Results 1 to 12 of 12
  1. #1
    Join Date
    Feb 2008
    Posts
    10

    Fan continues to run after burner shutoff

    Lennox G20 forced air gas fired system about 10 yrs old. After the burner shuts down the fan will continue to run forever. Only by cutting power at the furnace will it stop. Fan should shut off about 90 seconds after the burner shuts down, but is adjustable for a longer interval by a jumper. Does this indicate that what Lennox calls the blower control center (BCC) a circuit board, is faulty or is there sensor or bi-metallic control that might not be opening? Problem seems to be getting more frequent.

  2. #2
    Join Date
    Aug 2008
    Location
    Minneapolis
    Posts
    79
    I work for a lennox dealer, call for service and have that furnace heat exchanger inspected. The G20 exchanger failure rate is extremly high.

  3. #3
    Join Date
    Feb 2008
    Posts
    10

    Fan continues to run after burner shutoff

    Hi Therm76,

    Thanks for the reply. I will have the heat exchanger inspected, but why would a faulty heat exchanger cause this problem? The time delay in shutting off the fan after the burner shuts off is apparently controlled by a timer. There is a jumper that can be changed to make the fan-off delay be either 90, 150, 210 or 270 seconds.

    Thanks, Mark

  4. #4
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,785
    Have the heat exchanger inspected.
    And hen you call to set up the appointment, tell them about your fan problem, and the tech can check it out also.


    May have a safety going out.

    Sorry, this is a NO DIY site.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    Aug 2008
    Location
    Minneapolis
    Posts
    79
    Is your air filter clean? Are you using a filter that is to restrictive? The high temperature safety switch may have something to do with your problem. The G20 heat exchanger failure rate is high and you should have the furnace inspected annually due to age.

  6. #6
    Join Date
    Oct 2008
    Location
    Central Oregon
    Posts
    184
    If it was out on high limit, it wouldn't fire up.

  7. #7
    Join Date
    Aug 2008
    Location
    Minneapolis
    Posts
    79
    The high limit is a snap disc. Will cycle burners until temperature limit reached. Homeowner just call for service. therm76 out

  8. #8
    Join Date
    Oct 2008
    Location
    Central Oregon
    Posts
    184
    Oh, that limit. Then there's the manual reset on the blower housing.

    'tis surely true the heat exchangers in the G20's don't hold out as well as others. I just condemned one on Monday. On Friday I did maintenance on another G20 (a '93) and advised the customer to plan replacement before the furnace planned it for him. He said the HX had already been replaced once. I said "oh, ok then". He had an April Aire 2200 filter system so that HX should be good for a while. I adjusted the manifold gas pressure from 3.8" wc to 3.5.

  9. #9
    Join Date
    Feb 2008
    Posts
    10

    fan does not shut off

    I have an annual maint scheduled in about 2 weeks...will see if I can get it moved sooner.

    Problem is intermittent as it had occurred 3 times in a week until last night when it occurred 5 or 6 times. It occurred again this morning the first 2 cycles and has been OK the last several. Filter is changed regularly.


    Thanks for all the input!

  10. #10
    Join Date
    Mar 2004
    Location
    SE Michigan
    Posts
    18,223
    A well placed kick to the side of the furnace does wonders.
    To put the world in order, we must first put the nation in order; to put the nation in order, we must put the family in order; to put the family in order, we must cultivate our personal life; and to cultivate our personal life, we must first set our hearts right.
    -- Confucius

  11. #11
    Join Date
    Feb 2008
    Posts
    10

    fan does not shut off

    I'll give it a thump next time it fails. If a thump stops the fan, what would that tell me?

  12. #12
    Join Date
    Mar 2004
    Location
    Illinois
    Posts
    6,959
    Quote Originally Posted by aaronml View Post
    I'll give it a thump next time it fails. If a thump stops the fan, what would that tell me?
    That it's suffering from "fonzarello" syndrome.

    Dangerously close to Diy...sorry.

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