Is water leaking from your boiler? Here's what to do

Finding water leaking from your boiler can be worrying; your mind instantly rushes to thoughts of how much it costs to call a qualified engineer to inspect and solve the issue. If you have an old appliance, you might think it's time for a new boiler, which means spending thousands on modern boilers.

In reality, fixing the problem may be relatively straightforward and inexpensive.

To give you peace of mind and help you work out what the problem with your boiler is, we put together this guide. Here, we explore what to do if your boiler is leaking water, what might have caused the leak, and how a Gas Safe registered engineer could solve the problem.

What to do if your boiler is leaking water

The cause of your leaking boiler could be any number of issues, like high water pressure, worn seals or o-rings. If you have an older boiler, it could be caused by a damaged water manifold or even corroded pipes.
If you recently had a new boiler installed, the system may be leaking water due to increased pressure on older joints.

As soon as you notice a leak, you need to do something about it. A boiler leaking water can damage pipes, cause rust, or even get into electrical components.

When you find a leak, you must do the following:

• Turn off your heating
• Turn off the water supply to the boiler
• Contain the water leakage if possible using a bucket or tub, for example
• Contact a Gas Safe registered engineer

You must call a Gas Safe registered engineer to inspect and fix your leaking boiler. You should never try to fix a boiler leak yourself, as this may cause further issues and endanger you and the people you live with.

Why is your boiler leaking water?

There is more than one reason why your boiler could be leaking water, and the location of the leak can indicate the specific issue.

Before you call someone to fix the problem, you must determine where the leak originated. Some of the leading causes of a leaky boiler include:

1. High boiler pressure

Over pressurising your boiler, or accidentally leaving the filling loop open can cause high boiler pressure. A split or passing heat exchanger can also cause the same symptom on a combi boiler for example.

If the boiler's pressure is too high, the pressure relief valve may try to release some water out of the heating system to reduce it (typically if the pressure exceeds 3 bar or is in the red zone on the gauge). You might need to bleed your radiators to help further reduce the pressure by manually removing excess water from your system. 

Read our full guide on how to bleed your radiators for step-by-step instructions.

2. Corrosion in your heating system

Mainly a problem in older boilers; corrosion can cause pipes in your heating systems to block as they fill with rust or other debris. Corrosion can weaken pipes, the rubber seals or washers that protect the joint between two connecting pipes.

If there is widespread corrosion, you may have to replace the central heating system, including a boiler replacement.

3. A faulty heat exchanger

The job of the heat exchanger is to transfer the heat generated by the burnt gas to the water inside it, and that hot water then circulates around the central heating pipework, so it's crucial that it works properly. If your heat exchanger starts to leak water, it's a problem that needs professional attention and would need replacing.

You won't be able to spot a faulty heat exchanger, as finding the component involves taking the cover off the boiler, but a Gas Safe registered engineer should be able to check for signs of leaks during your annual boiler service and advise you on any potential issues.
For more information on how your boiler works, check out our helpful guides!

Boiler leaks by location

The location of the boiler’s leak can give away some information as to what the problem is, as we explore below: 

1. Boiler dripping water from underneath

If you notice water leaking from the boiler pipework, this could be because of loose water fittings and joints, cracked or corroded water manifolds or pipework within the boiler. Water leaks are unfortunately common in boiler installations, so don't panic; call the Gas Safe registered engineer who fitted or services the boiler, and they can come and inspect and hopefully fix the leaks and pipework.

2. Leaking heat exchanger

Due to the location of the heat exchanger or heat exchangers, you'll have to get a Gas Safe registered engineer to investigate whether you have a leak on these components. The signs of a leaking heat exchanger include:

• The boiler is leaking from the bottom - if you notice a leak but can't find where it's coming from, it may be the heat exchanger. Call a Gas Safe registered engineer to take a closer look.
• Your carbon monoxide detector is going off - a cracked heat exchanger in certain boiler types may leak carbon monoxide. If this happens, turn your boiler off and don't turn it back on until an engineer has checked over the system.

3. Leaks along seals of internal parts

Over time, boiler seals, washers and pipe fittings can decay, which may lead to the heating system or boiler leaking water.

To check for leaks on seals, a Gas Safe Registered heating engineer will remove the boiler cover and inspect the relevant components. 

You should not attempt to fix leaking boiler seals on your own, as this could cause more problems. A Gas Safe registered engineer should inspect and repair the leaks where possible.

What should you do if you find your boiler leaking water?

Upon finding your boiler leaking water, you should turn off the electric supply to the appliance. This will mitigate the risk of electric shock and reduce the risk of further damaging your boiler.

Locate your home’s water stop tap and turn this off, then see if the leak slows or stops. Or alternatively, if you can isolate the boiler's water supply

Try to contain the leak with containers or towels temporarily to try and reduce further damage.

Once you've done this, it's time to check your boiler's pressure gauge. If the pressure is high, this may be the reason why water is leaking from the boiler. To reduce the pressure, you could try to bleed the radiators to release some air and water from your heating system. Equally, low pressure can also be a sign that you have a leak in your heating system.

After checking the pressure and bleeding radiators, you will need to ring a Gas Safe Registered engineer to investigate the problem further; even if you're confident that bleeding the radiators has solved the issue, we recommend getting an expert's opinion.

How to prevent boiler leaks in the future

A boiler leak can be a real pain, leaving you without heating or hot water, not to mention the potentially expensive cost of solving the problem.

The most effective way to prevent your boiler from leaking water is to keep it well-maintained and have it serviced regularly. This way, a Gas Safe registered heating engineer can spot and fix any signs of corroded pipes before you notice a water leak - potentially saving you hundreds of pounds on parts and repairs. Also, you could keep an eye on the pressure gauge if this is low; it could be pointing to a leak you aren't aware of.

If you’re unsure how best to maintain and look after your boiler, here are 5 ways BOXT offers unbeatable aftercare. 

Is a leaking boiler dangerous?

A leaking boiler isn't necessarily dangerous or expensive to fix; however, upon finding a leak, you should contact a professional engineer as soon as possible.

Remember, a boiler leak doesn't necessarily have to be water - gas leaks can occur too. Call the National Gas Emergency Services immediately on 0800 111 999 if you smell gas anywhere in or around your home.

Take the stress out of boiler maintenance with BOXT

With a Home Cover Plan from BOXT, you can pay for your annual boiler service and year-round boiler cover on a rolling monthly basis for budget-friendly peace of mind.

Better still, if you buy a new appliance from us, we'll include a magnetic boiler filter as part of the boiler installation process. Having a magnetic filter fitted means metallic particles have less chance of finding their way into your heating system and disrupting the water flow. Discover more about magnetic filters over on the blog.

For more information on maintaining your boiler and avoiding expensive boiler repairs, check out the BOXT blog. Here, you'll find advice on everything you need to know about boiler maintenance, from how long a boiler lasts to how to clean a magnetic filter.