What causes a gas leak?

Gas leaks in the home are usually the result of poorly fitted, badly maintained or faulty appliances like boilers and cookers.

If your appliance is badly fitted, gas can escape — typically from the gas hose that leads into your appliance or from around the seal — so you should always make sure your appliances are installed by an accredited Gas Safe engineer (previously CORGI).

If you are not sure if your engineer is accredited, you can check the Gas Safe site, or ask the engineer to show their registration card.

Likewise, if your appliances are a bit older and you are having them serviced, always use a Gas Safe engineer.

You should also be cautious of old or second-hand appliances, particularly if you are just moving into a new property or renting. Luckily there are some easy-to-spot signs that will tell you if your old appliances are faulty (which we cover below).

What can happen if a gas leak isn't dealt with?

A gas leak can lead to carbon monoxide poisoning, fires and even explosions.

The infographic below was compiled by the Gas Safe Register (GSR) using its data around gas callouts. It highlights that in the past three years, one in six homes inspected by the organisation had an unsafe gas appliance. If left unchecked, these appliances could have led to fires, explosions and poisonings.

It also highlights, again using GSR data, which cities are the most dangerous and the safest when it comes to gas safety. Birmingham was named the most dangerous with 34% of its appliances found to be unsafe; Brighton was the safest, with only 5.4% of its appliances found to be a gas danger.

Right click on the image and select "open in a new tab" to see a larger version.

So, if you smell gas, you should take immediate action.

How do you detect a gas leak?

The most tell-tale sign of a leak is the smell of gas in your home. But there are also particular physical symptoms you may suffer from if there is a leak.

If you are feeling lightheaded, ill, dizzy or nauseous you should go outside immediately. If the symptoms go away in the fresh air you could be feeling the effects of a gas leak or carbon monoxide poisoning.

There can also be some clear signs from your household appliances that can indicate a leak, even if you can't smell gas:

  • Always look for a crisp blue flame, rather than an orange or yellow flame.
  • Likewise, look out for a pilot light that always seems to blow out.
  • On the outside of the appliance watch out for soot or any black or brown scorched areas around your appliances.
  • Watch out for excessive condensation on the windows, or a musty smell in the air.

What should I do if I smell gas?

To avoid the worst, you should always take action immediately if you smell gas in your home.


The first step is to turn off the gas supply at your gas meter. The valve that regulates the flow of gas will be connected to your pipe at a right angle, but can sometimes be difficult to locate and/or hard to access.

That's why you should always familiarise yourself with whether your gas supply can be turned off — especially if you're in a new property or have recently made changes to the layout.

The next step is to get fresh air into your home to help disperse the gas. Open all the windows and doors and leave them open to ensure air flow.

If you can't open the windows because they're locked or for any other reason, get outside and into the fresh air as soon as possible.

While you are airing out your home, avoid using any electrical switches, as the sparks could cause an explosion. This includes light switches or electronic doorbells. Similarly, avoid smoking, using matches or burning any naked flames (e.g. candles) as they could all ignite the leaked gas.

Once you have taken these steps and dealt with the imminent danger, it is time to call in the experts. The National Gas emergency number is 0800 111 999, but don't just rely on memory. Save the number in your phone book and have it written down in an easily accessible location, like on a noticeboard in the kitchen.

The number is free to call and is available 24 hours a day. Crucially, do not call on a mobile phone inside your home if you suspect a gas leak, rather go outside or to a neighbour’s home if you have to use your mobile. Remember, no electrical device use if you suspect a leak.

Once you have called the number, make sure someone is around to help the emergency engineer locate the leak and gain access to the property once they arrive.

Finally, in the unlikely event that a fire breaks out, your first call should be to the fire service on 999.

Most mobile handsets will allow you to dial the emergency number even if there is no SIM inserted, or even if the phone has no credit.

How do I prevent gas leaks?

It is far easier to deal with a gas leak by stopping it from occurring in the first place. Your first line of defence is with your household appliances.

Always make sure they are installed by an accredited Gas Safe Register engineer, and make sure you check them on a regular basis for signs of wear and tear.

Likewise, if they do require maintenance, make sure your engineer is registered. You should also keep an audible carbon monoxide alarm in your home. These are cheap to purchase from DIY stores and look just like smoke alarms. Make sure they are installed in an open space like a hallway, and change the batteries annually.


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