls below the recommended level. However, adjusting the boiler pressure should be done cautiously and in accordance with the manufacturer’s instructions to avoid over-pressurization.
  7. Seeking Professional Assistance: It’s important to note that boiler pressure issues can be complex, and if you are unsure or unable to address them yourself, it is recommended to seek professional assistance from a qualified local gas engineer or plumber.

By understanding boiler pressure and regularly monitoring it, you as a boiler engineer can ensure the efficient and safe operation of your boiler system, promoting optimal heating performance and extending the lifespan of the equipment.

Fixing the boiler leak vs replacing your boiler

When faced with a boiler leak, homeowners often find themselves at a crossroads: should they opt for repairs or consider replacing the entire boiler system? At MML Plumbing, we understand the dilemma and offer professional guidance to help you make an informed decision.

In some cases, fixing the boiler leak through targeted repairs may be a cost-effective solution, especially if the leak is isolated and the boiler is otherwise in good condition. Our skilled technicians will assess the extent of the leak, determine the underlying cause, and provide efficient repairs to restore your boiler’s functionality.

However, there are instances where a new boiler or replacement becomes the more viable long-term option. If your boiler is old, inefficient, or has a history of recurring leaks, investing in a new boiler installation might offer greater benefits. A new boiler can provide improved energy efficiency, enhanced performance, and reduced risk of future leaks.

Our team will help you evaluate the condition of your current boiler, consider factors like energy savings, maintenance costs, and potential rebates, and guide you towards the most suitable solution for your needs.

Whether you require boiler leak repairs or a new boiler installation, MML Plumbing is here to provide reliable and professional service. Contact us today to discuss your options and find the best solution for your home heating system.

How to find a leak in a central heating system

At MML Plumbing, we specialize in providing professional and advanced central heating leak detection services. Our team utilizes cutting-edge methods, including acoustic, hydrogen gas trace leak detection, and thermal imaging camera equipment.

If you suspect a leak in your central heating system, don’t hesitate to contact us. Our experienced gas engineer will identify and locate the source of the leak, ensuring a prompt and effective resolution without any disturbance in your property. Give us a call today at 02083550840 to book a central heating leak detection service and regain the efficiency and reliability of your central heating system again.

Boiler Keeps Losing Pressure FAQs

There could be several reasons for your boiler to keep losing pressure, including system leaks, a broken boiler part, a faulty pressure relief valve, bleeding radiators, a damaged expansion vessel, or a faulty component.

Can boiler pressure drop without a leak?

Yes, boiler pressure can drop without a leak. There are other factors that can contribute to a drop in boiler pressure, besides boiler leaks, such as bleeding radiators, a faulty low-pressure or relief valve, or a damaged expansion vessel. It’s important to consider these possibilities when troubleshooting low boiler pressure.

How often should boiler pressure drop?

Boiler pressure should not drop regularly. Ideally, the boiler pressure should remain stable within the recommended range, unless there is a pressure rise for a specific reason such as bleeding radiators or releasing air from the system. If you notice frequent pressure rises or significant drops in boiler pressure, it indicates an underlying issue that requires professional attention.

Why does my boiler pressure drop every day?

If your boiler water pressure consistently drops every day, it suggests that there is a persistent issue within the system. Possible reasons for daily water pressure drops could include a significant leak in the system, a malfunctioning pressure relief valve, or a faulty component causing continuous water loss. It is crucial to have a professional heating technician inspect and diagnose the problem to identify the root cause and implement the necessary repairs to resolve the daily water pressure that drops.

Why is my combi boiler losing pressure but no leaks?

If your combi boiler is constantly losing pressure, but no visible leaks are apparent, there could be hidden factors contributing to the pressure loss. One possibility is an invisible leak, which could be located underneath the combi boiler casing in the floor or within the pipework, making it difficult to detect without professional assistance. These hidden leaks can gradually result in pressure loss over time.

Another potential cause for pressure loss without visible leaks is a faulty heat exchanger. The heat exchanger is responsible for transferring heat from the boiler to the water. If it malfunctions or develops internal leaks, it may be losing pressure slowly leading to pressure drops in the system. Diagnosing this faul requires the expertise of a professional heating engineer who can conduct a thorough examination and perform the necessary repairs or replacements.

It is crucial to involve a qualified heating engineer to inspect and address these potential issues when your combi boilers experience pressure loss without visible leaks. Their expertise and specialized equipment can help identify and resolve hidden leaks or faults within the boiler heats the heat exchanger, restore lost pressure and the proper functioning of your combi boiler.

What causes a boiler to lose pressure?

Possible causes of a boiler losing pressure include system leaks, damaged boiler losing pressure, relief valve, bleeding of radiators or the other underfloor heating and system, a broken boiler damaged expansion vessel, or an issue with the boiler itself.

Is low boiler pressure dangerous?

No, low boiler pressure is not inherently dangerous. However, it can indicate an underlying issue within the heating system that needs attention. It is important to address low boiler pressure promptly to ensure the optimal functioning of the system and prevent potential problems from arising.

Can a dripping tap cause boiler pressure to drop?

No, a dripping tap should not cause the boiler pressure to drop in a closed system. However, it is worth noting that if there is a crack in the copper pipe in the boiler’s heat exchanger, it can lead to pressure loss through the tap. In such cases, it is recommended to have a professional heating engineer inspect the leaking pipe and address the issue of loss of pressure and ensure the proper functioning of the boiler.

What should your boiler’s pressure gauge read?

The ideal pressure reading on a boiler’s pressure gauge should typically be within the range of 1 to 1.5 bar. However, it is important to consult your boiler’s manual or manufacturer’s guidelines for the specific recommended pressure range for your particular model, as it may vary.

Boiler Pressure Rising to 3 Bar How to Release Pressure From Boiler

High boiler pressure reaching 3 bar is a cause for concern. It is considered too much pressure or dangerously high and can lead to potential safety hazards or damage to the boiler system. It is essential to address this issue immediately by contacting a professional heating engineer to diagnose and rectify the underlying problem and fix the low boiler pressure. Do not attempt to fix low boiler pressure release the pressure yourself.

To release pressure from a full boiler that is losing pressure that has risen by dropping pressure to 3 bar, follow these steps:

  1. Locate the boiler’s pressure relief valve, usually found on the top or side of the boiler.
  2. Slowly open the valve by turning it counterclockwise. This will release some of the built-up pressure.
  3. Use a container or towel to catch any water that may be discharged from the valve during the pressure release.
  4. Monitor the pressure gauge on the boiler while releasing the pressure. Once the pressure drops to a safe level, typically around 1-1.5 bar, close the valve by turning it clockwise.
  5. If the pressure continues to rise or if you’re unsure about the process, it’s recommended to contact a professional heating engineer for assistance.


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