There could be a blockage if you turn on the furnace but no heat is produced. Insufficient airflow caused by clogged air filters may give the impression that the heater is not producing enough heated air.  If the furnace filter's surface is contaminated, replace it right away. Regular furnace filter replacement will help you avoid airflow issues.

Because not all of the hot air produced by the furnace passes through the vents and into your living spaces, closed or blocked vents can also make it seem as though the furnace isn't producing enough heat. Verify that the louvers are open on every vent. Consider removing the vent cover and cleaning it if the louvers are stuck closed.

Check the air filter if the airflow coming from your registers seems low. Airflow can be impeded by a clogged filter. Ensure that all of your air registers are open and unblocked by debris or other objects.

Make sure the system switch is in the AUTO or HEAT position and that the temperature control selector is set higher than the ambient room temperature. If you want the blower motor to run only when the furnace is running, the fan switch should be set to AUTO. If you want continuous airflow, it should be set to ON. By turning the thermostat up to its highest setting, try to activate the furnace.

The furnace's fuel supply should also be open, so check that it is supplied with propane gas or another fuel. Your heating system might run out of fuel if the supply of gas to it is interrupted. If you detect a propane leak, you should leave your house right away and then make an emergency repair call to a nearby HVAC contractor and your propane supplier.

The simplest way to avoid future breakdowns is to get a yearly furnace tune-up. Depending on who you hire, tune-ups can vary, but most involve cleaning your system, lubricating the parts, and checking that the connections are sound. Besides that, technicians keep an eye out for any issues that need to be fixed, like weak pilot lights or cracked heat exchangers. You won't have to worry about your heat going out on the coldest night of the year due to dirty gas valves, loose connections, or malfunctioning parts if you get yearly maintenance.