A boiler that is leaking water isn’t a good thing and, if left, can lead to further problems. Usually, it’s just a sign that a seal or a valve has developed a fault, however when left, it can cause other components to rust and can even damage the electrical components within the boiler. Your best option when you notice a leak is to fix the problem quickly and prevent any future damage.

Below, you can find out how to determine a probable cause. Remember that if you’re not confident at fixing it yourself or you need to take the cover off to get inside the boiler, you should call a registered Gas Safe engineer to take a look and fix the issue for you.

Why is my boiler leaking?

Before you can do anything with your boiler, you need to find out why it’s leaking, but this isn’t always easy. The first thing to do is find where the water is coming from, as this will give you a better idea. Below, we’ve listed some of the main causes

High boiler pressure

Have you ever noticed the pressure gauge on the front of your boiler? This is important as it tells you how much pressure there is in the system. Too little or too much pressure can cause a problem and so you should check the valve every now and then and add or remove water as required.

If your boiler is leaking, you should check the pressure gauge to see if the pressure is too high. If this is the case, it’s likely that the pressure relief valve (PRV) is trying to release some of the water in the system to bring the pressure back down to a comfortable level. The valve needle should be between one and 1.5 bar (usually shown on the gauge as a green zone). If the needle is higher than this, or in the red zone, you may need to bleed the radiators to release extra water. 

Corrosion in your system

Corrosion can be a problem in older boiler systems as it can cause rust and other debris to build up within your radiators and pipework. As the water runs around the system, it can pick up this debris and return it to your boiler as well. The older the system, the more likely you are to have issues with corrosion. The only problem is, many people don’t know it’s there as it can’t be seen.

Corrosion can also break the rubber seals around the joint of two pipes, so water may be leaking through here. If the corrosion is on an individual component, a Gas Safe engineer will be able to replace this with ease. However, if the corrosion is widespread, then you may need to replace the boiler and central heating system completely. An engineer will be able to advise if a new system is required or if a new boiler and flushing the system would be adequate. If you have an old boiler, replacing it with a newer model could make your home more efficient and you could save money on your gas bills too.

Faulty heat exchanger

The heat exchanger is the part that allows your boiler to heat cold water, so it’s a very important part of the appliance. Unfortunately, a leak can be a sign that the heat exchanger is starting to decay. It’s not uncommon for this part to crack in some models over time, and it can be expensive to replace. This isn’t a problem that you’ll be able to diagnose yourself, as it involves taking off the cover of the boiler and looking inside. Therefore, you should call a Gas Safe engineer to check the issue for you. Some are more susceptible to corrosion due to the materials they are made from. Viessmann heat exchangers offer a 10 year warranty.

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Is a leaking boiler dangerous?

A boiler that’s leaking water should be checked to ensure that the problem is solved quickly so it doesn’t get any worse. 

How to fix a leaking boiler 

Now that you know why your boiler might be leaking, you need to know how to fix the issue.

As we’ve mentioned, first you should check the pressure gauge and if the pressure is too high, bleed some of your radiators to release a bit of water. This should help with the issue.

Next, you should see if the water is coming from around any visible pipe fittings or joints. To check, dab the area dry then wait to see if the water appears again. If it does, you can try turning the connector by just a quarter turn using a spanner to see if this tightening does the job. However, corrosion can cause seals to wear away, allowing water to escape. If this is the issue, you’ll need to get a suitably qualified heating engineer out to take a look at the seals and replace them where necessary. It may even be that a seal has come loose and just needs to be tightened.

If you cannot determine the issue yourself or need someone else to delve a little bit deeper into the problem, you should call an engineer. There are many excellent engineers who will give impartial advice as to the most cost effective solution to fixing your boiler leaking water.

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