That last thing you need on a cold winter’s day is a broken furnace. There are some tell-tale signs the furnace will give that will let you know when you should call a repair service right away. If any of the following is happening with your furnace, you will need to get help.
The squealing might start out low, but in a short time, it will get louder and louder. This is a sign that the bearings on the blower motor are wearing out and it is getting harder to spin the blower fan around. You need to get the motor replaced before the bearings burn out and the fan stops running.
No Air Movement
Another reason why the blower motor will stop working is because the run capacitor has burned out. You won’t hear any squealing sounds when this happens, but if you put your hand up against the vent register in a room and you’re not feeling any air flowing through it, you know you need a repair person to come in and check the run capacitor.
Temperature Doesn’t Change
If you adjust the thermostat to make it warmer inside when the temperatures drop and the house doesn't get warmer, you need to have your thermostat checked. The wires inside the thermostat can get loose after years of usage and dust can build up inside the unit. If either of these two things happens, the electrical connection will get interrupted and the inside of the thermostat will need to be cleaned and/or the wires tightened.
Air Doesn’t Get Warm
The furnace sounds like it’s not running, and you don't see any flames inside it, this is a sign that the burners inside the furnace aren’t working properly. Sometimes they just need to be cleaned and other times they need to be replaced.
Pilot Shuts Off
If the pilot light won’t stay on, it usually means that a thermocouple has gone bad or the pilot light needs adjusting. You should call a furnace service company right away to get the furnace working well again.