Captain reported that a pressurization problem resulted in a diversion.

Attributes
ACN	1700207
Time
Date	201911
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Air Conditioning Distribution System
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Total 6
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy Deviation - Procedural MEL

Narrative:

Our aircraft was dispatched with a pitot probe heater system inoperative. (MEL 30-xx). The aircraft also had an eng bleed air prsov write up (MEL 36-xx) which was placarded. We taxied out and took off as normal. Climbing through ~17;000 ft. We turned off the APU and shut down the left pack system as per MEL and utilizing only the right pack for pressure. We received an intercom call from the rear of the aircraft from a deadheading pilot telling us she heard something beneath her feet near the exit row mid aircraft shortly thereafter. Climbing through the mid 20 thousands; the first officer feels pressure in his ears. We ask for a lower flight level (I think 31;000 ft.) than previously cleared (35;000 ft.) to work the problem. This is when we realized the cabin was climbing the same rate as the aircraft. We asked ATC for a lower altitude and received it. The oxygen mask was put on as we did an emergency descent to 10;000 ft. We asked for direct ZZZ and landed. Mechanical failure of pressurization ducting. Although the pitot probe heater had nothing to do with the event it is my opinion aircraft should not be dispatched without this being fixed first. Flying a transport aircraft with people on board and expecting to not fly through a cloud (icing conditions) is preposterous.

Original NASA ASRS Text

Title: Captain reported that a pressurization problem resulted in a diversion.

Narrative: Our aircraft was dispatched with a pitot probe heater system inoperative. (MEL 30-XX). The aircraft also had an Eng Bleed Air PRSOV write up (MEL 36-XX) which was placarded. We taxied out and took off as normal. Climbing through ~17;000 ft. we turned off the APU and shut down the left pack system as per MEL and utilizing only the right pack for pressure. We received an intercom call from the rear of the aircraft from a deadheading pilot telling us she heard something beneath her feet near the exit row mid aircraft shortly thereafter. Climbing through the mid 20 thousands; the First Officer feels pressure in his ears. We ask for a lower flight level (I think 31;000 ft.) than previously cleared (35;000 ft.) to work the problem. This is when we realized the cabin was climbing the same rate as the aircraft. We asked ATC for a lower altitude and received it. The oxygen mask was put on as we did an emergency descent to 10;000 ft. We asked for direct ZZZ and landed. Mechanical failure of pressurization ducting. Although the pitot probe heater had nothing to do with the event it is my opinion aircraft should not be dispatched without this being fixed first. Flying a transport aircraft with people on board and expecting to not fly through a cloud (icing conditions) is preposterous.

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.