Furnace Ignites Then Turns Off – What’s The Problem?

When you try to turn your furnace on, and nothing happens, you know something is wrong. If the air coming out is cold when it should be warm, you should call an HVAC contractor. What happens when the furnace kicks on, blows warm air and then shuts down before the room is heated? There is just as much need to find out what the problem is when this happens as there is when the furnace simply refuses to operate. Not only does your home remain uncomfortable, but the chances of the furnace not working at all are increased if the problem isn’t fixed now.

Here is what we find to be the biggest causes of this on and off cycle, which is referred to as short-cycling.

A Complicated Thing

Your furnace is made up of many complex systems that all work together to ensure you have a comfortable temperature in your home. Many of these are switches that operate in a chain reaction. If one fails, it halts the whole chain of those that come after. There are also many safety features in a furnace that help keep it safe for your family. If the furnace is experiencing problems that could result in a fire, it may fail to ignite properly. Keep this in mind when the frustration hits. Here are other reasons your furnace may be short-cycling. In all cases, it is important that you don’t have anyone work on your furnace that is not trained as an HVAC specialist. Many things in your home lend themselves to DIY; your furnace is not one of them.

#1 Flame Sensor

The flame sensor does exactly what it sounds like, it senses when the flame of the furnace is on and sends a message to the control board to start blowing warm air. If dirt or dust covers the sensor, the flame isn’t detected, and the furnace shuts down. Sometimes all that is needed is a simple cleaning of the flame sensor, but it may also be worn out and need to be replaced.

#2 Flame Rollout Switch

This switch keeps track of how hot the burners are. If air doesn’t reach the burner and then open the flue that releases the heat, the flame rollout switch will shut the furnace down, so it doesn’t get too hot and catch fire.

#3 Pressure Switch

The pressure switch is tripped when enough air flow is sensed for ignition to continue. If something prevents an adequate amount of air flow, the switch won’t operate, and the furnace will cease to continue firing up.

#4 Control Board

This is the brain of your furnace. It receives messages from all the other parts of your furnace. Any disconnect in allowing messages through will prevent the control board from allowing your furnace to work properly. The control board itself may become defective if wires disconnect or fray power will not be sent to run the furnace.

#5 Draft Inducer Motor

This motor is responsible for drawing air into your furnace and through the burner. This causes the pressure switch to react, which sends a message to the control board that all is in order. If this motor fails, the air is not drawn into the furnace, and the process of ignition is halted.

Air Flow

As you can see from the above causes, proper airflow is necessary for a furnace to function at top form. If your furnace is located in a place where it is unable to experience proper airflow above, below, and around it, you will have problems with the furnace operating properly. The best way to find out if your furnace is located in an appropriate place is to have a heating repair specialist come in to check your furnace. While they do a yearly maintenance check, they can also tell you if your furnace would operate better if moved.

Final Words

If your furnace comes on and then shuts off, and you don’t feel comfortable, contact us for an evaluation of the problem. Your furnace serves an important role in keeping your family comfortable. It is essential that any work is done by an HVAC specialist who has been trained to understand how the furnace works. Not only is comfort involved but also safety is as well. If it has been a while since you have had a furnace check-up, have one of our representatives give it a look once over to make sure you won’t be left out in the cold when you most need your furnace to cooperate. Your comfort is our greatest goal here at Howard Air in Phoenix. 

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Feature image: Dmytro Zinkevych on Shutterstock