The warning signs of an unsafe gas appliance

If you smell gas

Two additional points. First, do not call a plumber or a gas engineer first – the emergency service is faster and it is their job. We handle the repair afterwards. Second, if the smell is outdoors or you suspect a leak in the street, call the same number – it covers that too.

Visual signs on the appliance

On a modern room-sealed boiler you cannot see the flame, which removes the most useful visual indicator. That is precisely why the annual check with a flue gas analyser matters more on a sealed appliance than on one you can look at.

Carbon monoxide: the symptom pattern

CO binds to haemoglobin far more readily than oxygen does, so it displaces oxygen in the blood. The symptoms are non-specific and are routinely mistaken for flu, a virus or tiredness.

• Headaches – the most common early symptom.
• Nausea and vomiting.
• Dizziness and unsteadiness.
• Drowsiness and unusual tiredness.
• Confusion and difficulty concentrating.
• Breathlessness, and chest or stomach pain.
• Visual disturbance.

Individually, none of those points at CO. The pattern is what identifies it:

1. Symptoms improve when you leave the house and return when you come back. This is the single most telling sign.
2. Several people in the household affected at the same time, which a virus would rarely do with this pattern.
3. Pets unwell too. Animals are often affected first, being smaller.
4. Symptoms that track with the heating being on, and appear in the heating season.
5. Symptoms worse in one part of the house.

Alarms

An audible carbon monoxide alarm is inexpensive and it is the only thing that will detect CO before people become unwell.

• One in any room with a fuel-burning appliance, sited to the manufacturer’s instructions – typically at breathing height and a stated distance from the appliance, not directly above it.
• Also worth having near sleeping areas, because CO is most dangerous when people are asleep.
• Check the replace-by date on the casing. Alarms have a finite sensor life, typically seven to ten years, after which they must be replaced – not just have the battery changed. An expired alarm gives false reassurance, which is worse than having none.
• Test it with the test button, which confirms the sounder and the electronics but not the sensor. The date is what tells you about the sensor.
• In rented property in England a working CO alarm is a legal requirement in any room used as living accommodation with a fixed combustion appliance – including oil and solid fuel, not just gas.
• Oil appliances need one too. The idea that CO is a gas-only issue is common and wrong.

The changes that create a problem without touching the gas

A gas installation that was safe can become unsafe because of something apparently unrelated. These are the recurring ones:

1. A new extractor fan, particularly a powerful kitchen hood. It can depressurise a sealed room enough to affect a flued appliance, in the worst case drawing combustion products back down the flue.
2. Blocked-up airbricks or vents, removed because they were draughty. Permanent ventilation is there for combustion air.
3. Replacement windows and draught-proofing, which make a house far more airtight than it was.
4. Boxing in a flue in a loft or a cupboard, which conceals a joint that later separates.
5. Building work that alters a flue route, a terminal position, or the clearance around one.
6. An extension built where a flue terminal used to discharge safely.
7. A new conservatory enclosing what was an external wall with a terminal on it.

This is why a gas safety check assesses ventilation across the whole property rather than appliance by appliance, and why ‘nothing has changed with the boiler’ is not evidence that nothing relevant has changed. Any significant building work in a property with gas appliances is worth having reviewed – see gas safety checks.