It's never fun when your furnace stops working, especially when it is in the middle of winter. However, you should take the time to troubleshoot the issues before you call a professional for help. You could either find a simple fix to your problem, or have more information to give to the HVAC technician.
Check Your Thermostat
Thermostats have become even more complicated recently as they have become smarter. While before it was quite clear if a thermostat is on or off, now settings can be buried within menus and you are not quite sure how or why your furnace is turning off and on.
Start by clearing all existing schedules and smart settings that are designed to learn when you are home and need heat. For example, your thermostat may have been switched to an energy saving mode that only kicks the heat on when it reaches very cold temperatures.
Once your settings are cleared, switch the thermostat to a manual mode and see if that gets the heat running again.
Verify Circuit Breakers and Valves
An electrical breaker can be tripped and cause your electric furnace to stop working. Start by looking at the main electrical panel for the breaker going to your furnace and see if it is in the off position. Flip it on and see if your furnace now turns on. For a gas furnace, there are valves that control the gas flowing into the furnace. Verify that these are open.
Look For Air Obstructions
Anything that is preventing air from flowing throughout your vents may give the impression that the heat is not working. First look at the air filter within the air handler. It is possible that this filter is filthy from years of not being cleaned, and the air is simply struggling to get through the filter. You can swap out that old filter for a clean one and immediately see improved air flow.
You should also verify that all vents and dampers are open. Not only can vents be closed at each vent cover throughout the house, but the vents may have dampers that can be closed within the ductwork from your basement. You may have had a contractor in your home recently, and they closed those dampers without telling you because they didn't want dust traveling through your home.
When you perform these basic checks and still can't find the problem, contact local heating repair services for assistance.