Smell gas in your house? What to do now, and after it is made safe

The first five minutes

Gas in a home is given a strong added smell precisely so that you notice it before it builds up. Natural gas has almost no smell of its own. The sulphur or rotten-egg smell is the warning, and it is worth treating every occurrence as real until someone with the right equipment says otherwise.

Work through these steps in order. None of them needs tools, and none of them involves looking for the leak yourself.

• Put out cigarettes, candles and any open flame. Do not strike a match or use a lighter to look around.
• Do not operate electrical switches, including light switches, doorbells and plug sockets, on or off. A switch can spark.
• Open doors and windows to let the gas disperse.
• Turn the gas off at the emergency control valve next to the meter if it is safe to reach. The handle is on when it lines up with the pipe and off when it is turned a quarter turn across it.
• Get everyone out of the building, including pets.
• Call the National Gas Emergency Service on 0800 111 999 from outside, and wait for them away from the building.

If anyone feels unwell with headaches, dizziness, nausea, breathlessness or confusion, get them into fresh air and seek medical help straight away. Those are also the signs of carbon monoxide poisoning, which has no smell at all.

Where the smell usually comes from

Once the emergency engineer has been, it helps to understand what they are likely to have found. In a typical London house or flat, a gas smell tends to come from one of a small number of places.

A hob or oven tap left partly on without lighting is the most common innocent cause. Next is the flexible hose and bayonet connection behind a freestanding cooker, which gets pushed and pulled every time the cooker is moved to clean behind it. After that come leaking joints on older pipework, often under floors or in cupboards where the pipe has been disturbed by other work, and faults on the boiler, gas fire or meter itself.

A smell that appears only when the boiler or a fire starts up, or only after someone has been working on the kitchen or floorboards, is useful information. Tell whoever attends exactly when you noticed it and what had changed.

Is it gas or the drains?

Sewer gas can also smell of rotten eggs, and people sometimes mistake one for the other. A drain smell is usually strongest near a sink, shower, toilet or floor drain, often gets worse when a trap has dried out, and tends to come and go with water use or the weather. A gas smell is more often near the cooker, the meter, the boiler or along the route of the gas pipe.

Do not try to decide which it is by sniffing around the house. If there is any chance it is gas, treat it as gas and call the emergency number. If the emergency engineer finds no gas escape, our guide to telling water smells from drain smells and the one on sewage smells inside the home will help you track down the real cause.

What the emergency engineer does, and does not do

The National Gas Emergency Service is there to make the situation safe, not to repair your installation. The engineer will look for the escape, and if it is inside your property they will usually turn off the supply to the faulty appliance or isolate the whole meter.

If an appliance or part of the pipework is found to be unsafe, they may fix a warning label to it and disconnect it. Do not reconnect it, turn the valve back on or use the appliance while that label is in place. Their job ends once the property is safe. Finding and fixing the leak on your side of the meter is your responsibility, or your landlord's if you rent, and it has to be done by a Gas Safe registered engineer.

Getting the gas back on safely

When our engineer arrives after the gas has been made safe, the work usually follows the same pattern. They will check what the emergency engineer isolated and why, then carry out a tightness test on the installation to confirm whether it is holding gas. If it is not, they trace the leak along the pipe run and at each appliance connection, repair or replace the faulty joint, section of pipe, hose or appliance valve, and test again.

Only when the installation passes, and any appliance that was condemned has been repaired or safely disconnected, is the supply turned back on. Appliances are then relit and checked to make sure they are burning properly. You should be told clearly what was found, what was repaired and whether anything remains out of use.

If the source was an old cooker hose, the boiler or a gas fire, the engineer may recommend a replacement rather than a repair. That is a conversation to have once the installation is proven safe, not before. If you are not sure where your meter or its lever is, our guide on how to turn off the gas at the meter shows where to look in houses and flats and which way is off.

Tenants and landlords

If you rent, call 0800 111 999 first and your landlord or letting agent straight afterwards. The landlord is responsible for the gas pipework and any appliances they supplied, and must keep them safe with an annual gas safety check. Keep a note of the time you called, the emergency engineer's findings and any warning label left on an appliance, and pass it on.

Landlords and agents managing properties across London can book the follow-up repair and a new gas safety record through our gas safety certificates service once the leak has been fixed.

Afterwards: reducing the chance of it happening again

Most gas escapes in homes come from parts that are disturbed or aged. A few habits make a real difference: do not drag a freestanding cooker out without checking the hose has slack, have gas appliances serviced as the manufacturer recommends, and make sure anyone working near gas pipes knows where they run. Fit an audible carbon monoxide alarm in rooms with a gas appliance, and test it. Our guides to carbon monoxide signs at home and a carbon monoxide alarm beeping explain what those alarms are telling you.

Loyal Plumbers works 24 hours a day across London and everywhere inside the M25, with 10 vans on the road. All gas work is carried out by Gas Safe registered engineers. Once the emergency service has made the property safe, call 020 4652 8585 and tell us what they isolated, whether a warning label was left and which appliances you need back in use. Our call-out charge is £60, and the engineer explains what they have found and what the repair involves before starting any work.