The most common problem in a furnace, whether it’s an electric-resistance furnace or a gas furnace, is no heat. In the electric-resistance furnace this might be the result of the furnace switch or the main breaker being open, or the thermostat set too low. The homeowner should check the switch, the fuse, the breakers, or the thermostat. Sometimes the blower will run but there’s still no heat. The fuse or the breakers should be checked in that case.
In the case of gas furnace having no heat, the thermostat might again be set too low. The switch, fuse or circuit beaker might be open. The gas might have been shut off for some reason, or the pilot light is off. The homeowner should again check the thermostat, switch, the fuse or the breaker. If the pilot light is out, it should be relit.
Both types of furnaces are subject to cycling on and off too often. In the electric resistance furnace this could be the result of a clogged filter, or a blower that’s not working right. Both of them can cause the furnace to overheat. The homeowner should replace the filter and if there’s something wrong with the blower it should be oiled and adjusted.
With the gas furnace it’s also usually a clogged filter or a problem with the blower and the same remedy applies. But if the blower runs all the time in a gas furnace it might be because the fan switch has been set to continuous circulation mode, or the limit control needs adjusting. The homeowner should reset the switch or adjust the limit control.
The electric-resistance furnace can sometimes not give enough heat. This is usually due to a bad thermostat setting, a broken heating element or a clogged duct or filter. The homeowner should first check the thermostat and reset it if it’s necessary. Then, they should shut off the power and check the fuse or breaker and replace a fuse that’s blown or turn on the breaker. If the fuse blows or the breaker trips when the power is turned back on, the homeowner should call a professional. Any clogged filters should be replaced.