Do not try to find the leak yourself. Open doors and windows, do not touch any electrical switches, do not light a match or smoke, and leave the property. Then call the National Gas Emergency Service on 0800 111 999 from outside. The line is free and open at all hours.
To detect a gas leak, trust your senses first: natural gas smells of rotten eggs because suppliers add a scent to it. You might also hear hissing near a pipe or appliance. If you suspect a leak, do not investigate it yourself. Leave, avoid switches and flames, and call 0800 111 999. Finding and repairing the leak is a job for a Gas Safe registered engineer.
A gas leak is one of those problems where the safest first move is to do less, not more. The instinct to hunt down the source and have a poke about is natural, but with gas it is exactly the wrong thing to do. This guide explains how to recognise a leak, what to do the moment you suspect one, how professionals detect it safely, and where carbon monoxide fits in. The aim is to keep you and your household safe, then get the right qualified person to the property.
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The signs of a gas leak
Natural gas has no smell of its own. To make leaks noticeable, gas suppliers add a chemical called mercaptan, which gives it that unmistakable rotten-egg or sulphur odour. If you catch that smell indoors, treat it as a leak until proven otherwise. Alongside the smell, there are a few other signs worth knowing.
- A rotten-egg or sulphur smell, the clearest and most common warning.
- A hissing or whistling sound near a gas pipe, meter or appliance.
- A pilot light that keeps blowing out, or a gas hob flame that burns lazy yellow or orange instead of crisp blue.
- Sooty marks or dark staining around a boiler, fire or other gas appliance.
- Higher gas bills with no change in how much you use, which can point to gas escaping somewhere.
Outside, a gas leak from a buried supply pipe can show up as patches of dead or dying grass, or as bubbling in standing water. These outdoor signs still warrant the same call to the emergency line. Trust the smell above everything else: if it is there, act on it.
What to do if you smell gas
The official steps from the National Gas Emergency Service are simple, and the order matters. The priority is to make the area safe and avoid anything that could ignite the gas, not to find where it is coming from.
- Open doors and windows to let the gas clear and fresh air in.
- Do not touch electrical switches. Leave them as they are, whether on or off. A spark from a switch can ignite gas.
- Do not smoke, light a match or use a naked flame of any kind.
- Turn the gas off at the meter using the control handle, unless your meter is in a cellar.
- Leave the property and call the National Gas Emergency Service on 0800 111 999 from outside or from a neighbour's house.
The Health and Safety Executive adds that if you are in any doubt, you should leave the building and tell the police as well as the emergency line. Do not turn the gas supply back on until the leak has been dealt with by a competent person. The emergency engineer who attends will make the situation safe, but they are not there to repair your appliance. That repair comes next, and it has to be done by a registered professional.
Gas leak or carbon monoxide?
People often use "gas leak" to mean two different dangers, and it helps to keep them apart. One is escaping natural gas, which you can smell. The other is carbon monoxide, a poisonous gas produced when fuel burns incompletely in a faulty appliance. According to the NHS, carbon monoxide is colourless and has no smell, so you cannot rely on your senses to detect it the way you can with natural gas.
That is what makes carbon monoxide so dangerous, and why a separate alarm matters. Watch for these clues that an appliance may be producing it:
| Warning sign on the appliance | What you might feel |
|---|---|
| A lazy yellow or orange flame instead of crisp blue | Headaches that ease when you leave the house |
| Dark, sooty staining on or around the appliance | Dizziness, nausea and breathlessness |
| Pilot lights that frequently blow out | Tiredness and confusion, like flu without a temperature |
| More condensation than usual on nearby windows | Symptoms shared by others in the household at the same time |
The NHS notes that mild carbon monoxide symptoms are easy to mistake for a cold, flu or simple tiredness, and that they often improve once you are out in fresh air. If you suspect carbon monoxide from a gas appliance, get everyone out, call 0800 111 999, and seek medical advice. A working, audible carbon monoxide alarm near your sleeping areas is the single best early warning, because the gas itself gives you nothing to notice.
How professionals detect a gas leak
Once the area is safe and the supply is off, a qualified engineer takes over. Any work on gas pipework or a gas appliance in the UK has to be carried out by a Gas Safe registered engineer. The Gas Safe Register is the official list of businesses and engineers legally allowed to do this work, and you can check anyone's registration on their website or by calling 0800 408 5500. This is not a job for a general handyman or a confident DIYer.
To pinpoint a leak, an engineer works methodically rather than guessing. Common steps include:
- A tightness test on the gas pipework, which measures whether pressure holds steady or drops, showing gas is escaping.
- An electronic gas detector that sniffs out the presence of gas along pipe runs and joints.
- Leak detection fluid brushed onto joints and fittings, which bubbles where gas is escaping.
- A full appliance check to confirm flues, burners and safety devices are working as they should.
The point of all this is precision. A trained engineer finds the exact fault with the right equipment, fixes it safely, and confirms the appliance is sound before signing it off. Detecting and repairing gas is one of the few household jobs where the safe option and the qualified option are the same thing.
How to prevent a gas leak
Most gas problems trace back to an appliance that has not been looked after. A few simple habits keep the risk low.
- Service appliances every year. The HSE advises having gas appliances regularly maintained and serviced annually by a Gas Safe registered engineer. A yearly service catches faults before they become dangerous.
- Fit a carbon monoxide alarm. Choose an audible alarm to the current British Standard and place one near sleeping areas. Test it regularly.
- Keep vents and flues clear. Appliances need air to burn safely, so never block air bricks or vents.
- Use registered engineers only. Always check the engineer's Gas Safe ID card before any work, and confirm it on the register if you want to be sure.
None of this is expensive, and it is far cheaper than dealing with the aftermath of a leak. A serviced appliance and a working alarm cover the two main risks: escaping gas you can smell, and carbon monoxide you cannot.
Where DCI fits in across Cornwall & Devon
It is worth being straight about this. DCI is primarily a water leak detection specialist, and any repair or safety work on a gas appliance or gas pipe belongs with a Gas Safe registered engineer. In a suspected gas emergency, the emergency line on 0800 111 999 always comes first. Once the supply is safe and the urgent danger has passed, our non-invasive gas leak detection can help locate a hard-to-find escape on the utility side, using the same careful, minimal-damage approach we bring to every job. If you are unsure whether your problem is gas or water, our team across Cornwall and Devon is happy to point you the right way.
Frequently asked questions
What does a gas leak smell like?
Natural gas has no smell, so suppliers add a chemical called mercaptan that smells of rotten eggs or sulphur. That distinctive smell is the warning sign. Carbon monoxide is different: it has no smell at all, which is why it needs a separate alarm.
What number do I call if I smell gas in the UK?
Call the National Gas Emergency Service on 0800 111 999. The line is free and open all day, every day. Make the call from outside or from a neighbour's house, not from inside the property where you can smell the gas.
Should I detect a gas leak myself?
No. If you smell gas, do not try to trace it yourself. Leave the property, avoid switches and naked flames, and call 0800 111 999. Locating and repairing a gas appliance or pipe is a job for a Gas Safe registered engineer, never a DIY task.
What are the signs of carbon monoxide rather than a gas leak?
Carbon monoxide is colourless and odourless. Warning signs include a lazy yellow or orange flame instead of a crisp blue one, sooty stains around appliances, and pilot lights that keep blowing out. Symptoms such as headaches and dizziness that ease when you leave the house are another clue.
How do I stop a gas leak happening in the first place?
Have your gas appliances serviced every year by a Gas Safe registered engineer, fit an audible carbon monoxide alarm near sleeping areas, and never block air vents or flues. You can check an engineer is registered on the Gas Safe Register or by calling 0800 408 5500.
Does DCI Leak Detection fix gas leaks?
DCI is primarily a water-leak specialist across Cornwall and Devon. Any work on a gas appliance or gas pipe must be done by a Gas Safe registered engineer. For a suspected gas emergency, always call 0800 111 999 first. Once the supply is safe, we can help with non-invasive utility-side detection.
Worried about a hidden water leak across Cornwall & Devon?
For gas emergencies, call 0800 111 999 first. For hidden water leaks, we find them fast with non-invasive equipment and minimal damage, then give you the report your insurer needs.
Call Dickie on 07822 025 911 No Find, No Fee on residential leak detection (subject to terms)