flame detector

I just typed "boiler flame detector" into google and got about 261000 hits. It's going to take me another few minutes to read them all. They should get you started.

Michael

I can't speak to water tube boilers specifically, a lot of spark ignition systems use flame rectification to sense flame.

When a flame exists, there is ionization of the gas between the ignition rod and the burner. If you apply a positive voltage to the burner, there is a current typically of a few uA from the ignition rod to the burner. If the physically much smaller ignition rod has a positive voltage on it, most of the negative ions are drawn toward it but miss it (much like current flow past the grid or screen in a vacuum tube).

Mark Walsh Rogue Engineering Inc.