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Mark Henley
Mark Henley, Journeyman Technician
Category: HVAC
Satisfied Customers: 3217
Experience:  UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential
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Troubleshooting Comfort-Aire Conquest 80 furnace.

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I have a Comfort-Aire Conquest 80 Gas Force-air furnace. The model number is  GMUA75-E3N. It is a 75,000 BTU furnace with electric ignition. The furnace has recently had a new air filter put in as well as a new electric ignitor. The problem with the furnace is as follows. The furnace will kick in and the exhaust fan will begin. Shortly after, the electric ignitor will turn on. After this, the burners will light. After about 24 seconds of the burners being lit, the blower will turn on. Sometimes the burners shut right off, sometimes they stay on for a minute. The burners appear to be clean as they are burning with a blue flame. After the burners go out, the exhaust fan shuts off a bit later. Then, the blower goes off awhile after that. When the furnace shuts off, the house is still far from being up to temperature. What should I do?

What type of thermostat do you have?

Customer: replied 7 years ago.
It is a basic round Honeywell mercury filled thermostat. It doesn't have any of the extra buttons that some have for "cool" or "fan only". I had read something before that my heat anticipator setting might be wrong so I tried changing it from .3 to .2 but this didn't do much for me. Another helpful piece of info for you might be that we just bought the house over the summer so I don't know any of the history on how the furnace worked previously.

It is more likely that the thermostat is not level on the wall, if you remove the front part of the thermostat with I believe three small slotted screws it will remove the thermostat and leave the base on the base you will see a line across it, it s a level line, make sure that the line is level or the thermostat will not react at the right temperature, before doing that though can you tell me what will happen if you turn the heat up higher? Will it run longer and drive the temperature higher than what it is right now? By the way the anticipator setting only goes to 1.8 on that thermostat.

Customer: replied 7 years ago.
Thanks for getting back to me. I tried taking off the front part of the thermostat to see if it was level and one of the three screws wasn't all the way screwed in. When we moved in, I was repainting the wall and wanted to move the thermostat higher on the wall. I checked with a level and the thermostat base is level, but like I said, that screw wasn't in all the way. It was one of the screws that also makes a connection with one of the wires to the front part of the thermostat. Also, the heat anticipator is listed as only going to 1.2 on the thermostat but I changed it from 0.3 to 0.2. Do you know what this should be set on? Upon screwing the screw in, I turned the temperature up to 80 (it as 70 in the house from the sun shining in all afternoon) and the burners have stayed on for 10 minutes and are still going strong so that appears that the screw may have been the problem all along.

That's good,

The anticipator setting depends on the type of furnace if this is a newer furnace you can turn it up to 1.2, if it is an old one with a pilot that is lit all the time you can set it lower to around .3, the higher the setting the less it will cycle but more it overshoots and lower the setting the more it will cycle but it may not reach the desired setting, so you got to kind of play it by ear. I just gave you the starting points, usually though .8 to 1.2 is good for most systems.

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