Using a fga on older boiler.

[BLOD]

Serviced a balance flue mexico last week.
Everything was looking good - all clean & tidy, BP & gas rate spot on etc.
Took a fga reading and got co/co2 ratio of 0.01
Went back the following morning and took another reading but got 0.0006

The heat ex did need a good cleaning, so could the first high reading be due to particles of dirt stiull in h/ex being blown out from flue ? or something else, maybe faulty analyser ?

Has anyone had this before

thanks blod

 

[CES]

The ratio is usually higher after a good clean due to, as you say, loose particles being displaced.