Hydrolevel Hydrostat 3250

I am staging the oil boiler so its a backup heat if coal boiler is unable to keep up with loads, or if coal goes out. Plus oil boiler will be set for a low core temp for DHW coil.

So to make the 3250 just run the circulator to primary loop at XXX degrees, off at XXX i need to ?? 1 use the boiler B1 B2 to run circulator, and switch the Zone/Indirect switch to zone and TT jumped? therefore it only uses the aquastat bulb for cycling the circulator? This unit will be mounted on coal boiler, using its temperature to activate the water from oil boiler into primary loop when needed.

Is am correct with wiring of circulator and TT terminals in 3250 to have it run this way.
heres the link to hydrostat install manual. http://www.hydrolevel.com/pages/pdf_files/hydrostat_3250_instructions.pdf

I read your post 3 different times, and I'm still not exactly sure what you are trying to do. The best I can tell is that you want the circulator between your two boilers to come on when the coal boiler reaches a certain temperature, and if the fire goes out and the boiler cools...you want the circulator to shut off. If that is the case, a L4006B Honeywell would be a very simple and cost effective solution. The Hydrostat is a very nice control, but overly complex for what you are trying to accomplish (in my opinion at least).

Circulator's not between the 2 boilers. 2 boilers suppling a primary side of a pri/sec loop system. water won't flow from oil boiler into primary loop until its called for(staged, off coal boiler water temp ). Oil boiler will always be on, temp control off its own aquastat for DHW(low core temp). Thats where the 3250 comes in, to turn oil boilers primary supply side circulator to primary side of loop, if coal boielr is unable to keep up its own water temp based on heat load, or coal boiler fire is too low(going out) to supply heat to water in primary loop. Independent of oil boilers aquastat contol for its own water temp.

Yes it will also heat the coal boiler, till stoked up, but for a short period won't hurt anything.