The older burners usually don't have a post purge cycle, which helps to cool the nozzle and prevent coking. Also, newer burners have a solenoid operated quick cutoff valve at the pump to prevent post shutdown dripping at the nozzle.
The sensors in the combustion test equipment need to be changed on a regular basis. I'm not sure what the shelf life is, but they go bad even with non-use. The some sensors can be changed in the field, some have to go back to the factory. When a sensor is changed the unit needs to be recalibrated, usually with a test gas.
Tony