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Boiler leaking water? – Causes & how to fix a leaking boiler

How to fix a boiler leaking water guide & what to do next

Is your boiler leaking? An unexplained pool of water is never a good discovery in your home. And when it’s right underneath your boiler, then that’s probably not a good start to the day. However, there is a whole heap of reasons as to why this might have happened.

Is your boiler leaking? - Question Mark

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So turn off the water supply to your boiler, mop up the water because you don’t want any accidents, and let’s then go through some of the reasons why it might be happening and what you can do about it.

In this guide, we will discuss why your boiler is leaking, and how to fix it.

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How frequently do people have boiler leaking problems?

One of the most frequent issues with central heating is a leaky boiler. A leaking boiler will not only leave pools of water for you to clean up but will also result in significant pressure changes.

Save money - when your boiler is leaking

Your entire central heating system may be harmed by these. Our team recommends that if your old boiler leaks, you should look to install a new boiler, you can compare new boiler quotes here.

As well as due to the age of some boilers if they are older than 10 years, they often do rust and become weaker. If your old boiler is not covered by a plan, compare boiler plan covers here.

Why is water leaking from my boiler?

A modern gas boiler is what’s called a sealed combustion chamber. That means that water should not be able to escape from the heating system. So, if your boiler is leaking, then that’s a sure sign of problems, and there are several reasons why this might be happening.

Do bear in mind that you’ll probably have to call out some gas-safe registered engineers to carry out an inspection. That’s because they’re the only professionals who are legally allowed to take the boiler casing off and work out what’s going on.

is a boiler leak dangerous - hazard sign

When a boiler is leaking water, it’s a potentially dangerous situation so that’s even more reason why you need a correctly qualified gas-safe engineer to get it fixed.

The boiler pressure is too high

Your boiler needs a delicate balance between the air and water within the heating system to operate correctly. If your boiler’s pressure is too high then the pressure relief valve kicks in. Then you get the leaking water as a way to reduce the excess pressure and get the level back down to a safe point.

This valve is also known as the pressure release valve, so you may see it referred to like this within your boiler manual. Your boiler might also be fitted with a temperature control valve that closely monitors the water temperature and prevents it from getting too high.

To check if the boiler pressure is too high, take a look at the pressure gauge on the front of the boiler. If the pressure exceeds 2 bar, then it’s going to be too high. To prevent any further damage and fix the leaking boiler issue, that extra pressure needs to be released.

Reducing high boiler pressure

So you need to get the boiler pressure down to between 1 and 2 bar. This is simply done by bleeding the radiators while keeping an eye on the pressure gauge.

Low boiler pressure can also cause problems, so it’s important not to let too much out as well. You’ll know if low pressure is a problem by your radiators not heating as they should and also through checking the pressure gauge on the boiler.

If your boiler creates too much pressure or even loses pressure regularly, then it’s a sure sign of something else not working as it should.

Damaged seals

Boilers have water running through them and the central heating system 24 hours a day, 365 days a year. With this constant flow or even just the presence of water, parts can begin to decay. Once a seal becomes damaged, then the result is a leaking boiler.

Fixing damaged seals

This is another job for your gas-safe registered engineer. That’s because they will need to go into the mechanics of the boiler to find the damaged seal and then replace it.

If the boiler is leaking water because of a minor sealant issue, then it can be a cheap fix. However, there are times though when corrosion has caused the problem and it might end up being more economical to begin looking for a new boiler quote.

Wear and tear

Even the best makes of boilers don’t last forever. Parts like the temperature sensors and temperature valve along with the boiler pump, can become faulty or just worn out due to wear and tear.

Ten years is considered to be a good working life for a boiler and heating system. If you’re at that ten-year point, then it might be time to consider a new boiler.

An old boiler is not only unreliable they are also much less efficient than modern boilers.


Most boiler leaks are the result of either corroded pipes or hot water cylinders. Over time they become brittle and that’s when the leaking boiler scenario comes in.

If you’re not sure where the leaking water is coming from, follow the boiler pipework and look for that telltale drip. Take a good look at the pipe fittings where there are joins and where they turn a corner as they tend to be key problem zones for water leak issues.

Fixing corrosion issues

If it’s just a small section of the boiler pipes that have become corroded, then it can probably be repaired. This doesn’t have to be undertaken by a gas-safe registered engineer if the problem pipe is outside of the boiler.

However, we strongly recommend ensuring that any boiler engineers that you call out are experienced. Otherwise, you might end up with a bigger problem on your hands!

If the corrosion had happened inside the boiler, then a new boiler installation might be the best option. Knowing that a brand new best boiler gets you out of the constant repair bills could be worth every penny.

It might well be cheaper than you think and new boiler installations can be started within a couple of days of the order being placed. Find out all your options with a new boiler quote.

Loose joints

We’ve already mentioned the need to check the joints for corrosion but it could be that it’s a loose joint that’s resulted in your boiler leaking water. As the pressure builds inside the heating system then it’s going to expose any weak points.

Fixing loose joints

This might be one that you can attempt yourself but make sure you tighten the joint the right way and don’t cause a spray of hot water to come flying out. If that’s even a remote possibility, then a heating engineer can come and fix that leaking boiler for you in minutes.

Faulty Installations

You would hope that a new boiler would mean that all the worries of any problems would disappear overnight. But, if you decided not to get a gas-safe engineer in to fit the heating system then a leaking boiler could be one of the outcomes.

Shoddy work resulting in poorly fitting pipes and loose joints is going to lead to a leaking boiler. And this issue is completely avoidable when an experienced heating engineer completes the job.

Leaking or faulty heat exchanger

The heat exchanger is one of the key components of your boiler. It takes the heat from the hot gas and then uses it to heat the cold water. It’s not too unusual for them to crack or become damaged boilers reaching the end of their working life and it can be a common problem with budget boilers.

Fixing a damaged heat exchanger

This is one of those issues that you’re not going to be able to diagnose until the boiler case is off, so again the job of a qualified engineer. Unfortunately, it is an expensive repair so do balance up the cost of getting the boiler working again, with that of a new boiler cost.

What about gas leaks?

If your boiler is leaking gas then you need to take immediate action. A gas leak can be incredibly dangerous and leaking gas has the potential to quite literally take your house down.

Advice from the National Grid on a suspected gas leak is:

If you smell leaking gas:

1. Don’t light matches or smoke

2. Don’t turn electric switches on or off

3. Open all of the doors and windows

4. Turn off the gas meter at the control handle, unless the meter is in the cellar, then leave it alone

5. Call 0800 111 999 – the Gas Emergency Services

Do also make sure that you fit a carbon monoxide detector in your home. Fumes from this gas are odourless so you have no idea you have a problem until it might be too late.

Boiler leaking oil

If you can see your boiler leaking oil or you spot oil stains under your boiler it needs immediate attention from a heating engineer. While not generally dangerous on its own, if there is any risk of the oil being near a flame, then the results can be catastrophic.

If the oil tank is leaking, then Government’s advice is to, first of all, prevent the oil from soaking into the ground or going down drains and then to contact a UK spill-accredited clean-up company.

Is my boiler leaking dangerous?

Although a boiler leaking water is not as serious as a gas leak, it could be an indication of a bigger problem. If that’s not promptly repaired, then the boiler leak could go on to cause other problems.

These include short-circuiting of the electrical components, rusting, and damage to flooring and the boiler’s immediate surroundings.

So, rather than being dangerous, a boiler leaking water is more likely to be a huge inconvenience and hassle than you could do without!

Boilers are a little like cars, when one thing goes in older boilers, then there can be others just waiting to break down at the most inconvenient time.

Should I turn my boiler off when it’s leaking?

A leaking boiler should be turned off even though it isn’t blatantly harmful to do so in order to reduce the risk of your electrics short-circuiting and to stop released water from ruining your flooring, fixtures, and furnishings.

Check out our Boiler Service Guide to learn more about your boiler and to understand when you should consider having it serviced.

You should always hire a Gas Safe licenced professional rather than attempting to fix a leaky boiler yourself.

Can I fix a leaking boiler?

fix a boiler leak - tools

So, as we’re already mentioned there are a few repairs that you could undertake yourself and then there are those that need the attention of a qualified engineer. A boiler leaking water that requires the casing to be removed to identify the issue, needs a gas-safe engineer.

gas safe registered

Finding the true cause of the water leak from the boiler system may not be simple. If a leaking boiler is ignored, it leads to mildew and fungal growth, causing structural damage to your home. To perform a thorough assessment and any necessary repairs, contact a Gas Safe Registered Engineer.

If you are not qualified, you should never attempt to fix your boiler yourself; instead, call a heating specialist.

If my boiler is leaking, can I still use it?

Dealing with a leaky boiler is a dirty process that can also prove to be costly. Keeping your boiler in good condition is crucial to preventing leaks and the damage and disruption that leaking water causes.

On your list of “how to prevent a boiler leaking” precautions, a yearly boiler servicing by a qualified gas professional should be first. Since it will guarantee that your boiler and heating system are operating safely. You can identify any possible problems before they result in leaks. Long-term savings include time, money, and stress when potential water leaks, corrosion, or damaged parts are discovered early.

Boiler leak sealant – Boiler leaking water from the pipe

If you’ve found a tiny boiler leakage in the pipes, then you might be able to fix the water leak using a boiler leak sealant. This is added to the heating system and forms a boiler leak seal across any tiny holes in the pipework.

The problem is, it acts as a sticky plaster. So, even if it appears that you have completed the boiler repair, the hole remains. And over time, the sealant will break down and then the pipe will begin to leak water once again.

Is your Boiler leaking, when the gas is turned off?

This is due to expansion and contraction. When the boiler is hot and has gas, the leak closes. When it is cold, the split opens and allows water to drip out. It is not particularly harmful; rather, the drip needs care and may require a new boiler. It is most likely safe unless it drips into electrical parts. It is best to have it checked out because ultimately the boiler will be harmed.

The diverter valve might also be to blame. Either the diaphragm has been ruptured. Hire someone who is gas-safe registered to change it.

How to prevent my boiler from leaking?

One of the critical factors in preventing a leaking boiler is in good maintenance. That means having a heating engineer perform an annual service and resolving any minor issues as soon as possible.

Many minor problems with your boiler can quickly escalate and result in a boiler leak, so as tempting as it might be to ignore them, you mustn’t do.

Also, consider investing in a magnetic boiler filter. These assist in preventing debris accumulation in the pipes, which could lead to increased pressure on the pipework. That, in turn, can cause a boiler leak, especially on older pipes.

A magnetic filter can also help improve the efficiency of your boiler. That’s because it does not have to work as hard to force the hot water around the heating system. As well as through all of that sludge and debris.

In turn, your heating bills will be lower because the boiler doesn’t need to use as much energy to do its job.

Is it time for a new heating system?

If you’re finding yourself calling out a gas engineer regularly then it is time to consider a new boiler. Not only are modern boilers more efficient you’ll also be able to relax without worrying. Especially about how much the next boiler repair is going to cost.

If you’re wondering which boiler is the right one for you we have several guides to help you come to a decision.

From the cost of a new boiler in our Viessmann boiler prices article. And our in-depth guide on individual boilers such as our Worcester Bosch 8000 review. We can help you find the perfect boiler for your home.

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