| 1/00 | Regulating fuel supply |
| 1/02 | Regulating fuel supply conjointly with air supply |
| 1/04 | Regulating fuel supply conjointly with air supply and with draught |
| 1/06 | Regulating fuel supply conjointly with draught |
| 1/08 | Regulating fuel supply conjointly with another medium, e.g. boiler water |
| 1/10 | Regulating fuel supply conjointly with another medium, e.g. boiler water and with air supply or draught |
| 3/00 | Regulating air supply or draught (conjointly with fuel supply F23N 1/00) |
| 3/02 | Regulating air supply or draught (conjointly with fuel supply F23N 1/00) Regulating draught by direct pressure operation of single valves or dampers |
| 3/04 | Regulating air supply or draught (conjointly with fuel supply F23N 1/00) by operation of single valves or dampers by temperature-sensitive elements |
| 3/06 | Regulating air supply or draught (conjointly with fuel supply F23N 1/00) by conjoint operation of two or more valves or dampers (F23N 3/08 takes precedence) |
| 3/08 | Regulating air supply or draught (conjointly with fuel supply F23N 1/00) by power-assisted systems |
| 5/00 | Systems for controlling combustion (F23N 1/00, F23N 3/00 take precedence) |
| 5/02 | Systems for controlling combustion (F23N 1/00, F23N 3/00 take precedence) using devices responsive to thermal changes or to thermal expansion of a medium |
| 5/04 | Systems for controlling combustion (F23N 1/00, F23N 3/00 take precedence) using devices responsive to thermal changes or to thermal expansion of a medium using bimetallic elements |
| 5/06 | Systems for controlling combustion (F23N 1/00, F23N 3/00 take precedence) using devices responsive to thermal changes or to thermal expansion of a medium using bellows; using diaphragms |
| 5/08 | Systems for controlling combustion (F23N 1/00, F23N 3/00 take precedence) using devices responsive to thermal changes or to thermal expansion of a medium using light-sensitive elements |
| 5/10 | Systems for controlling combustion (F23N 1/00, F23N 3/00 take precedence) using devices responsive to thermal changes or to thermal expansion of a medium using thermocouples |
| 5/12 | Systems for controlling combustion (F23N 1/00, F23N 3/00 take precedence) using devices responsive to thermal changes or to thermal expansion of a medium using ionisation-sensitive elements, i.e. flame rods |
| 5/14 | Systems for controlling combustion (F23N 1/00, F23N 3/00 take precedence) using devices responsive to thermal changes or to thermal expansion of a medium using thermo-sensitive resistors |
| 5/16 | Systems for controlling combustion (F23N 1/00, F23N 3/00 take precedence) using noise-sensitive detectors |