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Morten
 
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"Harry Bloomfield" wrote in message
...

A permanently installed flue gas instrument (LED display) measuring CO2
levels indicates 20% with no combustion gases passing up the flue. With
the burner system in operation this level declines to an indicated 9%.


Are you sure it's not measuring O2 ie. Oxygen, that would explain the
figures and they sort of make sense. 20% is normal levels of Oxygen and 9
sound about right when the boiler is running, depending on how the boiler
has been setup.


My immediate response is that the meter is obviously working the wrong
way, if CO2 levels go down with combustion. The instrument is suggested
to be clearly marked that it reads 'CO2'.


If' that is the case then the meter needs calibration, or is connected to a
high flue that stratisfies because CO2 is heavier than the rest of the air.

Does it decrease below 9% when the boiler runs the fan before ignition?


What is the normal level of C02 in the atmosphere as a percentage and
will the instrument be designed to detect the additional amount of CO2
(above the atmospheric normal), or to measure the overall level?


2-3% if I remember correctly...


/Morten




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