Narrative:

During taxi out; I had to gate return for a high stage bleed valve failed closed that I discovered during my initial taxi out. I spoke to maintenance control about the issue and they refused to apply MEL 36-xx-a which would have allowed flight in icing conditions. Instead; he insisted on using MEL 36-xy-a disabling the entire left engine bleed system. After much discussion and delay and trying to explain my concerns about how MEL 36-xy-a which locked closed the prsov (bleed valve) limiting our flight altitude to FL250 and to avoid icing conditions; not to mention flying over high terrain on a single bleed source. I explained my concerns to no avail. The only reason that I accepted the aircraft was because I believed it to be a legal dispatch and I could operate the flight safely. Also; I did not want to delay my customers any further.from a systems perspective; this MEL 36-xy-a was unnecessary and provided for many more flight restrictions. Contract maintenance locked out the prsov as called for in the MEL; but after pushback and engine start; I found the left engine bleed valve still open. This necessitated another gate return creating more stress for my customers and crew. The contract maintenance technician made an error in the lock-out procedure and corrected it after gate return.I have [over 30] years flying experience at this airline; [over 15 years] on the 737; and I have had this same high stage valve failure before. There is no reason in my professional opinion that this aircraft could not have operated under MEL 36-xx-a only locking closed the high stage valve.MEL 36-xy-a requires operations avoiding known and forecast icing. When release was amended with this MEL; dispatch advised me that weather was clear with no known; forecast or reported icing conditions.as we approached ZZZ at FL250; we were approaching cloud layers that constituted icing conditions. ATC then reported mod rime icing. We descended to remain clear of clouds and icing. We had to descend to 13;000 feet to avoid all the icing.I know that I hold joint responsibility with dispatch in this regard; but due to the very heavy work load I was experiencing working with maintenance control for this departure; I relied on dispatch for the weather evaluation.

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Original NASA ASRS Text

Title: B737 reported an engine bleed valve problem that resulted in the use of an MEL with restrictions to flight operations.

Narrative: During taxi out; I had to gate return for a high stage bleed valve failed closed that I discovered during my initial taxi out. I spoke to Maintenance Control about the issue and they refused to apply MEL 36-XX-A which would have allowed flight in icing conditions. Instead; he insisted on using MEL 36-XY-A disabling the entire left engine bleed system. After much discussion and delay and trying to explain my concerns about how MEL 36-XY-A which locked closed the PRSOV (bleed valve) limiting our flight altitude to FL250 and to avoid icing conditions; not to mention flying over high terrain on a single bleed source. I explained my concerns to no avail. The only reason that I accepted the aircraft was because I believed it to be a legal dispatch and I could operate the flight safely. Also; I did not want to delay my customers any further.From a systems perspective; this MEL 36-XY-A was unnecessary and provided for many more flight restrictions. Contract Maintenance locked out the PRSOV as called for in the MEL; but after pushback and engine start; I found the left engine bleed valve still open. This necessitated another gate return creating more stress for my customers and crew. The Contract Maintenance Technician made an error in the lock-out procedure and corrected it after gate return.I have [over 30] years flying experience at this airline; [over 15 years] on the 737; and I have had this same high stage valve failure before. There is no reason in my professional opinion that this aircraft could not have operated under MEL 36-XX-A only locking closed the high stage valve.MEL 36-XY-A requires operations avoiding known and forecast icing. When release was amended with this MEL; Dispatch advised me that weather was clear with no known; forecast or reported icing conditions.As we approached ZZZ at FL250; we were approaching cloud layers that constituted icing conditions. ATC then reported MOD rime icing. We descended to remain clear of clouds and icing. We had to descend to 13;000 feet to avoid all the icing.I know that I hold joint responsibility with Dispatch in this regard; but due to the very heavy work load I was experiencing working with Maintenance Control for this departure; I relied on Dispatch for the weather evaluation.

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.