Why won't the heat turn off?

If your heat doesn't turn off after reaching the set temperature, in other words, the room gets too hot - hotter than the set point temperature. Here are some things that could cause that problem:
1. The thermostat might have been configured wrongly. For instance, if the system is a conventional unit but you configure it as a heat pump. This could cause this to happen.
Verify the kind of system you are using (Heat pump or Conventional unit) and make sure that you wire the system correctly.
2. In some cases, the temperature will go up about 2 to 4 degrees higher than the set point temperature because the residual heat from the furnace causes the temperature in the room to raise till it dissipates, even after heating has stopped. Set the thermostat heating 2 to 3 degrees below the preferred set point if you realise this situation.
3. The thermostat or its wires have been damaged and are not reliably signaling the heating system primary controller. For example, an internal relay sticks and keeps heat on even after the thermostat has sent a signal to shutdown heating.
4. The thermostat is being blocked from properly sensing room heat. That could be due to movement of the warm air supply registers to a new, more distant location, or more often, due to furniture, drapes, or even dust that blocks the air inlet openings around the thermostat that allow it to sense room temperature. This results in the thermostat wrongly sensing the temperature in the room.
5. The thermostat is located on a cold outdoor wall or where cold air blows on it. If your thermostat was not moved and is on an interior wall and in a draft of cold air, this isn't likely to be the cause of the problem you descr