Combustion Performance Analysis revision notes
Using a flue gas analyser — what the CO and CO₂ readings mean and when an appliance is not safe to leave running.
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BS 7967: Flue Gas Analyser Operation & CO/CO2 Ratio
Calculating the CO/CO2 ratio from analyser readings
How two analyser readings become a single CO/CO2 ratio, with worked pass and fail examples.
Combustion and the CO/CO2 ratio (diagram)
Complete versus incomplete combustion, and why the CO/CO2 ratio is used as a measure of combustion quality.
Combustion performance check: an ordered method
The on-site sequence for taking a sound combustion reading with a flue gas analyser.
Combustion performance: what the analyser tells you
How a flue gas analyser assesses combustion and why the CO/CO2 ratio matters.
Flue gas analyser probe placement and sampling plugs
How to identify combustion sampling points on room-sealed condensing boilers.
Flue gas analyser readings glossary
Plain definitions of the readings a flue gas analyser shows and what each one indicates.
BS 7967: Carbon Monoxide Action Levels
Flue Gas Analyser Care and Calibration
In-depth guides for this module
Longer walkthroughs that sit alongside the revision notes.
CPA1 combustion analysis revision guide: CO, CO2 and ratio decisions
CPA1 is a decision process: suitable zeroed analyser, correct sample point, stable appliance, then ratio = (CO ppm ÷ 10,000) ÷ CO2% — at or below 0.004 is the usual revision limit — and a clear safety action when a reading fails. The ratio never overrides visible damage, spillage or high CO.
How to gas rate a boiler: meter reading, formula and worked example
Time a known meter volume, scale it to m3/h, apply calorific value and compare heat input with the appliance rating.
More gas modules
Every module has its own revision notes and question bank.