The standard for Vented, ANSI Z21.50 / CSA 2.22, has been revised and the 9th Edition was published June 2019. Within this 9th Edition is the inclusion of a newly defined ignition source: the on-demand system.
The on-demand system is an ignition system that is placed into operation for a predetermined amount of time, once the main burner gas valve is operated, and extinguishes the pilot if the main burner flame has not been proven or the main burner gas valve does not open during this predetermined amount of time.
The standard requirements now include the on-demand system to include, but not limited to, maximum safety control timings for pilot flame-establishing, flame failure response and flame failure re-ignition. Revised standard requirements also have updated the instructions and markings required to include the on-demand system.