The on-site order for a combustion check, from preparing the analyser to recording the result and resealing the test point.
Use this sequence alongside the appliance and analyser instructions. A hazardous atmosphere, occupant symptoms or an instrument warning interrupts the routine: stop and take the appropriate protective action before continuing any investigation.
- Check the analyser's calibration certificate is in date. Calibration is commonly every 12 months, at the interval the manufacturer sets; an out-of-date analyser cannot support a safety decision.
- Check the water trap is empty, the filter is clean and dry, and the probe, hose and connections are sound and leak-free.
- Switch on outside in clean air, away from the flue and vehicle exhaust. Let the analyser finish its warm-up and purge countdown and zero. Clean outdoor air reads about 20.9% oxygen; investigate an unexpected fresh-air reading before using the instrument.
- Run the appliance until it is warmed through, at the firing rate its instructions specify, normally maximum (full) rate, with the casing as specified.
- Where the appliance has a designated flue-gas sampling point, use it with the specified probe depth and seal. Do not substitute the air inlet, a gas-pressure point or an improvised location. If there is no designated point, obtain the manufacturer’s or recognised appliance-specific sampling procedure before testing.
- Allow normal readings to stabilise under the specified conditions. Stop and follow the appropriate procedure for excessive gas levels, instrument warnings or implausible readings; do not wait for a dangerous result to settle into range.
- Record the actual O2, CO, CO2 and CO/CO2 ratio. Compare each with the manufacturer's data and the appliance's ratio limit; the ratio and the CO concentration are separate checks.
- Where the instructions require it, repeat at minimum rate once combustion has stabilised at that rate.
- Remove the probe, then refit and check the sampling-point plug.
- Act on the result. Within limits, with the other checks passed: record the readings; the appliance may stay in service. Outside limits: validate the reading, then follow the manufacturer's procedure to find and correct the cause. Do not adjust outside the permitted settings to pull the figure down. After any remedial work, repeat the analysis under the same conditions and record that reading.
- Complete the analyser’s prescribed fresh-air shutdown purge, then drain collected condensate and maintain the sample path as instructed.