Carbon Monoxide Alarm Going Off

What's happening?

Carbon monoxide is produced when a carbon fuel (gas, oil, coal, wood) burns without enough air, or when the products of combustion cannot escape through the flue. It is colourless, tasteless and has no smell, so an alarm is the only warning you will get before symptoms start. HSE records around seven deaths a year in Great Britain from CO poisoning caused by gas appliances and flues that were badly installed, poorly maintained or short of ventilation, and many more non-fatal exposures. A sounding alarm is not a nuisance to silence; it is a reading. Treat it as a genuine detection until a Gas Safe registered engineer has tested the appliances and proved otherwise.

What usually causes it?

• A blocked or partially blocked flue or chimney: nests, debris, or a collapsed liner
• A boiler, fire or water heater burning rich because the burner or heat exchanger is fouled with soot
• An air vent or airbrick blocked up, covered by furniture, or filled in during draught-proofing
• A flue passing through a sealed void with no inspection hatch, so a joint has separated unseen
• A flueless appliance such as a gas cooker used for long periods to heat a room
• A neighbouring flue terminating close to your window or air vent, pushing its products back in
• A solid fuel stove or open fire sharing a chimney with a gas appliance

Is it dangerous?

Yes, and the danger is that it is invisible. Early symptoms (headache, dizziness, nausea, tiredness, breathlessness, chest or stomach pain, visual problems, erratic behaviour) are commonly mistaken for flu or exhaustion, and you are most at risk asleep, because you will not notice them. If anyone in the house has those symptoms and they ease when you leave the building, say exactly that to a doctor: blood or breath testing has to be done quickly, because CO clears from the blood within a few hours of exposure ending.

Can I fix it myself?

Only the safe response, not any investigation. Turn every gas appliance off, open the doors and windows, and get everyone outside into fresh air. Ring the National Gas Emergency Service on 0800 111 999. Seek urgent medical advice from your GP or A&E if anyone has symptoms, and tell them you suspect carbon monoxide. Do not use the appliances again (not even briefly, not even the hob) until an engineer has tested them. Do not take the batteries out to stop the noise.

When should you call a gas engineer?

After the emergency service has attended, a Gas Safe registered engineer needs to find the cause: a flue gas analyser reading on each appliance, a flue integrity check, and a ventilation calculation for the room. That inspection is the only way to know which appliance was at fault and whether the rest are safe. Book it before you use any gas appliance again, and ask for the combustion readings in writing.

What will the gas engineer actually do?

• Test each appliance with a calibrated flue gas analyser and record the CO and CO/CO2 ratio readings
• Inspect the flue or chimney along its full route, including any hatch into a concealed void, for blockage or separated joints
• Measure the purpose-provided ventilation to the room and compare it with what the appliance needs
• Strip, clean and re-set the burner, injectors and heat exchanger where combustion is poor
• Classify anything unsafe under the industry unsafe-situations procedure and cap or disconnect it with your permission
• Recommission the appliances, re-test, and advise on alarm placement to current standards

If the alarm sounds

1. Turn off every gas appliance, including the hob.
2. Open the doors and windows to ventilate the rooms.
3. Get everyone out into fresh air.
4. Ring the National Gas Emergency Service on 0800 111 999.
5. If anyone has symptoms, get urgent medical advice and say you suspect carbon monoxide.
6. Do not use any gas appliance again until an engineer has tested it.

Questions people ask

Sources & References

1. HSE: Carbon monoxide awareness frequently asked questions
2. NHS: Carbon monoxide poisoning
3. HSE safety bulletin, Gas boilers: flues in voids