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80% trane furnace runs than on shut down it reignites the burner for a few seconds

mburg
mburg Member Posts: 48
in Gas Heating
I have a customer who has a 80% trane furnace it will run and heat the house but after the burner shuts down it will reignite the burner for a few seconds than shut down again. I have replaced the thermostat that didn't help. Any thoughts on what it could be?

Comments

  • Ironman
    Ironman Member Posts: 7,612
    Could it be cycling off on high limit and then back on before satisfying the thermostat?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • mburg
    mburg Member Posts: 48
    That's definitely a thought I checked the temperature rise and it was within the specs so I didn't think anything of it.
  • icesailor
    icesailor Member Posts: 7,265
    Is it the burner and fan coming on or just the fan? Doesn't the fan keep running after the burner shuts off on a satisfied call but the fan continues to run? Because of residual HX heat?

    Is the return big enough to give satisfactory air flow through the return? Is it a system with 100,000 worth of output air with a return of 8" round flex duct? I've seen that.
  • mburg
    mburg Member Posts: 48
    The burner shuts off the fan stays running because of residual heat than the burner turns on again a few seconds after the burner originally shut off runs both the fan and burner for a few seconds than the burner shuts off and the fan runs until the hx cools and shuts off
  • JUGHNE
    JUGHNE Member Posts: 11,310
    That used to be a symptom of heat anticipator problem in old T-stats. But you said you changed the T-stat. Is this upflow or downflow, some downflow had fan control problems.
  • mburg
    mburg Member Posts: 48
    Yeah the heat anticipator was my first thought that's why I changed the stat, but it didn't help. It's upflow
  • GW
    GW Member Posts: 4,892
    are you positive the flame is going to all the burners right away??
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • wogpa67
    wogpa67 Member Posts: 238
    like ironman and gw stated it may be bouncing off of the hi limit. what type of air filter is on this furnace?
  • DZoro
    DZoro Member Posts: 1,048
    How old of a unit?
    Supply and returns appropriate for the furnace? If so, high limit, and don't forget to check HE, crack is possible cause
  • mburg
    mburg Member Posts: 48
    I couldn't get it to do it when I was there but these are definitely some good ideas, I'm gonna spend some more time with it. Thanks for the ideas!

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