I'll have to research the Ergomax! Thanks for the information.
Interesting idea about the flow switch, but I wouldn't want the stoker to run everytime hot water is used. I thought about using a L6006C surface mount on the hot water outlet of the coil pipe, and have R-W wired in parallel to the timer. Set the L6006C to 170F, and if the hot water drops below 160 it will turn on the stoker assuming water is flowing. This doesn't work without hot water flowing... Would need a flow and temp sensor.
The switch would be a simple solution, but have no way to get a wire up to the second floor bathroom.