I installed the Noma 52-2570-6 programmable thermostat. There are only two wires to connect so there are only two ways to wire it. The furnace comes on but it will not shut down once the desired temp is reached. What can the problem be?

When you disconnect the wires to the thermostat do the furnace shut off?

What is brand and model number of furnace?

I had the same problem with my gas/forced air heater. Does your heat turn off when in the off position? If not, all you have to do is switch the two wires in the thermostat. What's happening is the heater is getting constant power. If the heater turns off when in the off position but doesn't shut off when it reaches the right temp, then its probably a faulty thermosat.