Failure of the burner to ignite can be attributed to several separate (or contributing) factors.
Ignition failure can be due to issues with the supply gases: an insufficiently purged fuel supply, pressure regulators for the air and fuel supplies adjusted incorrectly or simply malfunctioning, or flow restrictions of the fuel and/or air into the burner assembly caused by clogging.
It can also be caused by internal electrical problems, such as faulty contacts and connections in the ignition circuit.
Finally, it may be caused by malfunctioning or failed components, such as the igniter itself, the transformer circuit, or the ignition switch.
Here is a technical note that we wrote: https://ri-gas.com/wp-content/uploads/RIGAS-Glow_plug_modification__light_up_procedure_r2.pdf
Keywords: Rosemount 400A troubleshooting