After closing the breathing air valve (closed from Friday night till Monday morning) the CO Clear is detecting approx. 9 ppm of CO and both alarms are activated. This valve is installed in front of air purification stages. The refill and filter elements were exchanged last month. Unfortunately, alarms occur every Saturday morning and nobody understands why so high CO concentration occurs with no air supply.
I believe that when the air valve is closed on Friday there may be residual CO in the line, and there may also be a small amount of CO leaching into the line from the air purification stages. I would therefore suggest that a shut-off valve is fitted between the filtration system and the CO Clear.