Original message
| MikeJiang
 |  "High Limit Problem ?"
, posted Sat 26 Jan 17:13  
Lennox Model 80MFG 3/4 will not obey thermostat. Stops operation at 10 degrees below setting and will have both diagnostic LEDs flashing simultaneously when working and the high limit code when it stops in most instances and sometimes the vacuumm switch. I am confused . How can I be certain the thermostat is working correctly and when is the high limit correctly shotting off the gas and how can I tell if this is a malfunction ?
SOS
PS... How do I fix ?
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Replies:
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| amech
| "Re(1):High Limit Problem ?" , posted Sat 26 Jan 17:17
If your high limit is shutting down the furnace. You potenially have a serious problem. Need to call for service. Makeno mistake, it is a malfunction and that not normal.
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| | marchvac
| "Re(2):High Limit Problem ?" , posted Sat 26 Jan 19:21
What is the full model# and serial#. Has the furnace ever been serviced? What is the size of the filter and is it clean? Are all of the floor registers fully open? Have you ever had the filter left out of the furnace for any period of time? There is four or five speeds for the fan which one is on the heating tap. Is the chimney clear? These are all things that we need, to try and diagnose these problems and while your doing these you might want to clean the flame sensor.
Be careful sometimes you don't get a second chance
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