Carbon monoxide testing

Alarms and testing are not the same thing

A carbon monoxide alarm is essential and every property with a fuel-burning appliance should have one. It is also, by design, a last line of defence: it sounds when CO has already reached a concentration in the room.

Combustion analysis is different. It measures what the appliance is producing at the flue, which tells you whether it is burning correctly – before anything reaches the room, and regardless of whether the flue happens to be containing it today.

When testing is worth having

• As part of every annual service, which is when we do it as standard.
• After any building work – an extension, new windows, draught-proofing, a new extractor fan, a blocked-up airbrick. All of these can affect a flued appliance without anybody touching it.
• After buying a property, where the history of the appliances is unknown.
• Where there are symptoms – headaches, nausea or drowsiness that improve when people leave the house, affecting more than one person or a pet.
• Where an alarm has sounded, even once, and even if it stopped.
• Where there are visual signs – yellow flames, soot marks, excessive condensation when the appliance runs.
• In a rented property, alongside the landlord’s obligations.
• Where an appliance is old or has not been serviced for some years.

What the test involves

1. Inspect before measuringFlue route and terminal, ventilation provision, clearances, and whether anything has changed since the appliance was installed.
2. Run the appliance to temperatureCombustion readings from a cold appliance are not representative.
3. Analyse the flue gasesWith a calibrated electronic analyser. The ratio of carbon monoxide to carbon dioxide is the key figure – it is a direct, objective measure of combustion quality.
4. Check ambient CO in the roomWith the appliance running and, where relevant, with extraction running too.
5. Test the interactionA powerful extractor in a sealed room can depressurise it enough to affect a flued appliance. This is checked with the extraction on, which is the condition that actually occurs.
6. Check flue integrityAlong the accessible length, including inspection hatches where they exist.
7. Record the readingsYou get them on paper. The year-on-year trend is what shows an appliance drifting.

What the readings mean

The important output is the CO to CO2 ratio. A correctly burning appliance produces very little carbon monoxide relative to carbon dioxide; one burning badly produces progressively more. Industry thresholds define where an appliance becomes unsafe, and manufacturers specify acceptable ranges for their own equipment.

The value is not only the pass or fail. It is the trend:

• A ratio that has crept up over three services is telling you something is degrading, well before it becomes a problem.
• A rising flue gas temperature year on year means the heat exchanger is fouling.
• Ambient CO detected in the room with the appliance running means products are entering the space, which is a different and more urgent finding.
• A change when extraction is switched on points at a ventilation interaction rather than an appliance fault.

Keep the tickets. They are the objective record and they are worth far more as a series than individually.

What happens if we find something

Where an appliance is producing CO at an unsafe level, or where products are entering the room, it is classified according to the industry procedure, explained to you, and – with your permission – turned off and labelled until it is put right. Where a situation is immediately dangerous, the relevant emergency provider is notified.

More often, what we find is an appliance that is drifting rather than dangerous – burning less cleanly than it should, which is costing you fuel and heading somewhere worse. That is a service and adjustment rather than a crisis, and it is exactly what annual testing exists to catch.