Our NNU had this problem with SLEs, cured by setting the 850s to 0.0 offset.
As this is a service job, you need to make sure the modified humidifiers are labelled and don't drift into other areas where this setting would cause other problems.
(I don't like this inflexibility in the 850. I preferred the old 730 that you could set to suit the equipment and conditions prevailing. This is an advantage of the new Intersurgical humidifier - it has a choice of auto and manual settings.)
