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Last updated: 31st July, 2023


Boiler Losing Pressure, What Should You Do?

Boiler Losing Pressure, What Should You Do?

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

If you've got a boiler losing pressure, you must check every possible issue before trying to fix the problem.

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Identifying the cause is almost as important as noticing the low-pressure boiler in the first place, especially when deciding if you need to contact an engineer for advice.

What Causes a Boiler to Lose Pressure?

Low boiler pressure can be caused by two major problems, which occur in different ways.

The first involves a water leak somewhere in the pipework: if left unchecked and unidentified, a leak can reduce the overall pressure of the water, as well as wear down the pipe and let extra air into the system.

In worst-case scenarios, this might even result in a pipe starting to wear down faster, making the leaks bigger and causing more water to be wasted.

This could even flow down onto other parts of the system or unrelated areas of your home, damaging key parts of your radiators or central heating system.

The boiler is the other common cause of pressure loss. If there are no leaks from your boiler, and none of the other appliances is faulty, then your boiler may be too old, broken or damaged to move water through a certain pipe properly.

Thankfully, there are ways to fix this, but it varies depending on the sort of boilers you have installed.

Is Low Boiler Pressure Dangerous?

Low pressure, on its own, won't usually be dangerous, unlike high pressure. However, if your boiler suddenly loses pressure at a rapid rate, it could be a sign that water is leaking out somewhere in your home.

This leak might damage electronics or break important appliances, and not having hot water can make it difficult to stay warm in cold weather.

Even if you aren't in danger, you'll need to pay for more fuel to get the same heat, no matter how good your radiators may be.

Why is My Central Heating Boiler Losing Pressure?

Central heating is one of the most important boiler uses in any home. Many people in the UK use a combi boiler because it is the cheapest and most accessible option - this generally means that it will be connected directly to the house's heating.

If you spot low pressure on boiler readings, you can immediately expect the heating to become less efficient.

If your pressure gauge doesn't find your boiler pressure low, then it's likely happening somewhere further in the system.

A leak in pipes further in the system, past the boiler, won't appear on your pressure gauge since it only checks a small section of your entire system.

If this happens, the issue isn't with the boiler and might be with a radiator (or multiple radiators) elsewhere in the house.

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What Should the Pressure be on a Boiler?

Different boiler models have different limits, but most boilers are designed to be around 1 and 2-bar units. If the boiler pressure is too high, you can use a pressure relief valve to try and reduce it, but you can't do the same with boiler low-pressure issues.

It might simply be a case of adjusting a certain valve to let more water through, filling the main pipe and increasing the amount of force it's putting on the system.

Always check your manual before you adjust this. Taking the pressure too high or low, even for a second, can waste fuel and might end up with you losing control entirely.

If you leave it as an excessive amount for too long, you could even destroy a large part of your heating system, especially if the boiler relies on the constant movement of water to function properly.

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

Restoring the pressure to your boiler isn't usually that tricky, and you don't need to call out an engineer unless it starts leaking or a valve becomes too faulty to use anymore.

As mentioned earlier, the pressure is generally directly related to the amount of water filling the system, which is why a leak will reduce it so much. The less air you have filling a radiator, its heating will be more efficient.

First of all, check the manual to get important deals about each valve, as well as figure out if you're using a combi boiler. Switch your boiler off completely, then attach a mains filling loop.

Open both major valves so that water can start leaking in - you're essentially flooding the system with water directly. Once you reach your desired pressure (around 1.5 bar, in most cases), close the valves and turn the boiler back on, resetting it if necessary.

Boiler Keeps Losing Pressure, Even After Being Re-Pressurised?

If the top-up didn't' fix your boiler pressure, something else is causing the pressure to leak out of the system instead. The more you lose, the bigger the air or water leak, so you must track it down quickly. These issues might include:

  • Water leaking out of some pipework in a key spot (repair or replace the pipe).

  • A pressure relief valve that's been left open (find and close it).

  • Bled radiators that have released air into the system (stop the bleeding, then wait a while for the pressure to flatten out).

  • Not enough water coming into the system (check to see if the mains are flowing into the system correctly).

  • The boiler is broken.

    In some cases, your entire system is just too worn out to keep working - this only really happens if you've had the same appliance for many years without proper maintenance or replacement parts, in that case, you will need a new boiler.

Should I Try and Fix Myself?

If you notice your boiler losing pressure and want to fix it quickly, it can be tempting to try handling the entire issue yourself. While it is not usually dangerous, you can still damage your boiler if you are not careful.

One person and some basic tools can repair a boiler losing pressure, but only if you know what you are supposed to be doing.

For example, if pressure drops because of a leaking pipe, you should ideally patch up the leaking pipe. But how do you do that, exactly?

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

Replacing a pipe can be just as complex since you must shut off the water, access the leaking pipe, remove it, find a replacement, fit it, and ensure everything is properly sealed.

That can be a lot of work for a single person, especially if you do not have any experience with boilers in the past.

If you can identify the problem and know how to fix it, then there is nothing wrong with trying to repair it yourself. However, remember that there are occasions when you won't know enough to make the changes yourself, and you might even cause more harm if you are not careful.

Get an Engineer

In cases where your boiler is suffering from pressure problems, you might have to get an engineer or specialist in to repair it for you.

There can be dozens of reasons why a boiler is losing pressure; not all of them are immediately obvious without taking the boiler unit apart. Of course, once you take it apart, you risk 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.

Sometimes, there are 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.

Keep in mind that it costs money to get an engineer out, so you will want to set some funds aside just in case. Even getting them to check the boiler might cost you extra, so it is not always the most affordable option for smaller problems.

Even so, it can be cheaper than replacing the entire boiler once it breaks down completely due to not being fixed.

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

More extreme types of damage are best left to a trained professional, and you should never try to fix something you do not understand or have the instructions for.

Error Codes for Losing Boiler Pressure

Certain electronic boiler models use error codes to tell you about major problems, such as a leak or sudden increase in the amount of air in the system.

These codes can help you track down problems before they become more significant and might even help you fix the system before it puts itself into a lockdown or shutdown mode.

Remember that not all codes will apply to all boiler models, and some might only appear under certain circumstances. Always look in your manual for this documentation to avoid making a mistake and try to solve the wrong problem.

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Viessman Boiler Codes:

  • Fault Code C1 = Differential air pressure.

  • Fault Codes B9, ED, F0, F-E5, F-EC, F-ED, F-EE, F-EF, F-FD, F-FF = Maximum pressure limiter issue.

  • Fault Code F5 = Faulty gas pressure switch.

  • Fault Codes EE and EF = Faulty air pressure switch.

  • Fault Code 0F = Service required.

Alpha Boiler Codes:

  • Fault Code 1 = General ignition failure.

  • Fault Code 2 = Low pressure in the primary system.

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

  • Fault Code 0A37 = Insufficient pressure and flow (switches the boiler off automatically).

  • Fault Code 0E37 - Insufficient system pressure.

Worcester Boiler Codes:

  • Fault Code E9 = Safety limiter.

  • Fault Code A1 = Dry pump.

  • Fault Code F0 = Major internal error.

  • Fault Code CE 207 = Low water pressure.

  • Fault Code H07 = Low water pressure that is impacting performance.

  • Fault Code 1065 B = Pressure sensor is defective.

  • Fault Code 1970 B = Sudden, rapid drop in pressure.

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.