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Boier is 1983 Thermo flo 140 BTU unit. have owned since 1998, replaced B&G pump 9 years age with Taco and replaced valve seats in drain valve for all 3 zones. Boiler over heated - found soot blocking flu gas. Cleaned soot form cast iron sections( messy job) flame roll out no longer an issue. Boiler still over heated. Checked L8148E 1265 aqua-stat would not open circuit to gas valve and shut off flame. Aqua stat seemed original, never services since 1998. Replaced with new L8148E 1265 added thermo grease to well wasn't used previously. Boiler burners still not shutting down. measured temps with infrared thermometer sensor well only seeing temps of 160 degrees F measured temps on back side of each cast iron boiler section (5 of them) ranged from 136 to to 168 cool to hot side. Pressure running 4 to 5 pounds over cold set pint of 16 LBS. Are internal cast iron sections restricted air is purged form system out of ideas. any help would be appreciated.