DF-520 Installation Pictures
This thread is about the best I've seen for professionally installing the L6006A Honeywell aquastat, which is used as an outfire control for the stoker. It is the farthermost right control on the top of the left side panel of the cabinet. Can be seen in the second picture appearing at the start of the thread. Behind the L6006A aquastat is a tapping in the boiler which will accommodate the "well" needed to install the "A" aquastat.
NOTE: This set-up can only be used with a hot water boiler; not a steam boiler.
The alternative is to use the L6006C aquastat, which straps to the outlet pipe at the top of the boiler.