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Never Changing the Furnace Filter
Clogged air filters are usually to blame when a furnace stops working. Dirty air filters are also hard on blower motors and heat exchangers, so it's a good idea to replace your air filter before there's a problem. It can be hard to remember to check it regularly. That's where an air filter gauge can help; it eliminates guesswork by measuring airflow and telling you exactly when it's time to change your air filter. Plus: You really need to know these 21 air conditioner maintenance and home cooling tips.
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Check the Thermostat
Be sure your thermostat is set to "heat" and at a temperature higher than the temperature inside the house. Thermostat still not working? Here's how to adjust it.