The most common reasons why heaters fail have to do with neglected maintenance, ignition and pilot control issues, wear and tear, dirty filters, and issues with the thermostats. While there are dozens of reasons why heaters stop working, these are among the most frequent.
Before calling a repair professional for the heater, it's wise to check the switch off to the heater and the circuit switch in the breaker box. Many times, repair pros show up to find that the switch off near the unit has been pulled, turning the heater off, or that the circuit has merely tripped, and all they have to do is reset it. Checking those items before contacting a pro saves the cost of a repair call.
Replacing filters in the furnace is an important step in maintenance. Clogged filters force the furnace to work harder to send warm air around the house, and it operates less efficiently and wears out more quickly. Wear and tear is a normal part of aging for an appliance, and bearings and belts deteriorate over time, leading to air flow issues and insufficient heating control.
The heater may not be turning on because the intermittent pilot or the hot surface ignition isn't working. The problem could also be the thermostat, which is responsible for signaling the heater to turn on.