Carbon Monoxide Alarm Going Off in Manchester — What to Do Right Now

Quick Answer

What do I do if my carbon monoxide alarm is going off?

Get everyone out of the property immediately — including pets. Don't try to find the source. Once outside, call the National Gas Emergency number on 0800 111 999. Don't re-enter the property until it's been declared safe by an engineer.

Carbon monoxide (CO) is an odourless, colourless gas produced by incomplete combustion. It can kill within minutes at high concentrations — and at lower levels causes symptoms that are easily mistaken for flu or food poisoning. If your CO alarm activates, treat it as a life-threatening emergency. This article explains exactly what to do, what not to do, and what happens next.

What to Do Right Now

Get out. Don't stop to gather belongings, investigate, or open windows — just get out and take everyone with you, including pets. Leave doors open as you go to help ventilate the property, but don't go back in.

Once outside, call 0800 111 999 — the National Gas Emergency Service. This line is free and available 24 hours a day, 365 days a year. They will dispatch engineers to make the property safe.

  1. Get everyone out of the property immediately — don't stop for belongings
  2. Leave doors open as you exit
  3. Call 0800 111 999 (National Gas Emergency) from outside
  4. Do not re-enter the property under any circumstances
  5. If anyone shows symptoms (headache, dizziness, nausea), call 999 for an ambulance immediately
  6. Once the property is declared safe, call Next Gen Boilers on 07305 687 331 for a Gas Safe inspection

Warning: NEVER re-enter the property after a CO alarm until it has been checked and declared safe by a Gas Safe registered engineer. Do not try to ventilate, find the source, or reset the appliance yourself.

Symptoms of Carbon Monoxide Poisoning

CO poisoning symptoms include headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion. Symptoms are often mistaken for flu — the key difference is that CO symptoms typically improve when you leave the property and worsen when you return.

If multiple people in the same household have similar symptoms simultaneously, CO poisoning should be strongly suspected. Call 999 for an ambulance immediately.

What Causes Carbon Monoxide from a Boiler?

Boilers produce CO when they burn gas with insufficient oxygen — a condition called incomplete combustion. This can be caused by a blocked flue preventing exhaust gases from escaping, a cracked heat exchanger allowing combustion gases to enter the water circuit, a poorly maintained burner, or inadequate ventilation in older open-flued appliances.

This is precisely why annual boiler servicing is so important. A Gas Safe engineer checks flue integrity and combustion performance at every service — catching potential CO risks before they become dangerous.

After the All-Clear

Once the Gas Emergency Service has attended and declared the property safe, you'll need a Gas Safe engineer to investigate the underlying cause and carry out any necessary repairs before the appliance is used again. Next Gen Boilers Ltd provides this service across Manchester, Salford and Greater Manchester — call 07305 687 331.

Frequently Asked Questions

Can a CO alarm go off falsely?

CO alarms can occasionally alarm due to very low levels that don't present immediate danger, or due to a faulty sensor (particularly in older alarms). However, always treat a sounding CO alarm as real and evacuate — the risk of assuming it's false is too high.

Where should a CO alarm be positioned?

CO alarms should be fitted in every room containing a gas appliance, on every floor of the property, and within 3 metres of each sleeping area. They should be at head height — CO is slightly lighter than air.

How often should I replace my CO alarm?

Most CO alarms have a sensor life of 5–7 years. Check the manufacturer's recommendation on your specific alarm — many include an expiry date. A CO alarm past its use-by date may not detect gas reliably.

Do I need a CO alarm if I have a combi boiler?

Yes. All homes with any gas appliance should have a CO alarm. Since 2022, UK law requires CO alarms to be fitted in all privately rented homes in any room containing a fixed combustion appliance. We strongly recommend fitting one regardless of your tenure.

Can my boiler pass a service but still produce CO?

A properly conducted Gas Safe service checks combustion performance and flue integrity — but it's a snapshot in time. Component condition can change between services. Keeping your CO alarm in good working order is an essential additional safeguard, not an alternative to annual servicing.

Need emergency boiler help in Manchester or Salford? Call: 07305 687 331