Lennox G43UF cuts out


  #1  
Old 12-15-16, 08:00 AM
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Lennox G43UF cuts out

Son in law has a a Lennox G43UF furnace that keeps going into watch mode. Here's what he has replaced , pressure switch, venter motor which comes with the cut out already mounted, flame sensor
Here's what we have tested , exhaust line and combustion lines both clear, gas pressure after the valve 3.4 "h2o, filter new. Issue is with all covers in place venter motor housing sensor opens and unit goes into watch mode, with the cover off the access area to the valve venter area the unit will run as normal, but the housing of the venter motor is very hot.
We tried to check for a cracked heat exchanger by using match on a long wire inserted into each section of heat exchanger with circulation fan on and flame off. Flame on match didn't waver a bit, I guess its possible that seeing as exhaust is sucked from exchanger that it might not even with a cracked heat exchanger.
Any ideas?
 
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Old 12-15-16, 08:36 AM
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What code are you getting on the red and green LEDS? There are two different codes in WatchGuard.
 
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Old 12-15-16, 11:04 AM
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Lennox cuts out

Green light on, red light flashes slowly.
 
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Old 12-15-16, 02:20 PM
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When the stat calls for heat the first thing that happens is the combustion blower will start. Is that what's happening ?
 
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Old 12-16-16, 06:22 AM
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the fan motor that pulls the exhaust air out of the heat exchanger comes on, then burners on, then circulation fan on
 
 

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