Why does my furnace fire up then shut off after a minute or so?

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My furnace just recently started firing up only to shut itself down after a couple of minutes. Does anyone know what might be causing it to do this? Could this be a dangerous situation?
  18 answers
  • Need some more information. Is it just the flame that starts and stops? or is it the blower doing that. Also what kind of furnace do you have? Oil, or gas? Normally on both oil and gas if the flame is turning on for a short while, then turning back off, only to come back again in a few min and the fan is still running all the time. This can be a few things, most of which are simple. If the filter is blocked and really dirty, change it, If you have an AC coil connected it could be blocked with dust and dirt. If your return grills are blocked by linens or the back of a couch preventing the air to return back to the furnace, that can cause this. Lastly it can be a defective high limit switch. What in effect is happening. There is A control on the furnace that regulates how hot the furnace becomes. On older furnaces this is controlled by a small device that has a dial shaped device on the front. AS the furnace warms up this dial turns on the blower. If the air flow is blocked and the furnace continues to become warmer and warmer, as the heat its making is not being taken away by the blower fan a 2nd switch comes into play and turns off the oil or the gas part of the heating side of the furnace so it does not over heat. This is the device that is causing this issue. But if the air flow is blocked somewhere its doing exactly what its supposed to do. This prevents fires, and cracking heat exchangers. It will be OK to let this happen over night, but you do not want this to continue more then over one evening as it can stress crack the heat exchanger causing it to fail thus requiring an new furnace altogether. In the interim check the filter to assure its clean. If its one of those high efficiency units or a washable type. Remove it and see if it stops the issue. The only other thing that can cause this is a faulty blower motor. If the fan is not working at all, you will need to get the furnace evaluated. It can be a faulty motor or switch that controls it. It all depends upon the type of furnace, its age that you have.
  • Sheryl Dunham Sheryl Dunham on Oct 17, 2014
    probably needs a new thermo-coupler...furnace man repair :(
  • Pjallen2002 Pjallen2002 on Oct 17, 2014
    Make sure the filter is clean and not blocking air flow
  • Billie Wilson Billie Wilson on Oct 17, 2014
    Make sure your venting is clear aka chimney.
  • Kathy Kathy on Oct 17, 2014
    Ours did that and we had we had a bad flame sensor. The sensor quit working so the furnace can't tell that it is lit so it lights and shuts off...It can't see that it is lit so the furnace thinks that natural gas is pouring into the house and shuts off. It then tries to re-light...this process will go on and on. That is a cheap and easy fix if that is what the problem is .
  • Janinne P Janinne P on Oct 17, 2014
    Also, your thermostat might need repair or replacement.
  • Darlene Hansen Darlene Hansen on Oct 17, 2014
    My retired HVAC husband says you need to have it looked at...something you can't do yourselves. It could be a limit switch problem, a hot surface igniter issue, a flame sensor needing to be cleaned, a pressure switch problem....all of these are issues that could be serious, as was mentioned, with natural gas furnaces. Sorry to be the bearer of bad news but better this news and some others, right? Good luck!
  • Joan Good Joan Good on Oct 17, 2014
    It mean it's either not lighting or not staying lit. It's not hard to do some simple investigation yourself, change the filter, look for any obvious obstructions (animal nests even a spider web in the wrong spot!) check that the gas is actually on and the pilot is lit if there is one! hold the safety switch in and let it try to light. Watch if it gets a flame at all. That's a critical bit of info before moving forward. You can also Google the make and model of your furnace and the phrase "won't light" or "won't stay lit" for other troubleshooting ideas. Some repairs, like a new thermocoupler are easy to do yourself. I swapped mine out for $12, took 10 minutes!
  • Miss Kitty Miss Kitty on Oct 17, 2014
    Thank you all for your input. It's good to know all of these things. I will have my SIL look at it and tell him what you all said. Sometimes he can do furnace repairs if it is just something simple. If he can't, then I guess I will have to call a service man. I appreciate your taking the time to respond.
  • Irish53 Irish53 on Oct 17, 2014
    If you have a oil furnace when was the last time you had the lines vacuumed out. It can be something simple as dirt clogging the feed lines to the burner. If you have too much sediment at the bottom of the oil tank it can be stirred up when oil is delivered. If the burner is running at the time of delivery it gets sucked into the lines and can keep the burner from running
  • Sherry Fram Sherry Fram on Oct 17, 2014
    My friend who is a HVAC installer and repairman says to call the repairman it needs to be looked at.
  • Miss Kitty Miss Kitty on Oct 17, 2014
    Thank you for responding Irish53 and Sherry Fram. I am definitely going to call a repairman. I don't want to take any chances.
  • Jennifer J Jennifer J on Oct 17, 2014
    The copper sensor needs to be cleaned.
  • Jollyroger Jollyroger on Oct 17, 2014
    I had the same problem and it was a thermocouple.
  • Chris J Chris J on Oct 17, 2014
    We had that problem with our furnace, It would make turning on sounds but nothing would happen. We called the gas company who sent the repair guy out. It's called short cycling. He did something with our thermostat and did something to the furnace and it's worked like a champ since then. The gas company said it isn't something that you can fix yourself..
  • So folks understand. The thermocouple is a safety device that allows the gas valve to operate as long as the pilot light is lit. When the pilot light goes out,. It locks out the gas valve and prevents the gas from coming on which without a pilot light could cause an explosion. Has nothing to do with the issue the poster is asking about. But its good to know that people are learning more about their equipment. If its not a plugged filter or a issue with the blower, its time to call a service tech.
  • Tim's Man Blog Tim's Man Blog on Oct 17, 2014
    Good call Miss Kitty.... Everyone here has awesome suggestions, and all are possible causes. However, what you describe can be caused by any number of things, most of which need a professional to diagnose/repair... What you are hearing when you hear it "kick on" is actually just the induction fan which comes on before the gas, to eliminate carbon monoxide hazard. You are perfectly safe in your home though....the fact that it won't come on is actually a good thing, alerting you to something that would be hazardous if it DID come on. Best of luck to you.....I hope it's something cheap and easy!
  • Miss Kitty Miss Kitty on Oct 18, 2014
    I appreciate all the comments everyone has posted. Thank you all so much for taking the time to let me know of all the issues it could be. After reading your comments, I am convinced that I need to have a repairman come here and take care of the problem. I can see that it is probably going to be a much bigger issue than I thought. I'm keeping my fingers crossed that it won't cost me an arm and a leg. :-(
    • Tim's Man Blog Tim's Man Blog on Oct 18, 2014
      @Miss Kitty Keeping my fingers crossed for you too! Hope for the thermocouple, it's probably the cheapest of the fixes. Around $15-$20 for the part, and $150-$200 in labor.
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