I have an old thermostat as you can tell by the model number. We recently had to change the leader wire and it worked for a day (but not too great) and now it doesn't work at all. The thermometer reads 75 but the heat doesn't even kick on when we raise it to 85. Is it ready to be buried or can it be salvaged?

We recently had to change the leader wire

Ok you got me what is the leader wire.

I guess that's what it called. The wire that I'm talking about is the one that leads from the boiler to the thermostat itself

The thermostat wire.

If the wire is good and the thermostat does not work then the thermostat is bad. I would check the thermostat with a meter before I would condem it. Usually those old thermostats last forever. Try jumping the two wires together to see if the unit will run.