– Thermostat set too low and not calling for heat,
– Thermostat not working,
– Circuit breaker or fuse controlling the furnace is tripped or blown.
– Natural gas or propane control valve is closed,
– Pilot light is out (non-electronic ignition),
– Hot Surface Ignition electronic ignition problem
– Intermittent Pilot electronic ignition problem.
Here’s some Possible Repairs
– Check that thermostat is in heat mode and has appropriate temperature setting
– Try moving dial setting up or down a few degrees
– Clean contacts in thermostat if it is a non-digital type
– Reset tripped circuit breaker
– Replace blown fuse
– Relight standing pilot light
– Troubleshoot hot surface ignition ignition
– Troubleshoot intermittent pilot ignition system.