Old thermostat was Honeywell 9141 T822c1124 vertical style for hot water baseboards all around, it is run from a boiler in the condo upstairs in boiler room, tried to replace with one that looks exactly the same , says Honeywell for heat only and is vertical with only 2 wires, same as old one but nothing happens when it is connected. it is CT50K, the old one had a mercury thing on top, new one does not. Have tried several now and am at wits end. Thank you

Honeywell says your part number T822C is for cooling. They might be using it as a reverse acting thermostat on that system.

http://customer.honeywell.com/techlit/pdf/69-0000s/69-0548.pdf