My furnace is not working properly. I shut down the whole electricity and also the switch on my furnice and waiting a few minutes to turn all back on. It will heat up the house and turns off automatically when it reaches my desired temperature setting. But when it needs to start back again it will lite up the fire and turn off about 3 times but never turn on. I have to keep resetting to get the heater to turn in. Changed the filter already and I did see a small light turn off and blink 7 times consecutively.

  • What is the make and model number of the furnace?
    – Tester101
    Dec 28, 2014 at 14:49

3 Answers 3


A red light flashing 7 times typically means the furnace is in lockout mode, which based on your description seems to be your situation.

There are many things that could cause the furnace to fail to light, each of which requires its own diagnostics to determine if it is the problem.

Since it sounds like you don't know much about furnaces, your best bet would be to contact a local licensed HVAC company.

Things that could cause a furnace to fail to ignite include, but are not limited to...

  • Gas off.
  • Electricity off.
  • Clogged burner orifice.
  • Bad flame sensor.
  • Bad pilot assembly.
  • Bad igniter.
  • Bad control board.
  • Bad gas valve.
  • Restricted combustion air supply.

Is there a manual that describes the diagnostic code of the flashing light? If not look up your manual online. Likely the control board has failed and you need to get it serviced.

  • Do you know if that expensive? It turns on but like I said once it hits 75 it turns off and then try's to turn on again but flame goes off and on but never throws air again unless I turn the whole thing back off again.
    – user30093
    Dec 28, 2014 at 1:47
  • I can't guess the cost as I don't know the details of your furnace. Call a serviceman and ask for a quote. Did you identify what the diagnostic code meant?
    – Steven
    Dec 28, 2014 at 3:18

My modulating condensing boiler did that for a while. It turned out to be the flame sensor which is nothing more that a bent rod that comes close to but not touching the burner tube. It was only 3/16 inch from the tube but I adjusted it to be 1/8 inch away and has been functioning perfectly for three years. Check your service manual or google your manufacturer/model and download or purchase one.

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