In article ,
cynic writes:

The cold air is still mixed with the flue gases at that point unless a
long probe is used, I used to cover the flap during the temperature
measuring period. There is also the matter of dwell time to allow the
temperature probe to stabilise even with correct immersion in the flue
gases. My electroninc analyser could take up to 3 or 4 minutes before
it stabilised. Oddly enough the old dial thermometer in conjunction
with a Fyrite wet CO2 analyser and slide rule was quicker and I felt
more reliable.

Also, was the boiler fully up to temperature?
If it's still cold, you'll get amazing efficiency reported;-)

--
Andrew Gabriel
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