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Why is my boiler leaking water?

It doesn’t matter whether your boiler is leaking gas or water, a boiler leak should not be treated lightly. Whilst most faults are repairable, for safety and legal reasons you should not attempt to repair a boiler unless you are sufficiently qualified.

It doesn’t matter whether your boiler is leaking gas or water, a boiler leak should not be treated lightly. Modern heating systems are sealed and pressurised so water has no room to escape. A leak signifies an internal issue, meaning there are many elements that could be at fault. Whilst most faults are repairable, for safety and legal reasons you should not attempt to repair a boiler unless you are sufficiently qualified.

A boiler typically lasts around 20 years, so if your boiler is around this age it may need replacing. A boiler specialist will be able to assess whether your system needs to be replaced or can be fixed.

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Why is my boiler leaking water?

A leaking boiler could signal quite a number of issues. The following are the most common:

Boiler is leaking water from the bottom

If your boiler is dripping from the bottom, small leaks could point to a pressure issue within your system. All boilers are fitted with an outlet pipe that releases extra pressure. For the pressure to escape, the outlet pipe is not sealed like the rest of the system, therefore it can release some extra water.

engineer fixing boiler pipes

A small amount of water is nothing to worry about, a large leak could mean there is too much water pressure inside the system. If you are seeing large leaks, check your boiler’s pressure gauge. Note if the needle is pointing to green or red, if it is red, you will need to bleed your boiler.  You can get rid of excess water yourself using the release valve, most boilers will have one.

Heat exchanger

The heat exchanger is where your boiler warms up cold water. When hot gas flows through the pipes, they expand. As the water begins to cool down, the metal pipes will contract. Frequent temperature changes and general use can cause the metal to become weak and eventually crack.

Heat exchangers are the most expensive component within a boiler, they tend to be the first component to malfunction in cheaper low-cost systems. A damaged heat exchanger will most likely mean you need a new boiler.

Sealant issues

With a new boiler, the joints where the pipes lead to the boiler could be damaged or incorrectly sealed. Seals inside your boiler can also decay over time, especially if your boiler is over pressured. You can check for leaks in your seals if you feel comfortable removing your boiler cover. The pipes will be extremely hot so do not touch anything under the boiler cover.

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How to fix a leaking boiler

There are a few immediate steps you can take in the aftermath of a boiler leak.

  • Turn off your water supply to keep the puddle from growing, you can do this by turning off the internal stop tap.
  • Drain the system. Your boiler will have leftover water inside, to drain your boiler run the tap or flush the toilet after your water has been turned off. This will get rid of leftover water in the system.
  • Once you’ve looked after the immediate leak, check your insurance policy to see if you are covered, if the damage is extensive. Most cover will be provided in the case of broken or burst pipes.

How to stop a leaking boiler

It’s worth repeating; always leave leaking boiler repair to a professional. Boilers are not just full of hot water, they are gas appliances. If you are an amateur trying to fix a boiler, there is a risk of a dangerous, potential gas leak. A botched DIY job could also leave you paying more money than the cost of hiring a heating engineer.

To better understand the issue with your boiler, try resetting it to see if that helps. If your boiler is not fixed after two resets you will need to contact a specialist. You can also check your pipework for corrosion or rust, this will indicate if your boiler is past its best.  A boiler specialist will be able to fix your problem or install a new boiler for you.

It’s worth getting a boiler service every year to ensure everything is running smoothly, find out more about the cost of boiler servicing.

Leaking boiler repair

Boiler repairs and replacements are a necessary cost when owning property. A high-quality boiler fitted correctly will be expensive at first, but will last for a long time. Boilers do vary in cost depending on the features you would like, most standard boilers will cost between £3,000 – £4000. Hiring a heating engineer to fit your new boiler or repair a leak, will cost around £40 £50 an hour depending on the area you live in.


Why is my boiler leaking from underneath?

Corroded or ill-fitting pipes will leak. Take off the boiler cover to examine your pipes, but do not touch them as they will be very hot. Take a look at some common boiler faults in more detail.

How much does a new boiler cost?

A new heat-only boiler will cost on average £3,075. Find out more about new boiler costs in our cost guide. For a full boiler repair guide, visit our boiler repair cost guide.

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