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Boiler Leaking Water image

Why your boiler is leaking water and how to fix it

Author: Lee Devlin

Published on: 15/02/2021

A leaking boiler is not something that can be ignored as if left to develop further it could not only cause a lot of damage but become a serious health hazard. When spotted and dealt with quickly by a qualified Gas Safe engineer it will save you a lot of money and stress.

There are a number of reasons why a leak may develop in boiler, ranging from poor installation to age deterioration or too much pressure in the system. Whatever the reason for the leak the most important thing is to have your boiler repaired as soon as possible. We’ve put together a guide on how to identify a leak and what you can do next.

How do I know if my boiler’s leaking water?

If your boiler keeps cutting out due to low pressure, this could be because you have a leak that hasn’t yet been noticed. Sometimes you may see a boiler leaking water on the surface or wall below. Smaller leaks can also reveal themselves as a stain or mould close by to the boiler, or with warped skirting boards.

A boiler dripping from the bottom of the unit could be due to a faulty heat exchanger, or an internal leak yet to be identified. If you notice water coming out of a boiler you will need to contact an experienced company who can quickly attend your property to resolve the issue. Fixing a leak will also save you money in the long run as it ensures you are saving water – ignoring it will mean your water bills are likely to be higher.

Why is my boiler leaking water?

When a boiler is operating correctly you should not see any water leaking from the system. If you do, it could be because:

  • Water pressure is too high or low in the system.
  • The heat exchanger – that transforms cold water into hot water – has been damaged.
  • The joints that connect piping to the boiler may not have been sealed correctly upon installation.
  • You may have an old system that requires boiler servicing and repairs on some parts.

It is often the case that a leak can be fixed without the need for a new boiler, although this depends on the type and extent of leak that occurs.

Types of leaks: where is the leak coming from?

Water leaking from the bottom

Customers often ask: “My boiler is leaking water from the bottom, what can I do?” This could be caused by a leak from the heating pump, a faulty pressure release valve, heater exchange corrosion or issue with the auto-air vent.

Condensate pipe dripping 

A boiler condensate pipe dripping could be due to a cracked heat exchanger. This can lead to mains water or the system draining into the condensate pipe and the hot water can cause the pipe joints fail. Installing a new heat exchanger should resolve this.

Water dripping from Combi boiler overflow pipe

A boiler overflow pipe dripping from a Combi system (a pressure relief valve) is usually because there is too much pressure in the system, or the valve is not sealed correctly. A Gas Safe engineer can diagnose and fix a Combi boiler leaking in this way.         

Common causes of boilers leaking water

Leaking heat exchanger

This is common on budget or older boiler models. However, it isn’t something you will be able to diagnose yourself, so you will need a professional engineer to come and identify the issue.

A leaking heat exchanger could mean the end for a boiler, although there are occasions where it can be replaced. In many cases, it is more cost-effective to buy a new boiler instead.

High water pressure

Boilers start to struggle when they experience too much pressure, which leads to them breaking down. Check the pressure gauge on the boiler – anything over the 1 mark and the green bar will indicate there is a pressure issue.  

The easiest way to fix high water pressure is to bleed the radiators. Before starting, you should always ensure that the the filling loop taps under the boiler are closed. Then use a radiator key to bleed the radiators, turning it until water comes out to alleviate the pressure on the boiler. A tip here is to bleed the radiator that is at the highest point in your property – often a bathroom towel rail – as the air rises through the system and will often end up here.

Leaking boiler pipes

Corrosion of the pipes under the boiler is a common reason for a boiler leak. Sometimes it can also be due to poor installation, although the former is a more common occurrence. Check the pipes and if any are wet or leaking, if so, then this is the source of the problem.

A qualified gas engineer will have to be called out to fix leaking boiler pipes. But you can help contain the water in the meantime by placing a bowl underneath to capture it so it doesn’t run across the surface below.

Leaks from internal parts of boilers

Some leaks can be easier to identify than others. Internal boiler leaks on joints and parts such as seals can be a result of decay due to sustained pressure on the system. When seals are broken, water can start to come out quite rapidly.

You can remove the cover of the boiler to check this – if you are comfortable doing so. Alternatively, call out an engineer who will be able to spot this very quickly. It’s usually relatively easy to fix and seals do not cost a lot of money to replace.

How to check leaks caused by poor installation

You won’t necessarily know that the leak is being caused by poor installation – unless you are a qualified engineer. However, boiler pipes leaking can be a tell-tale sign that the boiler may not have been installed up to the required standard.

This will be something that only a qualified Gas Safe engineer will be able to fix. It may be the case that a new boiler installation is required to rectify the existing issues. This may be more costly than you hoped, but it will ensure you and your family are safe.

Is it an emergency?

Whenever you spot or believe a leak is occurring within your boiler you should contact an experienced Gas Safe engineer. No matter how small it may appear to be, the leak can eventually lead to extensive damage occurring not only to the boiler but to your property too.

Often, leaks do have fairly straight forward fixes and many people will fill comfortable bleeding a radiator. However, if the diagonses of what’s causing the leak is incorrect, the attempted fix could make things worse. If in any doubt at all, please do contact either the company that installed your boiler system or experienced Gas Safe engineers like ourselves.

Common leaking boilers (with error codes)

Worcester Bosch boilers

Error codes: A1, E9, CE207 and H07

These error codes will typically appear on models such as Worcester CDi Highflow, Worcester Greenstar 25i, Worcester CDi Class, Worcester Greenstar 30i and almost all Worcester boilers.

Vaillant boilers

Error codes: F.13, F.22, F.24, F.73, S.41 and S.53

These error codes will be seen on Vaillant EcoTEC Pro, Vaillant EcoMax Pro and Vaillant EcoTEC Plus models.

BAXI boilers

Error codes: 117, 118, 125, E78, H.02, H.03, H.04, H.05, H.06

These error codes will appear on Baxi 200 / 400 Combi Gas boilers.

What do I do if I have a boiler leaking gas or oil?

By design, a boiler should never leak gas or oil. If you see dripping oil or suspect there may be a gas leak it must always be treated as an emergency. A gas leak could emit carbon monoxide into your home, and is completely odourless, which is why it’s important to install a carbon monoxide detector nearby (landlords must install these by law in their rented properties). The intake of too much carbon monoxide can prove lethal.

If you start feeling sick, tired, dizzy or develop a headache, you should open all the windows in the property, extinguish any naked flames and leave as quickly as possible.

When it comes to leaking oil the smell may alert you to the problem and you may also spot stains or pooling on nearby surfaces. If this happens, close the tank’s tap or valve, open all the windows and place a container beneath the leak to prevent it from spreading.

Should your boiler start to leak gas or oil we advise you to get in touch with Homecure right away. We provide a range of boiler services including leak detection in London. We will aim to be at your address within the hour and our Gas Safe engineers will quickly locate the leak and ensure it is safely managed and repaired.

FAQs about boilers leaking water

Is a boiler leaking water dangerous?

Many customers ask “Is a leaking boiler an emergency?” and as qualified Gas Safe engineers, it is an issue we believe needs to be addressed as quickly as possible. It can significantly damage the boiler and your home, leading to rust and mould which can then spread.

Will a boiler leaking water mean it loses pressure?

If you see water dripping from boiler parts it will eventually lead to low water pressure. This will also affect your central heating, as the performance levels will be reduced and it will have to work much harder to heat the space.

Can I use my boiler if it’s leaking?

Another common question we hear is: “If my boiler is leaking can I still use it?” If you see a leak or notice the boiler pressure has dropped quite a lot then avoid using the boiler. Switch off the water supply and central heating and call the Homecure team as soon as possible.

Why is water dripping from my boiler overflow pipe?

A gas boiler leaking water from the overflow pipe could be because too much pressure has built up in the system due to a failed expansion vessel. You will need to call out a qualified Gas Safe engineer as soon as possible to have this fixed.

Is my boiler leaking carbon monoxide?

If a boiler is leaking carbon monoxide the flame will be yellow instead of blue. Condensation can also build on windows and/or staining around gas appliances. A boiler gas leak is extremely dangerous so in this instance turn off the boiler, open windows, leave the property and call a Gas Safe engineer immediately.


Meet the author, Lee Devlin

Published on: 15/02/2021

Lee Devlin is the managing director of Homecure Plumbers, London's favourite local plumbing service. Since 2009, Lee's been leading a large team of gas safe plumbing and heating engineers as well as growing a successful business built on quality customer service and workmanship, in a competitive industry within the Capital. He's been in the game for a long time, so he regularly shares his knowledge and experience with the public. His expert tips have been featured in lots of well known publications such as: The Sun, Metro, Insider, Homes And Gardens, Country Living and more!

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