wilder11354 wrote:t Circulator that feeds return to coal boiler does run 24/7 during heating season so water between the 2 will always be circulating..
Well - you certainly do have a hybrid heating system.
As long as you simply limit the oil boiler on time, by changing the OB call to fire sequence- well your half way thru the season -- let it ride -- a simple wire in as I suggested will do for now
Read what a true primary secondary piping system is - and how to employ hydraulic separation
Don't blame the lowest bidder that you hired and instructed incorrectly