Why Does My Boiler Keep Losing Pressure?
Boilers are designed to provide heat and hot water to a property through its radiators and taps. When a boiler loses pressure, it means the water pressure inside the central heating system has dropped below the level needed for it to operate properly. This can result in radiators taking longer to heat up, hot water issues, and in some cases, the boiler stopping altogether.
So, why does a boiler keep losing pressure? In this blog post, we’ll explore some of the most common causes, how serious the issue can be and when it may be time to consider replacing your combi boiler.
What pressure should a boiler be?
Most boilers should sit between 1 and 1.5 bar when the heating is off and around 2 bar when the heating is on. The measuring system essentially measures how much force the water has as it moves through pipes and radiators. The exact pressure a boiler should be can vary slightly depending on the boiler model.
How serious is boiler pressure loss?
The severity of boiler pressure loss depends on the issue, along with how significant the drop in pressure is. A small drop from time to time is not unusual, especially after bleeding radiators or colder months when heating is used more often. However, if the pressure consistently keeps dropping, it could be due to a leak, a faulty component or a more complex issue within the heating system. This could mean your boiler is becoming unreliable and could need replacing.
| Symptom | Severity | Recommended Action |
| Slight pressure drop every few months | Low | Repressurise the boiler and continue monitoring |
| Pressure drop after bleeding radiators | Low | Top up the pressure using the filling loop |
| Boiler pressure drops every few weeks | Moderate | Check for visible leaks and arrange a boiler inspection |
| Pressure drops daily | High | Contact a Gas Safe engineer as soon as possible |
| Boiler shuts down | High | Stop resetting the boiler repeatedly and book a repair |
| Water is leaking from pipes | High | Turn the heating off and seek professional repairs |
Most common reasons: Why does my boiler keep losing pressure?
There are a few reasons why your boiler may be losing pressure. Some reasons are more severe than others, but our expert team is here to help you identify the issue.
1. Water leaks in the heating
Leaks around radiators, pipework or valves are one of the most common causes of pressure loss. If you’re noticing damp patches, dripping water or unusual stains, it could be a sign of pressure loss. Homeowners should check for visible damage and contact an engineer if leaks continue.
2. Boiler losing pressure but no leaks
If your boiler is losing pressure but there are no visible leaks around radiators, pipes or valves, the problem may be caused by a faulty internal component. One of the most common causes is a damaged or waterlogged expansion vessel, which helps regulate pressure within the heating system. When the vessel is not working correctly, the pressure can rise when the heating is on and drop significantly when it cools down.
In some cases, the boiler may shut off or discharge water through the pressure relief valve. Having to frequently repressurise a boiler is a sign that the system should be inspected by a Gas Safe engineer.
3. The pressure relief valve needs attention
A faulty pressure relief valve can cause constant pressure loss, even when there are no visible leaks indoors. Common signs include water dripping from the overflow pipe outside and the boiler needing frequent repressurising. In this instance, it will require inspection from a qualified engineer.
4. Recently bled radiators
Bleeding radiators removes trapped air from the heating system, but it can also cause the boiler pressure to drop slightly. Immediate action is not usually required, but homeowners should monitor the pressure and repressurise the boiler if needed.
What to do if your boiler keeps losing pressure
Check the pressure gauge
Look at the boiler pressure gauge and confirm whether it has dropped below the recommended level, usually around 1 to 1.5 bar when the heating is off.
Inspect for visible leaks
Check around radiators, pipes and valves for signs of dripping water, damp patches or staining, as all of those could be signs of a leak.
Repressurise the boiler
Use the filling loop to carefully top the pressure back up to the manufacturer’s recommended level. Avoid overpressuring the system.
Contact a Gas Safe Engineer
If the pressure continues to drop regularly, or the boiler shuts down repeatedly, arrange a professional inspection to identify and repair the underlying issue.
Boiler pressure symptoms
The symptoms of boiler pressure loss can often provide clues about the underlying cause. Understanding what the pressure is doing can help determine whether the issue is a simple fix or requires professional attention.
| Symptom | Potential cause | Recommended Action |
| Pressure drops overnight | Small leak in the heating system | Check for visible leaks, arrange engineer inspection |
| Pressure rises when heating is on | Damaged or waterlogged expansion vessel | Contact a Gas Safe engineer to carry out repairs |
| Boiler needs repressuring every few weeks | Slow leak or deteriorating component | Book an inspection to identify the source of pressure loss |
| Water dripping from the overflow pipe outside | Faulty pressure relief valve or expansion vessel issue | Have the system inspected by a qualified engineer |
When should you replace a boiler that keeps losing pressure?
If your boiler only loses pressure occasionally, a repair is often all that’s needed. However, if you’re frequently repressuring the system, experiencing recurring faults or your boiler is over 10 to 15 years old, it may be more cost-effective to consider a replacement.
Intergas offers a range of combi boiler sizes, including 24kW, 25kW, 30kW, 32kW and 36kW models and annual boiler servicing that can help identify pressure-related issues before they escalate. Contact us for a combi boiler replacement.
FAQs: Boiler pressure problems
How can you check if your boiler pressure is low?
Check the pressure gauge on the front of your boiler. If the reading is below 1 bar, the pressure is likely too low. Most boilers operate best between 1 and 1.5 bar when cold.
Why is my boiler pressure high?
High boiler pressure is not normal and can place additional strain on the heating system. It is often caused by overfilling, a faulty filling loop or an issue with the expansion vessel.
How long should a boiler last?
Most modern boilers last between 10 and 15 years when properly maintained. If you’re wondering how long combi boilers last, lifespan depends on factors such as usage, servicing, and installation quality.
Can you still use a boiler with low pressure?
A boiler may continue working with slightly low pressure, but performance can be affected. If the pressure falls too far below 1 bar, the boiler may stop working altogether and require the boiler to be repressurised.
