Thermostat and Temperature

Thermostat not set to heat or temperature not set high enough
The thermostat settings may have been changed without your knowledge. Make sure it is set to the desired settings.

Too warm or too cold areas
Warm air rises and cool air falls. If you have a split level or two-story house, you may find it hard to keep the lower level warm in the winter and the upper level cool in the summer. Sometimes furnaces or air conditioners are over sized and may compound this problem because they won't run long enough cycles to keep all areas heated or cooled. However, there are some things you can do to help:

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In the summer, partially close some of the registers on the lower level to force more cooling to the upstairs. In the winter open all of the downstairs registers and partially close some of the upstairs registers. Be careful not to close too many registers and restrict the overall air flow too much.
When the problem is most noticeable, turn the fan switch at the thermostat to on so the fan runs constantly. This may help more in the summer than in the winter because of the drafty feeling created by the air movement. On the average, the cost of electricity to run the fan for 24 hours is about $1. (Carrier's variable speed furnaces will run at lower speeds to eliminate the drafty feeling and lower the electrical cost to about 20 cents.)
Check your attic insulation. If it's inadequate, adding more insulation can make the upstairs more comfortable in the summer and save heating and cooling costs.
Make sure your windows and doors are caulked and tightly sealed to prevent drafts.
If you have a fireplace make sure it has its own source of combustion air instead of using up the heated air from your home. If your home is tightly sealed, and your fireplace uses air from the home for combustion, it can create a negative pressure in the home and cause a down draft through your furnace and water heater flue. Keep the damper in the fireplace chimney closed when the fireplace is not in use to conserve heat and reduce drafts.