This is the worse supply office that i have ever dealt with[ and i am 82 yrs old]the staff is very is so untrained. I have been calling to their office continuously, practically every week from day one almost a year that i have dealt with them.it would take me 3 pages of paper to write every thing that i am experiencing. The latest. Being. I finally got a carry with concentrater after monkeying around for months first time i used it message comes on saying { system hot" and it was. Called office and they said i was holding it to close to my body, which in fact i was carryiing it like a suit case,, no where near my body. Changed batteries, took it out today. Same thing happens. Have to curtail my outing and come home. The thing was so hot it almost burned your hand, answering service gets a hold of supervisor, and me almost sreming muy head off, demanded the bring out some tanks so i could leave the house... so upsetjust one thing after another