Vaillant ECOTEC PLUS VU 80 Installation And Maintenance Instructions Manual page 47

If the flue gas value has to be set, proceed as follows.
The adjusting screw (1) for the air index setting is located
under a sealing sticker.
> Break through the sealing sticker.
> Set the CO
content (value with front casing removed) by
2
turning the screw (1).
i
Turn to the left: Increases the CO
Turn to the right: Decreases the CO
> Only perform the adjustment in 1/8 turns and wait
approximately 1 minute after each adjustment until the
value stabilises. For this, always first turn the adjusting
screw in and then turn it out again for fine adjustment.
– The adjusting screw must only slightly poke out of the
casing:
i
On the VU GB 1006/5-5 and VU GB 1206/5-5,
the CO content only changes after approx. 1
2
turn of the adjusting screw (overcoming the
adjustment hysteresis).
> Press the "Cancel" selection button once the settings
have been made.
> Reattach the front casing (¬ section 4.6).
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