OK - the triple aquastat on your oil boiler (maybe) is wired to allow the pumps to only run after the oil boiler reaches hi limit.I have been reminded in pm that my statement above is not correct - Please note: On a triple A, it would be Low limit. The circs continue to run after it reaches high limit, which it isn't supposed to reach, and continue until the temp goes 10 degrees below the low limit setting or the tstat is satisfied
Since the oil boiler is off its triple aquastat is also dead. -- well should be
Is there a similar triple aquastat on the coal boiler? (IF yes) simply connect c1 to c1 and c2 to c2 on each.
now the aquastat on the 'Live" appliance will control the circ pumps when either proof the c1 to c2 connection.
also connect the T terminals in the same way so the coal boiler sees a call for heat from the load.
but check this with a licensed electrician first. Thats my disclaimer.
This is the "least work" approach - I think there are better but I need to see what control you have on the coal boiler.
NICE PIPING by the way - did you do it?