The flame safeguard controller needs to be able to see inside the combustion tube to know what is going on. To do that, it uses a flame sensor that can see whether or not a flame is active. This Honeywell UV Flame sensor sees in ultraviolet light and is used with the Honeywell ultraviolet amplifer. The C7027 sensor mounts on a 1/2 in. sighting pipe by using an integral collar. It can seal against pressures up to 5 PSI when correctly installed.