For support call: 0330 100 3142
Find an Installer

Is your boiler leaking water? What to check

Your boiler is an essential part of your home that provides heating and hot water needs for your home.

If you notice your boiler is leaking water, it could be due to a number of different risk factors. As boilers are complex appliances, it’s important to know what you do when you find your boiler leaking water.

A leaky boiler can quickly become a serious concern, we highly recommend you contact your local gas safe engineer to come and have a look at the leak so they can fix any problem and assure you it’s in a safe condition.

In this guide, we'll explain some of the common causes of boiler leaks and what can be done to look after your heating system so that these leaks don’t become a regular problem.

Corrosion in your system

Corrosion happens when any iron in your boiler is exposed to water and oxygen, causing rust to form and the metal to begin breaking down. This can weaken the pipe fittings and storage tanks of the boiler, meaning water can begin to leak out of the weakened section. It’s important to mention that corrosion and rust can also occur in pipes and radiators and not always the boiler components. Check any exposed pipes regularly as it will help with the overall health of your heating system.

If you find your boiler leaking brown water this can indicate sludge, which is a mix of rust and dirt that builds up over time. When the corrosion is only present in one part of the boiler (e.g one pipe, one valve) then you can simply replace that part and that will solve the issue. However, if the corrosion has spread throughout the system, then you may need to replace the whole boiler.

High boiler pressure

A high boiler pressure can cause a large strain on a boiler system, meaning all that extra pressure needs somewhere to go.

To stop the boiler system from failing, the unit may let out some of that extra pressure through pressure relief valve (PRV). Since the outflow pipe doesn’t have sealed fittings some drops of water might leak out even if it’s working normally.

Check your boiler's pressure gauge, if it's above 2 when it's running and the system is warm, then this indicates higher pressure than normal. If you want further advice on your boiler's pressure, call your local installer who can check your boiler to see why there is a problem.

Loose joints

Like the outlet pipe mentioned above, any kind of looseness or gaps in a boiler can cause water to leak out. A boiler must be a tightly sealed unit as the water inside the boiler constantly expands when it’s hot and contracts when it’s cold, the pipe connections and joints can begin to get worn over time.

Damage to seals

If you find that your boiler is leaking then it’s possible that there may be damage to some of the seals, which then allows water to begin leaking out of the system. This can sometimes be due to high boiler pressure but is usually a sign of long-term decay.

If the damage is minor then new seals are a quick way to solve the problem. However, if the decay and corrosion has spread then you may find buying a new unit to be more cost effective. Remember, only a gas safe engineer can check inside the boiler to see what is leaking, don't attempt to fix any leaks yourself.

Boiler pump seals

The boiler pump works by keeping the water flowing through the heating system, meaning if the seals in the pump begin to weaken then water can start leaking out.

If the issue is the pump or seals then it’s generally easiest to simply call a gas safe engineer and replace the faulty component.

Although you can’t prevent the wear and tear of pump seals completely, routinely inspecting your pump can make sure you catch any issues early on, since it’s more cost effective to replace a single seal than the entire pump. Always get your boiler serviced annually by a gas safe registered engineer.

What to check if your boiler is leaking

A leaking boiler can develop into a larger issue if the cause isn’t identified and dealt with quickly. If your boiler begins to leak then you can give it a basic check yourself to try and find a probable cause (anything beyond a surface level check should be by a certified engineer).

Firstly, you should find where the water is leaking from, either from what part is visibly leaking or to see if it’s leaking internally with damp patches below the boiler.

Secondly, check all the gauges of your boiler such as its pressure and temperature to see if either is higher than normal, as high pressure is one of the most common causes of a leaky boiler (anything above 2 is an issue). Finally look over your boiler for obvious signs of corrosion, as that would indicate wear and tear which needs to be replaced.

How to fix a boiler leak

Whether the issue with a leaky boiler is obvious or not it should only ever be repaired by a certified heating engineer. Boilers are intricate systems and using the services of a qualified professional ensures that everything is done according to regulations. If you’ve just identified a leak there are several things you can do:

Contain the leak with a bucket, container or some form of absorbent material, stopping a water puddle from forming and damaging anything around the boiler

If possible, you should isolate the boiler water supply

If you can’t contain the leak, then turn off the mains cold water stop tap and switch off the electrical supply to the boiler


Once you have done all of these then you must call a certified Gas Safe Engineer and have them properly examine your boiler.


Why is my boiler leaking water from underneath?

The boiler is poorly installed

If water is leaking from underneath the boiler then it’s very possible that some of the joints weren’t fitted correctly when the unit was installed.

This is even more likely if it’s a new boiler that’s leaking, as small leaks are relatively common with new installations.

If you do experience issues then contact the boiler installer and have them make adjustments.

Pipes are corroded

If the leak is coming from beneath the boiler then it’s also possible that some of the pipes have corroded.

When pipes corrode and become very brittle they can break, causing leaks. To maintain your boiler, have it serviced annually, as it’s more cost effective r and easier to replace a single corroded pipe than a whole unit.

The more leaks you have may also be an indicator of how corroded your boiler is internally.

Why is my boiler leaking water from the pressure relief pipe?

If you find your combi boiler leaking water then you may want to check the pressure relief pipe. This is usually a copper pipe leading from your combination boiler to the outside of your house, where it can let water flow out if there’s too much water in the system.

If your pressure relief pipe is leaking continuously or for no apparent reason then it may mean there’s an issue with your boiler.

Your overflow pipe may leak water if:

The purpose of a pressure relief pipe is to allow water to be removed from the system if the boiler pressure gets too high. Modern boilers are fitted with expansion vessels, a large tank that can contract and expand to keep the boiler pressure constant as temperatures change.

The boiler’s Pressure Relief Valve (PRV) is a safety device which protects your heating system from high pressure, with a boiler generally wanting a pressure between 1-2 to work safely. The PRV will operate if pressure builds up and water will come out of the pressure relief pipe outside.

This could mean that the PRV may have failed and is leaking or the expansion vessel needs to be replaced.

As boiler systems are quite complex it’s always best to contact a certified gas safe engineer to make any adjustments to your system.

They will be able to replace the component and if there are any steps to help to prevent the overflow pipe from leaking again.

If your boiler is leaking, Glow-worm offers a certified boiler repair service that can solve any issues.

Alternatively, our annual boiler service can ensure any corrosion and general wear doesn’t get an opportunity to spread. Finally if your boiler is due an upgrade, we offer a replacement boiler service where our installers can offer technical advice about what type of boiler is best suited to your home. Upgrading your boiler can help reduce your running costs as modern systems are much more energy efficient. Contact your local Glow-worm installer here.