Asked by: Jianyu Guesdon
home and garden indoor environmental quality

What does it mean when your furnace won't stay on?

Last Updated: 8th March, 2020

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A malfunctioning thermocouple can lose the ability to sense heat from the pilot light, causing it to close the gas valve randomly. With this in mind, check the pilot light if your furnace isn't staying on. If your furnace's pilot light is not staying lit, it could be the result of a bad thermocouple.

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Similarly, you may ask, why does the flame on my furnace keep going out?

Malfunctioning Thermocouple If your furnace pilot light keeps going out, it's likely you have a broken thermocouple in your gas furnace. The thermocouple is a rod that comes into physical contact with the flame in your system. This component will deactivates the gas when the pilot light goes out.

Beside above, what causes my furnace to short cycle? Another common cause of a short cycling furnace is that the furnace itself is overheating and it's turning itself off to prevent damage. An overheating furnace can be caused by restricted airflow. Restricted airflow is often the result of interior vents being blocked, a blocked exhaust vent, or a dirty air filter.

Similarly one may ask, why does my furnace only run for a few seconds?

Air Flow. Air flow problems also causes your furnace to run for a few minutes then shut off. Proper air flow through the burner is important in order for the burner to remain on and not trip a limit thermostat. The burner draws air from either the outside the home or from the surrounding area.

Is furnace short cycling dangerous?

The most common cause of a furnace short cycling is the air filter in the system becoming clogged with dust and other debris. This causes heat to become trapped in the system, forcing the temperature to rise to high levels that potentially dangerous.

Related Question Answers

Aladji Oribe

Professional

Why does my furnace turn off after a few minutes?

A common reason a furnace short cycles is because the heat exchanger, the part that heats your air, is getting too hot due to a lack of airflow. Once the heat exchanger overheats, it trips the high limit switch, which shuts the furnace down to protect it.

Manue Gopfrich

Professional

How do you fix a short cycle furnace?

Short cycle time: 2-5 minutes.
If the furnace gets too hot, the switch shuts down the furnace. A dirty filter prevents a flow of fresh, cool air into the furnace to be heated and dispersed. Without the fresh air, it will quickly overheat. Solution: Change your furnace filter.

Setefilla Overmeyer

Professional

How do you know if you have a bad thermocouple?

If you can't get the flame to light at all, and you're sure the gas is on, there's probably an obstruction in the pilot tube. If the flame lights and goes out when you release the gas control knob after holding it in for the recommended 20 to 30 seconds, that's the sign of a thermocouple malfunction.

Dado Twelmeier

Explainer

Can a bad thermostat cause a furnace to short cycle?

Thermostat Troubles Can Cause Short Cycling
Your thermostat could also cause the HVAC system to cycle on and off rapidly, a process known as short cycling.

Xuping Koppers

Explainer

How do I know if my flame sensor is bad?

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.

Tinguaro Mettke

Explainer

How do I reset my furnace?

How to Find My Furnace Motor Reset Button
  1. Turn off the power to the furnace at the circuit breaker. The circuit breaker is clearly marked.
  2. Lift up the blower compartment cover to access the blower wheel and blower motor.
  3. Look for a small red or yellow button on the side of the blower motor.
  4. Press the reset button down if it has popped up.

Diagne Simoes

Pundit

How much does it cost to replace a flame sensor?

Depending on which furnace repair company you call, you can expect to pay anywhere from $350 to as much as $500 for a new flame sensor, plus the cost of the travel and diagnostic charge.

Taryn Vaidanovich

Pundit

How do I stop my boiler from short cycling?

In a fully automatic central heating system the short cycling of the boiler can be prevented by using the room thermostat/programmer and hot water cylinder thermostat to switch on the electrical supply to the boiler.

A boiler interlock will:
  1. Protect the life of the boiler.
  2. Save you money - and.
  3. Save energy.

Isabela Tellmann

Pundit

How do I stop my boiler short cycling?

Adding thermal mass to the heating system will decrease the burner short cycling and this can be done by adding water volume to the system. A relatively easy way to add thermal mass is adding a “Buffer Tank”. A “Buffer Tank” is simply a tank of water. For buffer tanks, one size does not fit all applications.

Xun Schmidtgal

Pundit

How do I know if my furnace is short cycling?

One sign to watch for is a thermostat problem. If a thermostat isn't measuring heat levels correctly, or isn't connected to a furnace as it should be, it may begin to turn off the furnace at the wrong times. Repair techs are able to check and see if thermostats are triggering short-cycling.

Maysam Funfhaus

Pundit

Can you run a furnace without a filter?

If you run a furnace without a filter for one night, it won't affect your HVAC system detrimentally. However, the longer you run your heating system without an air filter, the more contaminants accumulate inside your heating unit inner mechanisms.

Lourie Brendli

Teacher

Why does my heater start and stop?

A furnace that starts then stops is a common issue also known as short cycling. When the furnace cycles more often than this, short cycling is possible – it may also be possible that extreme temperatures are causing the need for more frequent cycles, or your furnace is undersized or requires additional insulation.

Chiavana Mantuliz

Teacher

What does a furnace flame sensor look like?

A furnace flame sensor is a very basic part of your furnace. It's located on the burner assembly and is just a thin metallic rod. It's usually bent, and it sits just in front of the pilot flame inside the furnace. The sensor is there to confirm that there's actually a fire present when the gas is open.

Odei Estaca

Teacher

Why does my furnace turn on every 10 minutes?

Off and on every 10 minutes is way too much. It's time to replace the thermostat. This resistor coil does fail and causes the thermostat to open and close causing what we call "short cycling" in the trade where the furnace turns on and off as yours is doing.

Mencia Thadeu

Teacher

How do you clean a dirty flame sensor on a furnace?

Once you have removed the sensor, gently rub the metal rod (and nothing else) with a very light grit sandpaper. Remember, you're not sanding down an auto body here, just ridding the sensor of any buildup. Then, use a clean paper towel to wipe clean any dust left behind by the sanding.

Wieslaw Abravanel

Reviewer

How often should you change your furnace filter?

A good rule of thumb is to change 1-2 inch filters every three months, 4 inch filters every six months and 5 inch filters every 12 months. Signs your air filter needs changed: The filter is visibly dirty. Certainly if you can't see the material of the filter itself, it should be replaced.