Tri-Level Home, 3 Zone Boiler heat, Lower Level is FREEZING, No Heat???
If the bottom floor is radiant in the floor heat then you have a thermostat for that zone only. The thermostat is a Model T87 by Honeywell. Also in this zone there should be a thermostatic valve controlling the water temperature to the slab (floor). I would look for a zone valve for this system. If you can't trouble shoot this your self I would call an HVAC co. to do the work so you don't do something you can't fix.