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Why Is My Boiler Leaking Water?

A boiler that has water leaking from it requires the attention of a heating engineer as it could lead to more serious faults. Common causes of a boiler leaking can be corroded pipes, high pressure, and loose joints, or if your boiler was only recently installed the leak could be due to poor installation. If you discover even the smallest leak, get in touch with a heating engineer straight away. The leaking water could result in corrosion, rust, or cause electrical parts to malfunction.

If you have reached this article, the likelihood is your boiler is already leaking, and while you shouldn’t try to fix the issue yourself, there are a few steps you can take to prevent more water leaking into your home.

  • Turn off the water supply
  • Switch off the heating
  • Clean up any water
  • Contact a qualified engineer

Why is your boiler leaking water?

There are multiple reasons why your boiler might be leaking water and the main cause can normally be identified by where exactly the water is coming from.


Corroded pipes or tanks can eventually start to weaken, which might result in water escaping over time. If the corrosion has not spread further than just one pipe or valve then simply replacing the part that is corroded will solve the problem. In situations where the corrosion has spread further through the system, it is probably beyond repair and means you will have to replace the boiler.


If your boiler pressure is too high then this could lead to your boiler leaking water as the boiler needs to release some of the excess pressure to stop the unit imploding. You will be able to tell if your boiler pressure is too high if the needle on the pressure gauge is pointing anywhere above two. So, if you can see that your boiler pressure is too high you can lower it. The right boiler pressure is between one and two on the pressure gauge.

How to fix pressure issues

Lowering the pressure of your boiler can be done by yourself by ‘bleeding’ the system. Before this however, especially if you have recently topped up your boiler pressure, you should check that the filling loop tap underneath your boiler is securely closed. Make sure the taps are securely closed by pushing them all the way to the left. If you are unsure quickly and only slightly pull the other way to briefly see the increase in pressure before pushing it back to the firmly closed position.

Your next step should be bleeding the radiators which will need some basic tools and is a bit more of a pain. You will need to use a bleed key and loosen the nut on the end of the radiator. As you turn it, water from your system will come out.


Boilers are installed with a temperature control valve (TCV) which monitors the temperature of the water within the boiler and prevents it from getting too high. A leak from the temperature valve could imply that the boiler temperature is too high and burning hot water may start coming out of the taps.

Pump seals

A boiler pump is there to push water around your home’s heating system, so if it isn’t sealed correctly, water can start to leak out. In this case the pump will either need to be replaced or resealed.

Loose joints

Part of the natural wear and tear in a boiler includes pipe and joints connections loosening over time due to the water repeatedly expanding on heating and contracting on cooling. This means that the joints have to be tightened to stop water from coming out.

Poor installation

A leaking boiler could easily be the outcome of poor installation, this is normally the case when water is coming from the pipe fittings. To stop this happening, you should only allow a professional and experienced Gas Safe registered engineer to install a new boiler. You may not necessarily have had a cowboy installation done, small water leaks can be common in new boiler installations and can be tricky for installers to spot. Any conscientious boiler fitter would return to check and correct the work for you to stop any leaks from occurring.

How can you fix a leak underneath your boiler?

If you are sure the pipework underneath your boiler is leaking, you will need a gas engineer to repair it. Even though you shouldn’t try to fix the leak yourself, you can make sure it is contained by placing a bowl or bucket below the boiler or possibly carefully wrapping the leaking pipes in some cloth.

Wear and tear

Like with any appliance, boilers don’t last forever and can wear out over time. If your boiler is over ten years old, it is probably time to think about installing a new one. This will not only be considerably less likely to leak but also boosts the energy efficiency of your home, helping you save money on your bills.

Leaking or faulty heat exchanger

The heat exchanger is the most expensive part of your boiler, and it is not uncommon for them to crack or fail in old boilers and especially cheap lower quality boilers, no matter their age.

How to fix a leaking heat exchanger

Heat exchangers can be replaced by boiler engineers, but it would likely be at a cost that is thought to be false economy. Your best option in this case is to get a new boiler.

Is your boiler leaking an emergency?

A leaking boiler is a serious problem that can not only cause more damage to the boiler itself but also your home. Opting to ignore a leak could result in rust, corrosion, and even mould. At the earliest sign of a leak (even if it looks fairly small) get in touch with a heating engineer, don’t try to fix it yourself.

Can you use your boiler if it is leaking?

If you see a leak or find that your boiler pressure has dropped significantly in a short space of time (implying a leak) then don’t use your boiler. Instead, you should switch off the water supply and central heating and contact a Gas Safe registered engineer.

Does a leaking boiler cause low pressure?

A leak anywhere surrounding your central heating system will result in low boiler pressure. A boiler that has low pressure won’t be able to function efficiently, so getting the leak resolved by an experienced engineer is important.

How dangerous is a boiler leak?

A leaking boiler has the potential to cause a lot of damage, not only to the boiler but to your house as well. It is highly likely that the water will be leaking onto electrical elements that could end up short circuiting. Based on the location of your boiler and how far from it the water has reached, it could possibly lead to damage to furniture, flooring, and other belongings. At this stage you might want to think about a replacement boiler.

How to prevent a boiler leak

The best way to stop your boiler leaking water is with an annual boiler service. This will make sure your system is running smoothly and safely and highlight any possible problems for the trained professional before they can happen. It will also help to maintain your boiler to maximise its lifespan and keep it running reliably.

As well as this, you could have your heating system treated with a chemical flush. A complete flush of the system will get rid of limescale and debris that could help to lower the risk of corrosion. If you are looking for a more long-term solution you could get a magnetic filter fitted which will remove the debris from the heating system before it has a chance to build up.

Why might your boiler stop leaking?

The most likely reason your boiler would stop leaking is that you have switched off your central heating, meaning that the pressure inside the system drops and the leaking stops. Another potential reason could be if your area has experienced heavy rainfall as the water can access the boiler through a badly fitted flue. If this is the case, you should speak to an engineer who will be able to install the flue properly.

How to fix a boiler leak

As previously mentioned you should leave leaking boiler repairs to the professionals, particularly if you suspect the issue is with the internal component. However, in some situations a confident DIY fix could work, for example if you see the water leaking from the pipe joint, dry it off with a cloth and try to tighten it. Sometimes a leak can be due to a loose joint, if you think this might be the case you could try to tighten it.

Should you use a boiler leak sealant?

If the leak is a pinhole, then you might be able to seal it up by using a special additive you add to your central heating system to automatically seal the holes as it circulates through the system. However, these are not always easy to add to your system and in most cases it will not provide a suitable solution.

As you can see there are multiple reasons why your boiler might be leaking water, but whether the leak seems big or small it is always advisable to contact a professional engineer to have your boiler repaired or replaced effectively.

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