UNABLE TO PRESSURIZE. RETURN LAND.

Narrative

DEPARTED BOS AT XA28 LCL ON SCHEDULED ACR FLT. UPON LIFTOFF FROM RWY 22R ACFT WOULD NOT PRESSURIZE. ASKED FOR VECTORS OUT OF TFC AREA TO RUN APPROPRIATE CHKLISTS TO TRY AND SOLVE PROB. NONE OF OUR EFFORTS SOLVED PROB; SO RETURNED TO BOS IN VFR CONDITIONS AND LANDED WITHOUT INCIDENT IN VFR CONDITIONS. UPON INSPECTION OF ACFT; MECHS FOUND LOWER E AND E COMPARTMENT DOOR IN OPEN POS; WHICH WOULD CAUSE THE ACFT TO NOT PRESSURIZE. CAPT; WHO PREFLTED ACFT DID NOT NOTICE OR DISCOVER DOOR OPEN AND IS POSSIBLE COULD HAVE BEEN OPENED AFTER PREFLT BY MAINT OR WAS NOT DISCOVERED OPEN DURING PREFLT. I; MYSELF; RAN THE INTERIOR CHKS OF THE ACFT FOR THE FIRST FLT OF THE DAY AND CHKED THAT MAINT HAD SINGED OFF THE ACFT AIRWORTHY BEFORE THE FIRST FLT OF THE DAY. ALSO; ALL DOOR ANNUNCIATOR LIGHTS SEEMED TO CHK NORMAL AND DID NOT SHOW ANY DOORS OPEN AT THAT TIME OR BEFORE TKOF. WE WERE ADVISED BY MAINT AT THAT TIME THEY FOUND A FAULTY DOOR LIGHT SWITCH FOR THAT E AND E COMPARTMENT DOOR. SO; IN MY ESTIMATION; THIS DOOR OPEN GOT BY 3 POSSIBLE CHKS. HAVING NOT PREFLTED THE EXTERIOR OF THE ACFT; I COULD NOT TELL YOU ABOUT THE DOOR BEING OPEN! THE CAPT DIDN'T CATCH IT ON HIS WALK-AROUND IF IT WAS OPEN AT THAT TIME; AND THE DOOR ANNUNCIATOR LIGHT WOULD NOT SHOW IT TO BE OPEN. I THINK THE PROB WOULD HAVE SURFACED SOONER HAD ALL PEOPLE INVOLVED BEEN PAYING CLOSER ATTN TO DETAIL.