Proper Wiring for Condo with Common Boiler

mplsblake

I have a condominium with a single common boiler for the entire 17-unit building and each individual owner/unit has its own thermostat and zone valve (unsure what brand of zone valve). 

I have an old Honeywell mercury 3-wire thermostat I want to replace. Original wires are R-W-B. New round non-programmable heat-only Honeywell CT87K has R-W-Y. Honeywell support said just to insert R-W and taped over B wire. They said give it 2-hours to let the thermostat charge too, with just the R-W wires.

Will this thermostat be compatible with this setup? After I purchased CT87K, another owner said they put in a digital thermostat because of the B wire. Like above, Honeywell said it’s not needed so I should be fine?

If Y is typically for cooling, why is there a Y on the heat only model? Honeywell support said because the parts are used for other thermostats and although installed, doesn’t apply to this one. But then instructions say 3-wire hot-water heat only use R-W-Y. Can I put original B wire into Y terminal?

bburd

Unless there is a problem with it I would keep that mercury thermostat. The new non-programmable non-mercury ones are less accurate and less reliable.

Steamhead

What is the model number (behind the mercury bulb)?

Big Ed_4

That thermostat was used on a power open power closed zone valve . How many wires on your zone valve . We need to know to answer your question correctly .... Two wire drop the B , If it is three wire post the model of the valve , maybe you can use the Y for the old B...

mplsblake

Old thermostat is HB2 T222a 1012 1.

Would B into Y work?