Furnace malfunction


Old 12-07-02, 07:56 AM
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Furnace malfunction

My furnace has begun to cycle. As soon as the fan kicks in, the flame goes out. The fan runs for a while, then all stop. After 5-10
min. the flame comes on full, and after a couple of min. the fan comes on, and the flame goes out again. HELP. Is it possible this is a fan limit switch, or hi temp limit switch failure? This unit is a Lennox GS6-130, 1960 vintage, but well maintained, gas fired.
My owners manual, and installation manual have suffered the ravages of time, and are un readable. I need to locate the code lights, where should I look?

Last edited by fluff42; 12-07-02 at 08:51 AM.
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Old 12-07-02, 11:03 AM
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It's possible that the fan/limit switch is either bad or way out of adjustment.

The fan may not start until the bonnet is near the limit setting.

If you are comfortable inside the furnace and have a basic electrical knowlege you could check it.

A good place to start would be fan on at 160 deg F and off at 120 deg F.
Old 12-08-02, 05:20 AM
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Your model lennox does not have LED diagnostic. Also lennox used a positive 'on' type fan/limit switch which did not depend on heat from heat exchanger to turn on fan. They had an extra heater coil installed in their fan limits to turn fan on after 90 to 120 seconds, no matter what heat exchanger temp was.

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