Narrative:

I discussed takeoff performance with dispatcher prior to leaving hotel. Arriving at airplane I ran several takeoff data messages to verify how much weight we could depart with. Flaps 10 bleeds off provided the greatest weight. Upon receipt of final weights; we were less than 100 lbs heavier than planned; however we could not get any takeoff data despite being below origin max value. Called dispatch and together we were able to discover our new max weight which was about 300 lbs below our current weight. We taxied out and I kept my eye on our weight because I didn't want to block things up at the end if we were still too heavy. My first officer queried me on the bleeds off set up. I told him the left bleed would be off; APU bleed on and right bleed on then at before takeoff final items he would close right bleed. I failed to tell him the isolation valve needs to be closed. He is still relatively new; on probation. I was so preoccupied with the takeoff weight and burning the extra gas. I never noticed the isolation valve. For to he had the engine bleeds off and APU bleed on as required but the isolation valve stayed in the open setting. As pm; I discovered the error when reconfiguring the bleeds after takeoff. I told him of our error and took full responsibility for leading him down the wrong road with my discussion of leaving the APU running and turning off the #2 bleed before takeoff.

Related reports:

Google
 

Original NASA ASRS Text

Title: B737 Captain reported that the isolation valve was inadvertently left open during a bleeds-off takeoff.

Narrative: I discussed takeoff performance with Dispatcher prior to leaving hotel. Arriving at airplane I ran several takeoff data messages to verify how much weight we could depart with. Flaps 10 bleeds off provided the greatest weight. Upon receipt of final weights; we were less than 100 lbs heavier than planned; however we could not get any takeoff data despite being below origin max value. Called Dispatch and together we were able to discover our new max weight which was about 300 lbs below our current weight. We taxied out and I kept my eye on our weight because I didn't want to block things up at the end if we were still too heavy. My FO queried me on the Bleeds Off set up. I told him the left bleed would be off; APU bleed on and right bleed on then at Before Takeoff final items he would close right bleed. I failed to tell him the isolation valve needs to be closed. He is still relatively new; on probation. I was so preoccupied with the takeoff weight and burning the extra gas. I never noticed the isolation valve. For TO he had the engine bleeds off and APU bleed on as required but the isolation valve stayed in the open setting. As PM; I discovered the error when reconfiguring the bleeds after takeoff. I told him of our error and took full responsibility for leading him down the wrong road with my discussion of leaving the APU running and turning off the #2 bleed before takeoff.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.