I've had a Sensorcon for about two years and had 0PPM during cruise flight, but lately it's 5-10PPM with the heat on. Usually, if I turn the heat off, I can get it down to 0PPM and then if I turn it on again later in flight and mix it with cabin air, it's only 1-2PPM or even back down to 0. Is this indicative of a developing leak? Or is the number so small it's negligible? What would be the next steps? For those with a digital carbon monoxide reader, what do you see in cruise?