I have a weil mclain cg5 boiler. Older style, with Honeywell R8285A controls. I have 3 zone valves, but original owner never had a zone controller... just manually left all zones open. One circulator. Two Tstats.
So to add the Taco, using attached diagram for reference, I believe I just:
1) move tstats to tstat side of taco.
2) connect zone valves to corresponding zone side of taco.
3) connect from R8285 (where tstats used to go to R and G) and connect to Taco Boiler Isolated End Switch. And just let the R8285 do what it always did, control boiler, circulator, exhaust flap, etc...