I'm looking for a manuel, but the search is not finding the model #. The only number questionnable is the 2nd one. could be a 6, a G, or possibly a B. Hard to read. the Serial # TH226371Q. It was circa 1993. It's a gas slide in ?? Maybe drop in ?? I'm not sure I know what the difference is. It seems the thermostat may be the problem, but I need a manuel. Could you help me find one? Thank YOu