Eco Happy (Solar Expert)

Published February 28, 2024

Water and gas leaks from your boiler should always be treated as a priority and with due care.

You must always get professional help if you encounter leaks. However, you can troubleshoot and temporarily patch minor issues until a heating or Gas Safe engineer can inspect the problem.

We have compiled a comprehensive guide on how to locate and repair gas and water leaks in your boiler. We will look at the most common causes of leaks and what you can do to avoid problems in the future. Finally, we will look at the serious dangers associated with leaving leaks unattended.

How To Repair A Boiler Leak – Step By Step Guide

To repair boiler leaks, you first need to identify what type of leak you have. Depending on the type of leak you have, some of the steps below won’t apply. You can pinpoint and address the issue by following this methodical approach.

1. Locate the source of the leak

For a suspected water leak:

  • Start by looking for damp spots, puddles, or mould near your boiler unit. A smell of dampness or mould is also an indicator of a water leak.
  • Check for dampness and drips along the exterior pipework, paying close attention to valves, seals and connections where pipework enters and exits the boiler.
  • If you have a system boiler, repeat this process for the hot water storage tank. If you have a conventional boiler, you also need to check the cold water feed tank.
  • Water dripping from below your boiler indicates an internal problem. You must contact a Gas Safe engineer to perform these repairs safely.

For a suspected gas leak:

  • If you do not have a carbon monoxide detector, perform a smell test. Natural gas is odourless but a chemical called Mercaptan is added to give it a distinct and detectable odour of rotten eggs.
  • Look for black soot forming around your boiler or burn marks.
  • Listen for any whistles or hissing sounds around the boiler which could indicate a gas leak.

2. Shut off the water supply

Before repairing a water leak, you must first shut off the mains water supply using your home’s main stopcock.

Common locations where you will find the main stopcock include:

  • Near the boiler
  • Under the kitchen sink
  • Outside the property, against the house or near the border of the property
  • Near the water meter

The stopcock is usually marked or has a large lever or handle. Turn it in a clockwise direction to close it. If you are struggling to turn the valve, try spraying some lubricating oil on and turning the handle in both directions to loosen it. If that doesn’t work, you can use a wrench or a pair of pliers for extra leverage.

Test the taps in your home after you have shut the stopcock to ensure the water supply is fully turned off.

3. Shut off the gas supply

If you have determined that your boiler is experiencing a gas leak, you must locate the gas shut-off valve near your gas meter box. The gas meter box is usually found in a utility cupboard or inside a wall-mounted box inside your home, although it might be outside your property on an exterior wall or near the border of your property.

Once found, look for the Emergency Control Valve. This may look like a lever or a wheel marked ‘open/close’ or ‘on/off’. Turn the wheel clockwise until the valve is shut, or move the lever 90 degrees to the left or right.

Once the gas is switched off, contact the National Gas Emergency Helpline immediately on 0800 111 999. Ventilate your property and do not turn the gas back on or return inside until a Gas Safe engineer is on site to assist you further.

4. Shut off your central heating system

Before attempting any repairs, you must find your central heating controls and switch them off as a safety precaution. The pipework for the heating system can cause burns and make repairs more difficult if not allowed to cool down.

Generally, you will find the control panel on or near your boiler. Give the system at least 30 minutes to cool down.

5. Drain the water storage tank

If you locate a leak in your water storage tank, you must drain it before you can fix it. Not all boilers have a water storage cylinder; for example, combination boilers heat water directly from the mains.

Make sure that your boiler is switched off and that your mains stopcock is shut. You will need a hosepipe that can run from your boiler to either an outside drain, the bath, the WC, or a sink. It will also help to place a bucket underneath the valve to catch any excess water.

Attach the hose to the drain cock at the bottom of the storage tank. You will see a lever or tap next to the drain cock where you can open the valve to release the water.

Alternatively, if the storage tank is your hot water storage, drain it by opening your hot water taps until the tank has run empty. Always check your boiler manual to make sure you follow the correct process for your boiler model and brand.

6. Tighten loose connections

Nuts and bolts that connect the pipes of your boiler unit to your faucets and heating system need to be tightened securely. If you find a leak coming from a loose connection, use a wrench to tighten it.

 Avoid over-tightening the connection – it might cause further damage to the system.

7. Patch the leak

If the source of a water leak is due to damage to a water storage tank or compromised pipework, you can patch the leak. Do not attempt to patch a gas leak yourself.

Start by using a dry kitchen towel and running it along the storage cylinder and pipes to pinpoint the leak. It can be tricky to spot a small leak on a metal pipe, especially if there is low visibility in the boiler’s location.

You can make patch repairs with special epoxy or putty to seal small holes or damage. Before you place the sealing product, rough up the area around the leak with sandpaper so that the surface is easier for the epoxy or putty seal to adhere to.

Follow the manufacturer’s instructions for the product you choose and allow time for the epoxy or putty to set.

8. Contact a professional engineer

Once you have completed the repairs, or if you’re unable to find and resolve the leak, it’s time to contact registered professionals, like Eco Happy. Even if you feel you have addressed the cause of the leak, getting a certified specialist to double-check the repairs is a good idea.

It takes the right know-how and the right tools to repair a leaking boiler safely, especially in the case of a gas leak.

Our team will assist you with:

  • Replacing deteriorated or damaged seals and gaskets that require exact installation to fix leaks and prevent future leaks.
  • Sourcing and replacing the correct parts for your boiler make and model to resolve leaks.
  • Locating and repairing pipework issues not visible through casual inspection.

Main Causes Of Boiler Leaks

The main causes of boiler leaks are:

Loose pipework connections

Connections in your pipe fittings naturally loosen over time. Factors that cause this include:

  • Thermal expansion and contraction due to temperature fluctuations
  • Vibrations as water moves through during use
  • Improper installation

Boiler pressure issues

If your boiler pressure is too high, it will cause air-tight seals and joins to fail, resulting in a water leak. It also causes your boiler’s pressure release valve to activate as a safety precaution, which will result in your boiler leaking water.

Low pressure is an indicator that there is already a leak somewhere in the system, preventing the unit from reaching optimal operating pressures. Optimal boiler pressure can vary between 1 and 2 bar on the pressure gauge, depending on the unit model and if the boiler is cold or operating

Corrosion and wear

Over time, any boiler will be susceptible to corrosion and wear. The chemicals, minerals, and oxygen present in water can weaken metal surfaces. Once metal surfaces become compromised, it will lead to holes and cracks, resulting in a leaking boiler.

Faulty heat exchanger

The heat exchanger is a device that transfers the heat generated by the boiler to the water needed for your home.

The pipes in heat exchangers are susceptible to the same corrosion and wear that affects the rest of the boiler system.

Some of the more common signs of a faulty heat exchanger include:

  • Strange noises coming from the boiler during operation, including rattling and banging
  • Soot build-up along the outside of the boiler
  • Poor boiler performance

Internal seal leaks

The seals and gaskets within your boiler are under a lot of pressure, literally. They ensure your boiler remains air and water-tight. Over time, they will experience a lot of natural wear and tear, leading to degradation, and ultimately water and gas leaks from your boiler.

Poor installation or maintenance

Shoddy installation or lackadaisical workmanship can even lead to a new boiler leaking water, even if it’s in perfect condition when you purchase it.

While you can fix a leaking boiler, your out-of-pocket expenses will increase. It is best to only have reputable Gas Safe registered engineers work on your boiler system.

 How To Prevent Boiler Leakage

The best way to stop a boiler leaking water or gas is by getting it serviced regularly. Detecting small leaks or corroded pipes, for example, is preferable to having to install a replacement boiler when yours is beyond repair.

Ensuring proper water quality within your boiler is also essential. The water’s mineral content, PH balance, and various sources of chemical and galvanic corrosion can cause leaks over time by reducing the integrity of your pipework.

With these elements in mind, let’s look at the preventative actions you can take in more detail.

Service your boiler annually

Depending on the size, make, and model of your boiler unit, a service can cost as little as £90. Considering that modern boilers can cost £3,000+, it is a no-brainer to have your boiler serviced annually. A service can be even cheaper when included with an annual boiler cover plan which many companies provide.

An annual service will ensure that leaks and potential leaks are identified early. Some boiler warranties also require you to perform a service to get full coverage.

Perform a chemical flush

Chemical flushes are a great way to ensure the prolonged lifespan of your boiler and can also improve performance. This procedure is quite tricky and ideally needs to be carried out by a Gas Safe engineer.

They will flush the system using special chemicals. This flush will loosen and dissolve a variety of contaminants. Contaminants will cause corrosion and blockages in pipes that will lead to leaks.

Install a magnetic boiler filter

A magnetic boiler filter is a common device that can be installed by a heating engineer. It contains powerful magnets as well as a basic water filter device. It removes both ferrous and non-ferrous materials from your water. These materials include iron oxides, rust particles and other metallic debris.

These particles will accumulate within any boiler with regular use. By removing them, it will prevent future leaks caused by compromised pipework.

Is A Leaking Boiler Dangerous?

Yes. When a boiler is leaking, especially gas, it can pose a serious risk to your health and property.

Below are the dangers leaks can pose if not addressed.

  • Fire hazard – Traditional boilers rely on the combustion of fuels such as natural gas, oil, or propane to heat water which can pose a fire risk if they leak out. Additionally, electrical components could be near leaking water which could cause a short and result in a fire.
  • Carbon monoxide – This dangerous gas is, under normal circumstances, vented outside the home. A boiler leaking gas can put your health at serious risk.
  • Mildew and mould – Leaks lead to damp spots which can cause fungus to spread in your home. This can pose a severe health risk for your respiratory system, as well as cause property damage.
  • Water damage – Untreated leaks can penetrate porous materials. This leads to damage to the wood and paintwork of ceilings, walls and floors. It can also delaminate plywood and rust metal fixtures.

Do I Need To Replace My Leaking Boiler?

You generally do not need to replace your whole boiler if you have a leak. A qualified heating or Gas Safe engineer can perform the necessary repairs to restore your boiler to full, safe functionality.

While basic water leaks can be resolved with DIY repairs, it is still important to have a professional inspect your boiler afterwards to ensure that your unit is deemed operationally safe.

Let’s look at some scenarios where it would be better to replace a leaking boiler, rather than repair it:

  • Boilers 10+ years old should be replaced due to the increased risk of further leaks after initial repairs.
  • If you have a new boiler and you are experiencing regular leaks, it is an indicator of a larger issue with the unit.
  • If you have an old boiler that is out of warranty or using discontinued parts, it will make repairing leaks more expensive and time-consuming than just replacing the whole unit. This has a specific term in the industry called Beyond Economical Repair.


Why is my boiler leaking water when the heating is on?

There are a few reasons why your boiler is leaking when your heating is on. It could indicate a failure of the pressure relief valve. It could also be a faulty water expansion tank, a condensate pipe blockage or any of the common faults we have mentioned in this article. It is best to contact a professional to assess the problem and make the appropriate repairs.

Can I use my boiler if it is leaking?

You should avoid using a leaking boiler until the fault is repaired. You risk further damage to the boiler and damage to your property if you continue to use it in a compromised state. Not to mention the boiler will be running with reduced efficiency, which will increase your energy bills.


To fix a leaking boiler, you need to take careful and focused action. Locating the source of the leak should be your first step. From here you can narrow down the potential root causes. Once you have made the necessary repairs, closely monitor the leaks.

No matter how small the problem is, we always suggest you call in a registered heating or Gas Safe engineer to do a proper assessment.

When it comes time for a boiler replacement, check out our helpful boiler guide to find the best boiler for your home’s needs. Contact Eco Happy and check out our affordable quotes to get the best deals on the ideal heating solution for you and your family.

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