Date: 201807
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Night
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
ATC / advisory: TRACON ZZZ
Aircraft component: Pressurization System
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Troubleshooting
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: Prior to this flight we had operated [a] flight on the same aircraft. Once parked at the gate after completing [the previous] flight one of the flight attendants informed me that a passenger has expressed concern about one of the windows and thought I should have a look at it. After all the passengers had deplaned I went back to have a look at the window at seat 20D. It appeared that the seal on the outside of the window was coming out so I called maintenance control to write up the issue. The maintenance controller informed me that mechanics were already on their way out to the aircraft to do a service check and that they would deal with the window as well when they got there. After the mechanics showed up and looked at the window they informed me that they would need to check to make sure it was within limits and then do a pressurization check on the airplane. After a few more minutes the mechanic told me that they were ready to do the pressure check and suggested that we get off the airplane otherwise we would be stuck in the plane for the whole time they were doing the check. So at this point the First Officer (FO); both flight attendants and myself decided to get off the airplane. The check took approximately 20-30 minutes to complete and once they were finished the mechanic told me that it had passed the test and that they would just have to wait for an engineering authorization before they could sign off the logbook. Once the mechanic got the engineering authorization they signed off the logbook; told us we were ok to start boarding and left the aircraft. At this point [the] FO and I got back on the aircraft and started performing our pre-flight duties. Once our preflight was complete and all the passengers were boarded we pushed from the gate approximately 40 minutes after scheduled departure. We taxied to Runway 34R as normal and were given takeoff clearance. Our clearance had us on the ZZZZZ1 departure; I was the pilot flying and [the] FO was pilot monitoring. Right around the next waypoint on the departure; as we were passing through approximately 11;000 ft MSL we received a CABIN ALTITUDE HI EICAS message. We both performed our memory items; donning our oxygen masks and establishing communication. I told [the] FO to inform ATC that we needed to stop our climb and would need a descent back down to 10;000 fee t. ATC cleared us back down to 10;000 feet and we descended. At this point I gave control of the aircraft and radios over to [the] FO and I pulled out the QRH to begin running the QRC for CABIN ALTITUDE HI. After completing CABIN ALTITUDE HI QRC I decided that an emergency descent was not necessary since we were already at 10;000 feet. I this point because I was unsure of the reason for the EICAS warning and having the window issue in the back of my mind I decided that the safest course of action was to notify ATC and return to ZZZ. I instructed [the] FO to request vectors back to Runway 34R. While [the] FO was doing that I called the flight attendants to inform them of the situation and let them know we were returning to ZZZ. After talking to the flight attendants I made a PA to the passengers also letting them know that there was a mechanical issue and that we would be returning to ZZZ. Once I had completed me PA I sent an ACARS message to Dispatch also informing them of the emergency and our plans to return. The dispatcher replayed saying something like 'ok; do whatever you need to be safe'. Once all communication was complete I started setting us up for our return. I loaded the approach in the FMS and got landing speeds from the checklist and then backed them up with landing data via ACARS. Once everything was setup I took the aircraft back and we resumed our roles as pilot flying and pilot monitoring. We received vectors to the ILS for Runway 34R and made successful landing. After landing we taxied to and parked at [the] gate. We were met at the gate by the same mechanic that had performed the pressuretest prior to the flight and he seemed to already know what the issue was. It was not until we were back on the ground in ZZZ that we realized that the reason for the CABIN ALTITUDE HI EICAS was due to the fact that the pressurization control mode selector knob had been left in the MANUAL position rather than the AUTO position. Once we were back in the gate I called SOC to talk to the dispatcher and the chief pilot to notify them of what had happened and to see what reporting needed to be done. The on-call chief pilot instructed me write it up in the logbook which I did. The dispatcher then informed me that we would be switching aircraft and taking [another aircraft]. After switching aircraft we departed for ZZZ1 again and completed the flight without further incident.


Second narrative: [Report narrative contained no additional information.]


Synopsis: EMB-175 flight crew reported a loss of pressurization due to the misconfiguration of the pressure controller following maintenance testing.