In article ,
Jerry writes:

The results I got we

Ambient temp 25.1 deg C
Flue gas temp: 159.2 deg C
Oxygen: 4.6%
Carbon monoxide: 10 ppm
Carbon dioxide: 12.1%
Poison index: .0001 Rat (whatever that is)

It's probably the CO/CO2 ratio (it's about the right value).
If so, figures above 0.004 (IIRC) tend to indicate the boiler isn't
burning gas as well as it should, and figures above 0.008 would
indicate a need for servicing. 0.0001 is a good value.

Gross efficiency: 87.8%
Net efficiency: 93.1%
Carbon monoxide undiluted: 13 ppm (whatever that is)

The data sheet for the boiler only gives the following values:
Smoke No 0-1, CO2 12%, Approx flue gas temp: 165 deg C

--
Andrew Gabriel