Furnace

The fan limit switch is responsible for turning the blower on and off at the appropriate times. So, when the switch is working correctly, your furnace fan should turn on several minutes after thermostat calls for heat and turn off several minutes after the heat cycle ends.

When airflow through your vents are blocked, the burner of your furnace will shut off, while the blowers continue to run as normal. Over a short period, the fan will turn the air cold or lukewarm at best. Air filters keep the air in your home clean and easy to breathe.

1. Look for a switch inside or near the furnace that turns it on and off. Make sure that it’s set to on.
2. Make sure the gas valve is turned on.
3. Examine the circuit breaker for the furnace.
4. Check the pilot light.
5. Leave the setting for lighting the pilot on for a few minutes after getting it lit.

Most modern gas furnaces can be reset by turning off the power, waiting around 20 seconds, then switching the power back on. Other furnace models may exit lockout after 1-2 hours and attempt to power on again. If your furnace has a pilot light, you may need to relight it following the manufacturer’s instructions.

Actually, you can bypass the flame sensor. the flame sensor is just a way of exposing the voltage on the flame sensor wire to the furnace burner flames. So you can connect the flame sensor wire to a screwdriver and put the screwdriver into the flames.

Signs of a bad furnace flame sensor are:

1. The furnace lights but then shuts down after a few seconds (short cycles)
2. The porcelain on the flame sensor is cracked.
3. The flame sensor is sooty or corroded.