How to Repair Low Boiler Pressure and Its Origins

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What Is Included in This Article?

Identifying the cause is almost as important as noticing the low-pressure boiler in the first place, especially when deciding whether to seek advice from an engineer.

Low boiler pressure can be caused by two major issues, each of which manifests itself differently.

The first is a water leak somewhere in the pipework: if left unchecked and unidentified, a leak can reduce overall water pressure while also wearing down the pipe and allowing extra air into the system.

In worst-case scenarios, this could cause a pipe to wear down faster, causing leaks to grow larger and more water to be wasted.

This could even spill over into other parts of the system or unrelated areas of your home, causing major damage to your radiators or central heating system.

The boiler is another common source of pressure loss. If your boiler has no leaks and none of the other appliances are broken, your boiler may simply be too old, broken, or damaged to move water through a specific pipe properly.

Fortunately, there are solutions, but they vary depending on the type of boilers you have installed.

Is it dangerous to have a low boiler pressure?

In contrast to high pressure, low pressure is rarely dangerous on its own. However, if your boiler suddenly loses pressure, it could indicate that water is leaking somewhere in your home.

This leak could damage electronics or break important appliances, and not having hot water can make staying warm in cold weather difficult.

Even if you are not in danger, you will have to pay more fuel to get the same amount of heat, regardless of how good your radiators are.

What is causing my central heating boiler to lose pressure?

One of the most important applications of a boiler in any home is central heating. Many people in the UK use a combi boiler because it is the cheapest and most accessible option; in most cases, this means that it will be connected directly to the house's heating system.

If you notice low pressure on boiler readings, the heating will become less efficient almost immediately.

If your pressure gauge does not show that your boiler pressure is low, the problem is most likely occurring somewhere else in the system.

Because your pressure gauge only checks a small section of your entire system, a leak in pipes further in the system, past the boiler, will not be detected.

If this is happening, the problem isn't with the boiler, but rather with a radiator (or multiple radiators) somewhere else in the house.

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How Much Pressure Should a Boiler Have?

The limits of various boiler models vary, but most boilers are designed to be between 1 and 2 bar units. If the boiler pressure is too high, you can try to reduce it with a pressure relief valve, but you can't do the same with boiler low-pressure issues.

It could simply be a matter of adjusting a valve to allow more water through, filling the main pipe and increasing the amount of force applied to the system.

Before making any changes like this, always consult your owner's manual. Taking the pressure too high or too low, even for a second, can waste fuel and result in you losing control completely.

If you leave it in an excessive amount for too long, you may end up destroying a large part of your heating system, especially if the boiler relies on constant water movement to function properly.

How to Re-pressurize (Top-Up) Your Boiler

Restoring pressure to your boiler is usually not difficult, and you won't need to call an engineer unless it begins to leak or a valve becomes too faulty to use.

As previously stated, pressure is generally proportional to the amount of water in the system, which is why a leak will significantly reduce it. The less air that fills a radiator, the more efficient its heating.

First and foremost, make sure you read the manual to learn important information about each valve and to determine whether or not you have a combi boiler. Turn off your boiler completely, then connect a filling loop from the mains.

Open both major valves to allow water to enter the system - you're essentially flooding the system with water. Once you've reached your desired pressure (roughly 1 bar), 5 bar), close the valves, and restart the boiler, resetting it if necessary.

Even after being re-pressurized, the boiler continues to lose pressure.

If the top-up did not restore your boiler pressure, something else is causing the pressure to escape the system. The more you lose, the larger the air or water leak, so you'll need to find it quickly. These problems could include:

  • Water leaking from a pipe in a critical location (repair or replace the pipe)

  • A pressure relief valve that has been left open (locate and shut it)

  • Bleed radiators that have let air into the system (stop bleeding, then wait for the pressure to settle).

  • Inadequate water entering the system (check to see if the mains are properly flowing into the system)

  • The boiler has failed.

    In some cases, your entire system is simply too worn out to function - this only occurs if you've had the same appliance for many years without proper maintenance or replacement parts; in this case, you'll need a new boiler.

Should I Try to Repair Myself?

If you notice your boiler losing pressure and need to fix it quickly, it can be tempting to try to handle the entire problem yourself. While it is not usually dangerous, if you are not careful, you could end up damaging your boiler.

A boiler that is losing pressure can be repaired by one person with basic tools, but only if you know what you're doing.

For example, if pressure is dropping due to a leaking pipe, you should ideally patch up the leaking pipe. But how exactly do you do that?

You can sometimes seal the crack with clean rags and tape, but depending on the pressure level, this can eventually wear down or become too weak to keep the water in.

Replacing a pipe can be just as difficult because you must turn off the water, gain access to the leaking pipe, remove it, find a replacement, fit it, and ensure that everything is properly sealed.

That can be a lot of work for a single person, especially if you've never worked with a boiler before.

There is nothing wrong with attempting to repair the problem yourself if you can identify it and know how to fix it. However, keep in mind that there will be times when you will not know enough to make the necessary changes, and you may even cause more harm if you are not careful.

Recruit an Engineer

If your boiler is experiencing pressure issues, you may need to call in an engineer or specialist to repair it.

There could be dozens of reasons why a boiler is losing pressure, and not all of them are obvious without disassembling the boiler unit. Of course, taking it apart exposes you to the risk of losing pieces or damaging something.

For things like a small leaking pipe, you can usually fix it yourself, but an engineer might be able to identify why that pipe, in particular, was the one that got damaged

Outside causes of leaks that do not appear immediately, such as corrosion-causing leaks or a bending pipe that is more likely to wear down faster, can occur.

Keep in mind that getting an engineer out there costs money, so put some money aside just in case. Even having them check the boiler may cost you extra, so it is not always the most cost-effective option for minor issues.

Even so, it may be less expensive than replacing the entire boiler if it fails completely due to not being repaired.

On the other hand, there are many cases where a boiler issue cannot be fixed by someone who is not properly trained, particularly with gas boilers, which can be dangerous if handled incorrectly.

More severe types of damage are best left to a trained professional, and you should never attempt to repair something that you do not understand or for which you do not have the instructions.

Error Codes for Boiler Pressure Loss

Certain electronic boiler models employ error codes to alert you to major issues, such as a leak or an unexpected increase in the amount of air in the system.

Using these codes can assist you in identifying problems before they become more serious, and may even assist you in repairing the system before it enters a lockdown or shutdown mode.

Keep in mind that not all codes will apply to all boiler models, and some may only appear in certain situations. Always look in your manual for this documentation to avoid making a mistake and attempting to solve the wrong problem.

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Codes for Viessman Boilers:

  • C1 = Differential air pressure fault code

  • B9, ED, F0, F-E5, F-EC, F-ED, F-EE, F-EF, F-FD, F-FF = Maximum pressure limiter problem

  • Fault Code F5 indicates a faulty gas pressure switch.

  • EE and EF fault codes indicate a faulty air pressure switch.

  • Fault Code 0F indicates that service is required.

Codes for Alpha Boilers:

  • General ignition failure (Fault Code 1)

  • Fault Code 2 = Low primary system pressure

  • Incorrect system pressure, air in the pump = Fault Code 61

  • Fault Code 0A37 = Insufficient pressure and flow (automatic shutdown of the boiler)

  • 0E37 Fault Code - Insufficient system pressure

Codes for Worcester Boilers:

  • E9 = Safety limiter Fault Code

  • A1 fault code = Dry pump

  • Fault Code F0 denotes a major internal error.

  • Low water pressure = Fault Code CE 207

  • Fault Code H07 = Inadequate water pressure affecting performance

  • Fault Code 1065 B = Defective pressure sensor

  • 1970 B = Sudden, rapid pressure drop

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