Why is my boiler leaking water?

boiler leaking water

Are you asking yourself the following questions about water leaking or dripping from your boiler?

  • Is your boiler leaking water at the bottom?
  • Why is my boiler leaking water?
  • Is it dangerous to use your boiler if its leaking water?
  • My boiler is leaking water, does it need repairing?
  • How do I fix a leaking boiler?
  • Are internal parts of the boiler causing the leak?
  • Does the boiler need a heat exchanger replacement?

If the answer is yes, this guide on leaking boilers will point you in the right direction. Explore the questions below and be on your way to a fully operational central heating system in no time at all!

Safety first though, if your boiler is losing water, we advise you not to use the boiler and turn the stop tap off.

The stop tap is usually found under most kitchen sinks.

At this point, if you were covered under a boiler cover plan, you would simply call us and we would send out an engineer to fix your leaking boiler. Boiler cover can offer peace of mind all year round, for a range of issues, perhaps saving you from an unwanted new boiler cost.

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Do boilers leaking water often?

Boilers are fascinating pieces of machinery. Don’t laugh, it’s true.

We bet you didn’t know that there’s a place in the UK where boilers are more likely to break down. One study revealed boilers are most likely to break in London.

boiler leaking water

This is where the highest number of inquiries occur.

Do you live in Yorkshire? You’re in luck!

This is the area with the lowest chance of a boiler disaster.

It’s theorised that this is to do with the higher number of older homes in London. 

The same study also provided evidence that boilers tend to break at a certain point through the year. 

The majority break down in…January.

That’s right, in the middle of winter, at the exact time when you want your boiler to work. This is probably because your boiler is used more at this time. 

This is the exact reason we recommend to have your boilers annual service in the summer so you know that it is ready and working for winter.

So, now that you agree boilers are indeed fascinating, let’s move onto the questions you are asking yourself about leaks.

If you’ve stumbled upon this article, there’s a good chance you are already asking yourself, why is my boiler leaking water from underneath? Or Why is my boiler dripping water?

Unfortunately, this can mean you are due a new boiler replacement. If you’re lucky, you may just require a repair.

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7 Reasons your boiler is leaking water

1. Incorrect boiler pressure

boiler gauge

You might have heard about issues with boiler pressure before.

Don’t worry if you don’t entirely understand the concept of boiler pressure; not many people do. 

The main point to understand is simple.

Too much pressure will be bad news for your boiler and you.

The best Combi boilers are typically equipped to handle issues with high pressure. Most often, there’s a pressure release valve that will be used to get rid of excess water. If that isn’t working correctly, then internal parts will begin to fail, and this will cause the leak. 

How to check for high or excess pressure

boiler pressure

It’s simple to determine whether your combi boiler is operating with too much pressure.

To do this, you just need to make sure that you are looking at the gauge.

If it’s in the green, you’re fine.

If the boiler is going into red then the boiler pressure is too high.

This could have knock on effects on your central heating system and be causing the water leak from your boiler.

Read more: Boiler Pressure Too High or Low? A Fix-All Guide.

Can You Fix It?

You might be able to. You don’t always need to be a Gas Safe registered engineer.

  • First, make sure that the filling loop tap is closed.
  • There will be one or two black taps that you can quickly check yourself.
  • If you are unsure, turn them anticlockwise and you’ll see an increase in pressure.
  • The next step is to make sure that you are bleeding the boiler.
  • It’s here that your handy radiator bleeding key which you’ve probably never used in your life will become the ultimate tool.
  • Get a bowl to catch the water leaking as you loosen the nut on the end of the radiator. Do this for a few of your radiators to reduce the pressure of your boiler.

2. Expansion Vessel Failure

expansion tank

It is possible that the issue with your dripping boiler is due to a fault in the expansion tank.

This can be separate from the boiler or an internal part inside a boiler.

They can be quite difficult to replace, depending on the build of the boiler in question. 

If you have a Baxi boiler leaking, a Vaillant boiler leaking, Ideal boiler leaking or a Worcester Bosch boiler leaking from the bottom then if you have boiler cover or warranty you are in luck.

You shouldn’t have to pay a penny for them to come out and fix your boiler.

boiler brands

If the expansion tanks are inside the boiler, they will usually be flattened down to save on space.

Usually, the tanks are between 12 and 18 litres. 

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Is The Issue Common?

A problem with a leaking vessel tank is quite common and is typically due to rust or corrosion.

There is also the possibility that the tank will fail due to the butyl diaphragm which divides the two parts of the chamber.

Signs Of An Issue?

The main sign of an issue here can be noted by when the boiler leak occurs.

The leak might only start after the boiler burner has been on for quite some time.

If that’s the case, it’s almost guaranteed to be a problem with a faulty expansion tank. 

Temporary Fixes

How to stop my boiler from leaking? A Gas Safe heating engineer will be required to provide a full fix for this issue.

That said, you can give yourself a temporary solution. 

  • To do this you need to transform one of the radiators that you don’t need into an expansion tank.
  • This is quite tricky, but it’s possible by bleeding the radiator to create an air pocket at the top.
  • You need to bleed the radiator until it is half full before refilling the heating system and then bleeding out the air. 

As we said before it is technical and the best option will always be a proper fix by a Gas Safe heating engineer. 

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3. Corroded Pipes

You might find the boiler is leaking water from the pipes underneath your system. The boiler overflow pipe could be leaking if the pipes have corroded. 

  • It’s easy to spot this. If the pipes aren’t hot, you can feel them for the wet patch.
  • If they are, shine a torch across the pipes and you’ll see a droplet forming somewhere. This is the source of the leak.

Now, if the floor isn’t covered in water, your main concern might be, how much this is costing you. 

If you put a bowl under the leak – an ideal temporary solution – you’ll probably find the amount lost through a day barely covers the surface.

How Does This Happen?

boiler overflow pipe leaking

This is quite a common issue with older boilers.

Surprisingly, it’s a natural process.

Metallic debris will corrode the copper.

This is going to cause little gaps which is causing the boiler overflow dripping.

Hopefully, you only have one gap but you could have several. 

It’s also possible that the boiler is brand new. That might mean that the over flow pipes haven’t been installed correctly.

It’s possible this means that you have been provided with an awful boiler installation.

This issue is however, quite common and it’s often difficult to spot during the installation on most types of boilers.

Although, if you notify your provider and it is a new installation they should fix it immediately free of charge. 

Can You Fix It Yourself?

Is a leaking overflow pipe dangerous?

The answer is no, it is not dangerous to fix if you’re a trained Gas Safe engineer, you can definitely try fixing it.

However, if you don’t have the skill, it’s best to call in a professional to avoid further damage.

Do be aware that if your boiler is over ten years old, you will likely require a boiler replacement rather than a boiler repair.

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4. An Overworked, Worn Out Boiler 

Remember we mentioned that most boilers fail in winter? 

Well, this is when your boiler is under the most pressure. 

It’s likely that boilers like this are already on their last legs and the extra holiday weight pushes them over the edge. 

worn out boiler

Signs Of A Worn Out Boiler

One of the key signs of a boiler that needs to be put down is corrosion.

Corrosion is easy to spot, and if there’s lots of corrosion there’s going to be problems of your boiler leaking water from the bottom, boiler water coming from the underneath, boiler heat exchanger leak, boiler leaking outside from the overflow pipes and so on.

Is your boiler leaking water dangerous? It can be Yes. If it isn’t caught early enough, it could cause a flood and a lot of damage. A slow leak in your central heating system can be the start of a big problem.

How do i find a leak in my heating system?

First things first, look at the pipes, check different parts of the boiler, check there are no heat exchanger boiler problems and try to decide whether the boiler still looks as good as new.

If it doesn’t, then it’s time to consider whether you need to bring in a replacement boiler

It’s not all as bad as it sounds; it’s worth noting that corrosion isn’t always going to signal the end of the life of your central heating system. This is going to depend largely on the level of damage. 

Is It Salvageable?

Some boiler engineers will helpfully suggest that you attempt to fix your boiler leaking water problem.

When you are provided with this advice, it’s a simple maths problem. 

You need to decide whether it’s in your best interest financially to fix or replace.

In most cases replacing will be the best bet with corrosion. But there are rare situations when a repair could be worth the cost. 

At Boiler Central we offer different finance options if you do decide to go down the replacement route.

The issue with a repair is that the best you can do is put off the inevitable.

Eventually, an old boiler is always going to fail. So, if you’re approaching ten years, it’s time to say goodbye. Get a quote on a new one below:

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5. Internal Issues And Leaks 

It’s possible that your boiler is leaking on the inside!

You probably have already spotted the issue with this particular problem. You’re not going to be able to see it. 

However, inside your boiler, there are lots of different pieces.

Similar to blood vessels in the human body, these transfer fluids.

When there’s a leak, the situation can go south quite quickly. 

The seals inside the boiler can break over time and this is another issue you might run into if your boiler is over pressured. 

internal boiler issue

When the seals do fail, you’re going to lose water at a rapid pace.

Now, this issue can start to impact that heating bill.

Checking The Issue

If you are having issues with the seals, then they are not completely hidden. It is possible to remove the cover of the boiler.

Once you do this, you’ll be able to take a look. Do make sure that you are not touching the boiler. 

First, it’s probably going to be hot and second, tampering could lead to more damage. 

Can You Fix It?

You can’t, but a certified Gas Safe heating engineer certainly might be able to.

Hopefully, these repairs aren’t quite as expensive as you might assume.

Particularly, if it’s only a minor issue with the seal.

If on the other hand, there’s a larger problem such as a heat exchanger problem, then it could be worth getting a new boiler

That’s again, likely due to our old foe, corrosion. 

6. Issues With The Heat Exchanger 

boiler heat exchanger

You might find that you are having problems with the heat exchanger of your boiler.

If this is the case, then it’s important to be aware of a few things. 

First, this is easily the most expensive part of your boiler.

Second, they fail all the time. Unfortunately, this is usually a clear sign that you have bought a shoddy boiler. 

Spot The Signs 

Unfortunately unlike the seals, this is an issue that you definitely won’t be able to check yourself.

Although, there are a few signs that you might spot.:

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7. Loose Joints 

Finally, we’ll leave you with perhaps the best possibility for you financially. The joints of your boiler system may be going to get looser over time.

This is a common issue as your boiler ages. 

Why Does It Happen?

Again, this is a natural process where the water within the boiler expands when it is heated, and contracts during the cooling process.

How To Fix Loose Joints and Stop Boiler Leaking

To fix this, you need to understand what joints are loose.

You may struggle to recognise this yourself.

That’s why, ideally, you should seek out the support of a professional Gas Safe heating engineer. 

The good news is that this won’t be a costly repair.

Instead, it’s one of the easiest changes to make to a boiler.

It could still be a sign that a boiler needs a replacement. But, if you do opt for a repair, then it won’t break the bank.

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Should you repair a boiler which is leaking water?

Usually, with a boiler leaking water, it’s going to be a coin toss whether you need to repair or replace.

When you have a problem with a heat exchanger, the answer is simple. Replace and you’ll save yourself money in the long term. 

Even if you did choose to repair, there’s a good chance it will fail within the next few years regardless. 

Either that or the temperature valve may go or even the pressure relief valve.

While heat exchangers can be replaced, the cost just doesn’t make it worth it. You’re far better off purchasing a new boiler instead. 

When you do this, do make sure that you check the reviews.

This can help you avoid buying another boiler where the heat exchanger is going to fail after just a couple of years. 

Final Thoughts on Leaking Boiler Repair

One of the key concerns that you probably have is whether or not a boiler leaking water is a dangerous situation.

We’re pleased to say that in most cases, this won’t be an issue.

Some faults with boilers will cause ridiculously hot water to come out of your taps. 

Other than this, however, your main concern should be the cost.

Unfortunately, the longer you leave a leaking boiler, the more expensive a repair is likely to be.

That’s why you should make sure that you are calling in a professional to fix it without delay. 

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