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Last updated: 12th April, 2024


Boiler Losing Pressure, What Should You Do?

Boiler Losing Pressure, What Should You Do?

Key takeaways

  • Maintenance of proper boiler pressure ensures efficient heating and system durability.
  • Low boiler pressure can often be resolved by re-pressurising the system without professional help.
  • Preventing pressure loss extends system efficiency and can save on future repair costs.

If your boiler is losing pressure you should identify the cause as soon as possible.

Maintaining the correct pressure in a boiler is essential for efficient operation and longevity of the system. When a boiler loses pressure, it can impact how well your central heating system functions. Identifying and addressing the reasons for a drop in pressure are key to restoring your boiler's performance. It is generally a manageable issue that homeowners can often resolve without immediate professional intervention. 

Learning to troubleshoot and fix low boiler pressure not only enhances your system's efficiency but also conserves energy and reduces heating bills.

Initial signs of low boiler pressure may include radiators taking longer to heat up or not heating up fully. In some cases, the boiler may even switch off to safeguard itself.

It is crucial to regularly monitor the pressure gauge and be familiar with how to re-pressurise the system if needed. Regular maintenance, such as checking for visible leaks and ensuring the system is correctly pressurised, prevents future pressure loss and improves the boiler's lifespan.

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What is Boiler Pressure?

Boiler pressure is a measure of the force at which water circulates in a closed central heating system. The pressure is essential for the effective distribution of warmth throughout premises, ensuring hot water is readily available.

What should my boiler pressure be?

Typically, the boiler pressure for a domestic central heating system should sit between 1 and 1.5 bar when the system is cool (rising to 2-2.5 when it's hot). This is the optimal range to maintain effective circulation of hot water.

What is low boiler pressure?

Initial signs of low boiler pressure may include radiators taking longer to heat up or not heating up fully. In some cases, the boiler may even switch off to safeguard itself.

The standard pressure for a boiler when it is cold is usually around 1 to 1.5 bar, while when hot it typically rises to between 2 and 2.5 bar. It is crucial to regularly monitor the pressure gauge and be familiar with how to re-pressurize the system if needed.

Regular maintenance, such as checking for visible leaks and ensuring the system is correctly pressurized, prevents future pressure loss and improves the boiler's lifespan.

What is high boiler pressure?

Conversely, high boiler pressure happens when readings exceed 2 bar when the system is cold. While less common, this issue can strain the boiler's components and potentially lead to malfunctions.

Components of Boiler Pressure

  • Expansion Vessel: A device that absorbs excess water pressure.

  • Pressure Gauge: The indicator, typically a hydraulic gauge, that displays the current boiler pressure.

Significance of the Pressure Gauge

The pressure gauge, a critical component, allows for the monitoring of boiler pressure. It forms part of the boiler but can influence the whole central heating system. A correct reading is crucial for diagnosing issues with either low or high boiler pressure.

Common Causes of Pressure Loss

In boilers, pressure is paramount to maintain efficient water circulation throughout your home's heating system. A loss of pressure usually indicates an underlying issue which can variably impact the boiler's performance and, in some instances, shut down the system.

Leaks in the System

Leaks within the heating system are the predominant cause of boiler pressure loss. These can occur at numerous points:

  • Radiator Valves: Faulty valves can lead to gradual pressure loss.

  • Pipes: A leaking pipe, often hidden and undetected, compromises system integrity.

  • Soldered Joints: Over time, these joints may deteriorate, allowing water to seep out.

  • Leaking Radiators: Damaged radiators can contribute to noticeable pressure drops.

It is essential to inspect for damp patches or drips, both indicators of a leak.

Faulty Boiler Components

Malfunctions in boiler components can furthermore precipitate pressure loss. Important parts to assess include:

  • Pressure Relief Valve: Should this valve be stuck or damaged, it might leak water and reduce pressure.

  • Internal Seals and Valves: Perished or inadequately fitted seals and valves play a part in the pressure conundrum.

Periodic servicing can prevent or identify wear and tear on these crucial components, maintaining your boiler's pressure and operational efficacy.

Diagnosing Low Boiler Pressure

Low boiler pressure can be a common and frustrating issue for many homeowners. When a boiler loses pressure, it can affect the performance and efficiency of the heating system. Detecting the underlying causes early is crucial in maintaining a functional boiler.

Inspection of Pipework and Radiators

To identify the cause of low boiler pressure, one should first inspect the pipework and radiators for any signs of leaks. Leaks could manifest as damp spots on floors, hissing sounds from pipes, or visual drips. It is important to check all accessible pipes, especially those that are concealed or in low-visibility areas.

One should assess the state of the radiators as well, paying attention to joints and valves, including the expansion vessel’s Schraeder valve, which might require tightening to seal properly. Radiator bleed vents, which are different from Schraeder valves, should also be checked for proper operation.

Identifying Error Codes

Modern boilers display error codes that can provide insights into why a boiler is losing pressure. An owner’s manual or a quick consult with the manufacturer’s website may offer interpretations of these codes. Should a boiler persistently show an error code and lose pressure, it is advised to contact a Gas Safe registered engineer. Attempting to resolve these issues without proper knowledge or tools can be dangerous and may lead to further damage. A certified professional is equipped to conduct a thorough diagnosis and implement necessary repairs safely.

Step-By-Step Guide to Re-Pressurising Your Boiler

Re-pressurising a boiler is a straightforward procedure that entails locating the filling loop and operating the system’s valves. By correctly adjusting the water pressure, homeowners can often fix low boiler pressure themselves.

Locating the Filling Loop

The filling loop is typically a silver or grey flexible hose with a valve at each end and it's crucial for the task at hand. They will find this component beneath their boiler or within the boiler’s cupboard, and it is essential for introducing water into the system.

Operating Valves and the Pressure Gauge

Once they've located the filling loop, they should proceed with care:

  1. Turn off the boiler and ensure it has completely cooled down to avoid any injury or damage.

  2. Identify both valves on the filling loop; these need to be operated to allow water into the system.

  3. Their next step is to open both valves, starting with the one closest to the boiler, then the second valve. This should be done slowly to mitigate any potential risks.

They should watch the boiler’s pressure gauge and stop filling once the needle aligns with the recommended pressure level (usually between 1 and 1.5 bar cold and 2-2.5 hot).

Ensuring Correct Water Pressure

After water infusion, the pressure needs to be correct:

  • If the pressure exceeds 1.5 bar while they repressurise, they should bleed a radiator to reduce it.

  • Conversely, if the pressure is too low post-repressurisation, they would need to repeat the process, admitting more water into the system.

  • Once the desired pressure is achieved, close both valves firmly to prevent any leaks.

They should then restart the boiler and, if needed, hit the reset button. The boiler should now function with restored water pressure. If the pressure continues to drop frequently, it may indicate a leak or issue with a pressure relief valve, requiring professional assessment.

When to Seek Professional Help

In managing a boiler's pressure loss, one must discern when to apply a simple re-pressurising technique and when to involve a gas safe engineer. Attempting a DIY fix on complex issues can lead to further complications, warranting professional intervention.

Criteria for Hiring a Gas Safe Engineer

  • Disclosure of Gas Safe Registration: Verify that the engineer presents a valid Gas Safe identification card, confirming their legitimacy to work on gas appliances.

  • Track Record and Reviews: Prioritise local installers with a proven track record in repairing boiler leaks, supported by positive customer reviews.

  • Diagnosis and Cost Estimation: Choose professionals who provide a transparent diagnosis and upfront estimation of repair costs.

Should your boiler exhibit persistent pressure drops despite re-pressurisation attempts, sourcing a Gas Safe registered engineer becomes imperative. Continuous issues may signify a concealed leak or a critical malfunction needing expert diagnosis.

Risks of a DIY Fix

  • Compromise to Personal Safety: Incorrect handling of boiler components may lead to gas leaks, posing severe health and safety hazards.

  • Voiding Warranty: Unauthorised repairs might invalidate your boiler's warranty, leading to costly implications.

  • Escalation of Underlying Problems: Temporary fixes without addressing the root cause might result in recurrent failures and escalated repair costs.

When a boiler loses pressure recurrently after a DIY re-pressurisation, it signals the need for a professional evaluation. An engineer can pinpoint whether a simple sealant will suffice or if more extensive repairs are required. In cases of a boiler leak, an expert should always be consulted, as even minor leaks can elevate into more significant hazards.

Preventative Measures and Regular Maintenance

Ensuring the longevity and efficiency of a boiler hinges on regular maintenance and monitoring. A diligent approach to these practices is the cornerstone of preventing unexpected pressure drops and keeping the heating system in prime condition.

Monitoring and Adjusting Pressure Regularly

He or she must routinely inspect the pressure gauge to ensure the boiler water pressure remains within the optimal range, typically between 1 and 1.5 bar. Should the pressure fall beneath the requisite threshold, the homeowner is to manually reintroduce water via the filling loop until the gauge indicates proper levels. This not only curtails the risk of low pressure but also enables early detection of any irregularities.

Utilising Leak Sealants

When leaks are suspected, and the heating system is compromised, an effective short-term solution can be the application of leak sealant products such as Fernox F4. This sealant works by circulating within the system and sealing any leaks it encounters.

Although an auto air vent is typically installed to manage air within the system, adding Fernox F4 can offer additional assurance against pressure drops by addressing those less visible leaks.

Enhancing System Efficiency and Longevity

Maintaining a boiler's pressure is crucial for the system's efficiency and longevity. Properly serviced heating systems, including boilers and radiators, ensure reliable hot water and central heating performance.

Benefits of Regular Servicing

Regular servicing of a boiler, whether it be a combi boiler or a conventional model, extends its lifespan and maintains efficiency. Technicians check vital components, such as the pressure gauge, to certify that the system operates within optimal parameters.

  • Visual Inspection: Checking for any signs of leaks or corrosion.

  • Operational Tests: Ensuring all components are functioning correctly.

  • Pressure Adjustment: Balancing pressure levels to prevent strain on the system.

Addressing System-Wide Issues

It's not only the boiler that affects system pressure. Issues in radiators and pipework also contribute to inefficiencies. Radiators must be bled regularly to remove air pockets that compromise heating efficiency.

  • Leak Detection: A meticulous exam to locate any hidden leaks.

  • Component Replacement: Updating faulty parts, such as valve seals or the expansion vessel.

  • System Balancing: Adjusting water flow to radiators ensures even heat distribution throughout the property.

By addressing these system-wide issues, they can sustain consistent heating and mitigate frequent pressure drops.


Boiler pressure issues are common and typically indicate a leak in the heating system or the boiler itself. Identifying the source of the pressure loss should be the homeowner's priority. Leaks in the system often result from corroded pipes or faulty components and can sometimes be found visually or by using leak sealant products as a temporary measure.

Regular maintenance should not be underestimated, as it is crucial for ensuring that components within the boiler do not become loose or corroded over time. Repressurisation of the system is a simple process that can rectify the immediate problem of low pressure, but it is not a long-term solution if there is an underlying issue.

In cases where the problem persists or is unclear, contacting a professional is advisable. Certified engineers possess the expertise to diagnose and remedy boiler pressure problems effectively. Safety is paramount, and attempts to repair without the proper expertise can be hazardous.

Ultimately, understanding the causes of boiler pressure loss and the appropriate responses safeguards against prolonged damage and potential safety risks, ensuring a warm and comfortable environment within one’s home. Regular service appointments with a certified professional protect against unexpected issues and contribute to the longevity of the boiler system.

New Boiler Costs

Boilers can be a daunting purchase for many people as they’re an appliance with a lot of responsibility, providing heat for you and your family is something you want to get right. Boilers aren’t exactly a quickly disposable item either, potentially lasting you a decade.

Effectively, new boiler cost can be split into two segments: the first is the actual boiler itself (unit price), and the second is the cost of the boiler being installed (set up) in your property by an expert engineer. 

Here at iHeat, we want to remove all of this undue stress and make the decision making process of upgrading to a new central heating system, as easy as possible.

Boiler costs can vary depending on a number of factors including their brand, model, fuel, output, warranty, labour and installation type. Typically a new boiler will cost between £1,845 and £3,500, below is a list of average boiler installations offered by iHeat (guide only).

Installation Type

Price (inc VAT)

Combi to combi swap


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System to combi conversion


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New boiler install


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Back boiler to a combi


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System to system


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Frequently Asked Questions

Can a boiler lose pressure without a leak?

Yes, a boiler can lose pressure without a visible leak. This can be due to faulty pressure relief valves or other issues such as air ingress into the system. However, inspecting and identifying the root cause of the pressure loss is essential to address the problem effectively.

Why does my boiler lose pressure?

Boiler pressure may drop due to several reasons, such as a leak in the system, a faulty pressure relief valve, or incorrect boiler pressure settings. Identifying the cause is crucial to remedy the issue and maintaining the boiler's efficiency.

How to detect leaks causing pressure loss?

Detecting leaks can involve checking for regular dripping from the safety discharge pipe, and inspecting joints for flaking or bubbling paint, rust marks, swelling, or water stains on ceilings below the pipes. These signs indicate a possible leak affecting the boiler pressure.

How do I fix my boiler that keeps losing pressure?

To fix a boiler losing pressure, you may need to check for leaks, repair or replace the faulty pressure relief valve, or top up the system with water to increase the pressure. It is advisable to consult a professional engineer to accurately diagnose and repair the issue.

Is regular pressure drop normal?

While some minor fluctuations in boiler pressure may occur due to temperature changes, constant or significant drops in pressure are not normal and indicate a problem in the system. Such issues should be investigated and resolved promptly.

What are the steps to fix a low-pressure boiler?

To fix a low-pressure boiler, follow these steps:

  • Switch off the boiler and let it cool down.
  • Locate the filling loop and pressure gauge.
  • Open the filling loop valves to allow water into the system.
  • Close the valves when the pressure reaches between 1 and 1.5 bar.
  • Restart the boiler and check the pressure.

Please note that these are general steps, and specific instructions may vary depending on your boiler model. Refer to the manufacturer's guide or seek professional help if necessary.

How often should I check boiler pressure?

It is a good practice to check your boiler pressure at least once a month to ensure its efficiency and proper functioning. Regular checks help identify potential issues early and prevent more significant problems from occurring.

Can hot water affect boiler pressure?

Yes, hot water can affect boiler pressure. As the water heats up, it expands, increasing pressure. Similarly, as it cools down, the pressure decreases. Normal boiler pressure should be between 1 and 2 bar, and any fluctuations within this range are typical. However, if the pressure is consistently low or high, it may indicate an issue that needs attention.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.