If you smell gas or suspect a leak, HSE and National Gas both say to call the free National Gas Emergency Service on 0800 111 999, open doors and windows and shut off the gas at the meter if you know how.

Call the National Gas Emergency Service

National Gas says that if you smell gas or suspect a leak you should call the National Gas Emergency Service on 0800 111 999, which is open 24 hours a day and free to call. It says to use the same number to report a gas or carbon monoxide emergency, or if a gas pipeline has been struck, even if no gas leak has occurred. HSE’s guidance for home owners gives the same number. National Gas notes that calls are recorded and may be monitored, and that British Sign Language users can use SignLive to contact the service free of charge. This guidance comes from bodies operating in Great Britain.

What to do straight away

National Gas says that in an emergency you should not smoke or light matches, should not turn electrical switches on or off, should open doors and windows, should turn off the meter at the control handle unless the meter is in a cellar, and should call the emergency number. HSE says that if you suspect a gas leak you should call the emergency number, open all doors and windows and shut off the gas supply at the meter control valve if you know where it is.

If you suspect an appliance is unsafe

HSE says it is illegal for anyone to use a gas appliance if they suspect it is unsafe. Turn the appliance off and do not touch it until it has been checked by a Gas Safe registered engineer. National Gas lists signs of a faulty boiler: soot around the appliance, a yellow or orange weak flame instead of a blue one, and a pilot light that blows out easily. In rented homes it advises speaking to your landlord about annual servicing and asking for a copy of the safety certificate.

Carbon monoxide: warning signs and response

National Gas lists symptoms of carbon monoxide poisoning as nausea, light-headedness, headaches, shortness of breath, dizziness and sleepiness, and says it can be fatal. If a carbon monoxide alarm sounds or you suspect a leak, it says to stop using all appliances and switch them off, open doors and windows, and evacuate the property immediately. Then call the National Gas Emergency Service on 0800 111 999 or the HSE Gas Safety Advice Line on 0800 300 363, and do not go back in until you have been given advice. It also says to seek immediate medical help because you may not realise you have been affected, and that going outside into fresh air does not treat exposure by itself. This is not medical advice; ask for help urgently.

Alarms, servicing and hiring the right engineer

HSE strongly recommends carbon monoxide alarms as one useful precaution but says they are not a replacement for regular maintenance and safety checks. It says an alarm should comply with British Standard EN 50291 and carry a British or European approval mark, such as a Kitemark, and be installed and maintained according to the manufacturer’s instructions. HSE strongly advises that all gas appliances, flues and pipework are installed, regularly maintained and serviced at least annually by a Gas Safe registered engineer, and says never to block ventilation and to keep flues clear. Anyone employed to work on gas appliances in a home must be Gas Safe registered and competent in that area of gas work, which is shown on the back of the engineer’s ID card.

FAQs

Should I call my boiler engineer first if I smell gas?

National Gas and HSE both give the National Gas Emergency Service number, 0800 111 999, as the number to call for a suspected gas leak. Contact your engineer afterwards for repairs and checks.

What if I hit a gas pipe during building work?

National Gas says that if you or your builders have hit a gas pipe, you should call the National Gas Emergency Service on 0800 111 999, day or night.

Can I keep using the boiler if I only suspect a fault?

HSE says it is illegal to use a gas appliance if you suspect it is unsafe. Turn it off and have a Gas Safe registered engineer check it.

Bottom line

The guidance is consistent: call 0800 111 999, open doors and windows, avoid flames and switches, and shut off the gas at the meter if you can do so safely. Do not use an appliance you think is unsafe until a Gas Safe registered engineer has checked it, and fit and maintain a carbon monoxide alarm. This is general safety information, not medical or engineering advice.

Sources

This guide draws on the following primary sources, current as of 20 September 2026:

• National Gas, “Emergency Contacts”
• Health and Safety Executive, “Domestic gas: frequently asked questions”

Related guides

Best Boiler Deals is an independent guide. We may earn a fee from some links; this never affects what we write. This article is general information, not regulated advice on any specific installation — always confirm the details with a Gas Safe registered engineer.