CPA1 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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- 4topics
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
Take stable combustion readings at the specified firing conditions and assess each required result.
Flue gas analyser probe placement and sampling plugs
Choose the correct point for combustion sampling or an air-intake check, and reseal the test points afterwards.
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
Combustion Sampling & Reading Errors
Revise the reasoning behind flue gas analyser readings
Work through analyser preparation, the specified sampling conditions and interpretation as separate stages. For each CPA1 question, identify what has actually been measured and what comparison the appliance instructions require. An arithmetic result and a safe-to-use decision are different parts of the exercise.
Check ppm and percentage conversions with the CO/CO2 ratio calculator, then explain the result in context. The combustion analysis guide joins the calculation to sampling, absolute CO readings and the remaining checks.
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%. Assess the ratio, absolute CO and all required checks against the appliance instructions. A low ratio never overrides visible damage, spillage or another failed check.
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
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