Air Inside - Air can get inside a Blumat for several reasons. This happens most often in a gravity system when we forget to fill the res before the water drops below the output port. That can put air in the supply lines and in a very low pressure system, the air can stop water. And if you wait too long to fill the res, the potting mix or soil can dry out enough to suck water out through the Blumat ceramic cone. If this happens, the Blumats at least need to be refilled. If they are dry for very long, they should be re-soaked. A good idea is to have at least one always soaking and ready to exchange in case anything happens.
Air Outside – Air can get on the outside of a Blumat between the ceramic cone and the potting mix if someone bumps hard against a pot or moves it and sets it down too hard. Animals, children, and too-curious friends can cause this. If there is air between the cone and the potting mix, the Blumat will “think” the plant is dry and not turn off. The solution is simple – just push the soil mix down around the Blumat.
Air in Potting Mix – Sometimes big chunks of perlite, hydroton, or small rocks touching the ceramic cone can confuse the sensor making it “think” the mix is dry when it’s not. You can prevent this by putting some moist peat moss or cocoa in the hole before pushing the Blumat in.
Air in Supply Line – Besides letting a reservoir get too low, a hose breaking, or water supply getting accidentally turned off; the naturally dissolved oxygen in water can over time form air bubbles. This isn’t a problem in most places but in some areas this dissolved oxygen presents a big problem. The easiest preventative maintenance for this is to have an on/off valve at the end of the supply line or better, at the far side of a supply loop that goes back to the reservoir or water source. By opening this valve for a few seconds when you suspect a problem or as periodic maintenance, you can easily let the air bubbles out. This will also flush any unwanted sediment out of the lines.