Not sure this will help, but I hooked up a sensor directly to the burner on the boiler. A simple binary sensor tells me when (and with history_stats, for how long) the burner is firing. When I first set it up I posted about it here.
I’ve since updated that sensor; I now power a relay from the burner whose contacts connect to GPIO pins.
I think what you’re trying to do is sense that the burner has tripped (failed to fire.) So what you’re really looking for is that the controller is powering the burner, but the burning isn’t firing. So, two sensors.
In my own system, I don’t test for this. I get a notification if the boiler temperature drops below it’s lower limit set point, which will tell me pretty quickly if it’s tripped. That hasn’t happened since I started having the boiler professionally serviced annually, so I’ve never seen that notification outside of my initial testing.