The leakage test checks whether or not the main gas valves are leakproof. For this purpose the gas pressure of the supply is analysed. As leakage test section (space between the two main valves) burns empty whenever the burner is switched off, this part is usually pressureless at start-up (gas pressure > min = 0). This is checked by BurnerTronic. At this point, main gas 1 opens briefly and gas flows into test section (gas pressure > min switches from 0 to 1). This pressure must remain constantly at least while leakage test period (P 311) is running. The leakage test is considered complete then. If leakage test section is not empty at start-up (e.g. resulting from a previous fault shutdown), main gas valve 2 opens first. The leakage test line is then ventilated (depending on the plant, either in the combustion chamber or through the roof –During leakage test period section is checked whether it remains pressureless or not. The leakage test takes place prior to ignition.