spill sw shutdown

Got a call from an old customer today that her boiler was not working w/m gas unit standing pilot. Pilot was lit but burner would not come on ,gave it the usual once over, in general it looked ok but whoever installed it did a sloppy job piping and wiring. jumped thermostat and checked for power at valve 0 volts went to spill sw and found it open so I reset it and boiler lit off......wondered why it went off so I lit a match and was suprised to find it blew it out as well as the water htr did then I opened a window in the basement and it still was blowing it out..Water htr and boiler are common vented into a 6 in smoke pipe 2 ft long then go into a 3 by 9 rect. duct then disappear behind a finished wall and into a chimney...Chimney is an exterior chimney with tera. lining and is apprx 30 ft high droped a lite down and saw no blockage however there is turns and bends at lower end I was unable to inspect ....It was getting dark so I shut down both units and called my chimney man for A.M. appointment to check further...I did go get them a co det. as well as asked who installed unit..so happens he has no lic...house is 60 yrs old with finished basement make up air is not perfect..... looking for thoughts