August 21, 2023

Why Does My Boiler Keep Losing Pressure?

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Boilers are one of the must-have items in residential and commercial properties. Boilers are meant to provide heat and hot water for the occupants. A boiler is one of the different parts of a heating system, including a pipe network, blowers, and radiators. The primary function of the boiler is to produce hot water.

The hot water then runs through the pipework to the radiators installed in different building parts. This hot water is used to heat the living rooms and the workplaces of the building. It is also used to warm the water in washrooms and kitchens. The functioning of this entire system largely depends on the adequately maintained boiler pressure.

Boiler pressure plays a vital role in the supply of heated water to the pipe network. It works on a prescribed pressure. Any increase or decrease in the pressure causes malfunctioning of the boiler. Excessive pressure may leak water, whereas low pressure disrupts the hot water supply. Decreased boiler pressure may make you awkward, especially when it happens while you shower.

Boiler Pressure – Basics

When we talk about a boiler, the most commonly discussed topic is boiler pressure. A boiler produces hot water that needs to be circulated throughout the building via a pipe network connected to the boiler and heating system. The boiler pressure is a measurement of the pressure with which the hot water circulates through the heating system of the building.

So, it's the pressure that enables the circulation of hot water through the heating system. Any change in the pressure will therefore impact the hot water supply, ultimately affecting the heating of rooms and the warm water supply to the washrooms and kitchens.

Workable Boiler Pressure

Usually, a boiler comes with a gauge fitted on it. Traditionally, the pressure gauge used in the boilers is of the analog type, with a needle moving around a round pad with pressure bars mentioned on it. However, now the boilers also come with a digital pressure gauge that displays the current pressure digitally.

This pressure gauge's purpose is to give users an instant status of the water pressure in a boiler. But the question is how you would know whether the pressure is normal. Generally, the boiler pressure between 0.7 to 2.5 bars is considered the normal pressure range for smooth working of the boilers. However, most boiler engineers recommend the safest range between 1 to 1.5 bars.

Hence anything below 1.0 bars will be considered low pressure. If it further drops below 0.7 bars, it's a case of extremely low pressure. Similarly, if it crosses the 1.5 mark, it is an indication that the pressure is increasing. But when it crosses the 2.5 mark, it is an indication that the boiler pressure is now in the danger zone. So, keep an eye on the pressure gauge; it shouldn’t drop below 0.7 and must not, in any case, go beyond the danger level of 2.5.

Where to Find a Pressure Gauge on your Boiler

Most boilers come with an analog pressure gauge shaped like a round meter with a needle. This meter often has a white, green, and red pressure range marked on it. It helps to know whether the pressure is normal or abnormal instantly. If the needle is in the green area, it indicates normal pressure. If it drops below the green, the pressure will be considered low. And when it enters the red zone, it is an alarm that the pressure has entered the danger zone.

This gauge was usually fitted beneath the boiler body alongside the pipe network in old boilers. But the new models, especially the combi boilers, are right in the front, just below the main control panel. However, it may vary with the brands and models of the boilers. You may consult the user manual book to find the exact location of the pressure gauge.

You must be aware of the location of the pressure gauge on your boiler so that you can instantly check the pressure.

Indications that your Boiler’s Pressure is Low

When your boiler faces low pressure, the immediate signs might be:

  • Drop in room temperature. That means the heating system is not working correctly.
  • No warm water in your washroom or kitchen.
  • Radiators are not warming, as they must be if everything works perfectly.
  • If one or all of the above indications are observed, you must immediately check the pressure gauge. If the pressure has dropped below the green zone and entered in the white, it means the pressure has dropped significantly, and immediate action is required to bring it to the regular or green zone.

Indications That your Boiler’s Pressure is High

You may come across another abnormality in the performance of your boiler associated with the boiler pressure. It is a high boiler pressure that may also affect the performance of a boiler. The immediate signs of high boiler pressure might be:

  • Suddenly, the boiler is shut down.
  • There might be some water leaks.
  • You need to check the pressure gauge in case of any such event. In high pressure, the needle would be in the red zone. If that's the case, immediate action is required to relieve the pressure. Otherwise, it may result in a mishap.

Usually, it happens when you try to increase the boiler pressure and accidentally let too much water in the boiler. It often happens when you forgot to close the water inlet valve properly. So, always be vigilant enough while working with boiler valves.

Impact of Low and High Boiler Pressure

While high boiler pressure is considered dangerous, low pressure is not a risky event. The high pressure may result in water leakage from various external or internal parts of the boiler. If left unattended and pressure increases, the boiler may blast, causing colossal damage.

But the low pressure has no such potential threats. The only impact will be a disruption in the warm water supply in the washrooms and kitchens and a lack of heating in the living areas. Well, one might think it is quite a significant threat, especially in the extreme cold season. But rest assured, low boiler pressure will not cause any physical damage to you or your property.

Reasons Why a Boiler Loses Pressure

There might be various reasons behind the loss of pressure in your boiler. The main reasons for such an incident might be:

Excessive Bleeding of Radiators

In case of high boiler pressure, you must bleed the radiators to reduce the pressure within the permissible limits. But if you bleed too much, the boiler pressure may drop considerably. Similarly, excessive air release may also result in a pressure drop.

This can be managed easily on your own. The only thing you need to do is to re-pressurize the boiler. First, locate the filling point of the boiler. You will find two taps with a copper pipe. To do the re-pressurizing task, first, connect the copper pipe between the two taps. Open one tap to let the water in. Simultaneously, keep watching the pressure gauge. When the needle starts rising, open the second tap. Keep the taps open until the pressure reaches between the permissible ranges of 1.0 to 1.5.

Leakage in the Boiler

The main reason for pressure drop in a boiler is water leakage in the boiler itself. Water may start leaking from any internal or external part of the boiler, such as the diverter valves, heat exchangers, rings, washers, and air vents. It may be due to any loosening or corrosion in various internal parts due to consistent usage over the years.

If left unattended, minor leakages may result in progressive pressure loss, whereas a significant leak can instantly drop the boiler pressure.

Leakage in the boiler is a serious issue. You need to get it checked by a qualified and professional boiler engineer. Usually, minor leakages can be stopped, but big leakages may require the replacement of the damaged part. Yes, it may cost you a bit more, but it is always wise to replace the damaged part. Even the smallest leak cannot be left unattended. It may affect the overall performance of your boiler system.

Leakage in the Heating System

The pipe network is the main area where you can expect a leakage outside the boiler. The pipe runs along the entire building. Hot water circulates in this network from the boiler to the endpoints and back to the boiler. The continuous flow of hot water may result in corrosion or damage to pipes, which results in water leaking out from the damaged parts of the system.

Water may also leak from the bends or joints and any loose connections. Whatever may be the reason for the water leakage from the piping network, it lowers the boiler pressure. While the leaking water may often be visible, sometimes it remains hidden if the pipes are concealed. Whatever may the case, leakage of water from the pipe network needs your immediate attention.

Get the services of a professional engineer to resolve the problem. Otherwise, it may cause severe damage to your property, apart from repeated boiler pressure dropping. Remember, it's a technical job, so never try it yourself.

Expansion Vessel Damage

A damaged expansion vessel can also result in a considerable drop in boiler pressure, but it's a complex event. Firstly, the boiler pressure tends to rise drastically and even may go up to 3.00 bars in case of a damaged expansion vessel. Since the expanded water cannot go anywhere, when the vessel is damaged, it increases the boiler pressure.

The auto safety system is triggered when the pressure enters the danger zone. It results in the opening a pressure relief valve that lets the water out of the vessel. It releases too much pressure rapidly, which results in a sudden drop in boiler pressure to a considerably low level.

To avoid such an event, the damaged expansion vessel might need comprehensive repair work or even the replacement of the vessel. Re-adjustment of vessel pressure may also be needed. Being a highly sensitive and technical task, you must get it done by a well-experienced and qualified boiler engineer.

Fault in the Pressure Relief Valve

Pressure relief valves are meant to release the excessive pressure build-up in the boilers. Generally, these are set to be activated automatically if the pressure crosses well beyond the safe limits. So usually, the pressure relief valve should ideally start releasing the pressure when it crosses the 3.0 range.

But any fault in the pressure relief valve may leak water from the system even at a lower pressure. Consistent leakage due to a faulty pressure relief valve will result in repeated drops in the boiler's pressure. The water leakage in this case, should be visible on the copper pipe in the shape of dripping. Again you cannot resolve this issue on your own. Call a professional boiler engineer to resolve this issue. But don't let it go unattended.

Boiler Parts Might be Broken

If boiler parts are broken, it may also result in a pressure drop. In such an event, it might be difficult for you to locate the fault instantly. So, you have to engage a qualified boiler engineer to detect the fault. The only solution to this problem is to get the broken parts replaced. You cannot do it yourself, so hire the services of an engineer to resolve this issue.


  • Never try to fix the boiler issues on your own, especially when replacing the parts is needed. Do get the services of a qualified engineer to resolve such issues.
  • Repeated replacement of parts may be costly in some cases. It might be a considerably costly affair if your boiler is too old and you need to replace various parts. Think about replacing the entire unit instead.
  • If there are no visible signs of water leakage or broken parts, you should try to re-pressurize the boiler. But if the problem persists, you must call the boiler engineer.


Low pressure in a boiler is quite a common issue, especially with old boilers. It results in a drop in the room temperature, which means the boiler cannot provide sufficient hot water to heat the building. Another problem will be in the shape of no warm water in washrooms and kitchens.

Both situations are very compromising, especially in extremely cold weather conditions. So, you need to be able to identify why the boiler pressure keeps on dropping. There might be various reasons and possible solutions to avoid this unwanted situation. Regular servicing and maintenance of the entire boiler system is therefore necessary. Additionally, you must learn the basics of the boiler pressure phenomenon.

Most importantly, you need to get the faults removed by a qualified boiler engineer. Never try to play with different parts and controls on the boiler. It may damage your boiler.

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