Furnace fan blower keeps running even when thermostat is off

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  #1  
Old 03-31-11, 11:23 AM
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Furnace fan blower keeps running even when thermostat is off

I recently had a furnce repair done because the flame would ignite, run for several seconds, and shut off because the fan would not come on. It ran normally for several months. Then the winter weather moderated. Several weeks later, the fan started coming on automatically when the attic heat built up each day. By 11am, the furnace blower would come on even with the thermostat was set to off. It would remain on until the sun set and the heat dissipated. The only way I could get it to shut off is to go into the attic and shut off the light switch that shuts off power to the full unit.

What causes this and what needs to be done?

Thanks
 
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Old 03-31-11, 04:43 PM
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With attic installed equipment & fans controlled by furnace temperature this is not unusual. If the fan switch is adjustable maybe it could be turned up.
 
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Old 03-31-11, 05:36 PM
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add attic ventilation.................or gable fan
 
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Old 03-31-11, 08:27 PM
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Originally Posted by hvactechfw View Post
add attic ventilation.................or gable fan
Be careful not to pull a vacuum on attic. could interfere with furnace venting.
 
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Old 04-01-11, 04:22 AM
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you would not run a fan in the attic during heating season.............only while it is excessively hot. they typically are thermostat controlled.
 
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