Gas and Oil Home Heating Furnaces - Old Bryant Gas unit cycling in auto
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atlbrent
11-07-07, 06:16 PM
Let me start by saying boards like this are incredible sources of info and help...part of the reason I got online way back when.
So here is my question/issue/situation:
In Atlanta, GA where winters can be all over the map. In a 1974, 2 story brick with large unfinished walk up attic. Currently have a ~20yo Bryant Natural Gas 140k BTU unit in the attic for the whole house heating. Unit pulls air from the side and sends it out going upward through the exchanger. No zoing or auto-dampering. Honeywell CT2800 thermostat (1997) that is mounted downstairs in hall.
The problem is this:
The Unit goes into a cycle of some kind where the vent fan kicks on, 60 seconds later the burner fires up. 60 seconds later, the Fan kicks on at the same time the burner kicks off. Then finally, the fan kicks off and the whole loop starts again.
It gets into this loop when in auto modes like hold temp, full auto, or any other auto mode. The loop it gets in never gets heat going and the house will cool down as far as it can go. Right now, we run with the fan in the ON position and not AUTO which allows for the temp to go up fully according to the settings. However, even in fan ON mode, the fan will be running and then stop, the burners fire up, and then the fans will kick on shortly after.
Here is what I have done so far...
-New clean filter to ensure air flow is good.
-Some board was replaced by local HVAC company in town when home was purchased. Did not fix anything.
-One very knowledgable came out and said he wanted to replace the limiter in the airflow chamber since when he put his thermometer in to the airflow, it was reading hot in the 190 degree range. If this limiter was increased, would that not increase the risk of the unit over heating? we elected not to do it and suffer through the fan ON through last winter.
- In Atlanta, we are finally getting the cold stuff this week and the heat is back on. We have an American Home Sheild home warranty that came with the home. I know, they suck. anyways, they sent someone out today that seemed to not want to touch anything. He said it was probably the thermostat.
I know this is a ton and after a long day of fighting the bad guys at work and dealing with this, I may have left out some key details. I have checked other posts on the board and can't find anything where someone has solved a problem like this.
Can you folks look at these details and ask any questions you may have? I am trying to find out if this is one of the below:
.Thermostat
.Electrical on Furnace (board, exhaust fan controls, some other thing.
.the heating unit or core itself
.airflow related
.gremlins
I will most likely drop the home warranty since it was a waste of $55 to have them even come out.
Thanks everyone!
So here is my question/issue/situation:
In Atlanta, GA where winters can be all over the map. In a 1974, 2 story brick with large unfinished walk up attic. Currently have a ~20yo Bryant Natural Gas 140k BTU unit in the attic for the whole house heating. Unit pulls air from the side and sends it out going upward through the exchanger. No zoing or auto-dampering. Honeywell CT2800 thermostat (1997) that is mounted downstairs in hall.
The problem is this:
The Unit goes into a cycle of some kind where the vent fan kicks on, 60 seconds later the burner fires up. 60 seconds later, the Fan kicks on at the same time the burner kicks off. Then finally, the fan kicks off and the whole loop starts again.
It gets into this loop when in auto modes like hold temp, full auto, or any other auto mode. The loop it gets in never gets heat going and the house will cool down as far as it can go. Right now, we run with the fan in the ON position and not AUTO which allows for the temp to go up fully according to the settings. However, even in fan ON mode, the fan will be running and then stop, the burners fire up, and then the fans will kick on shortly after.
Here is what I have done so far...
-New clean filter to ensure air flow is good.
-Some board was replaced by local HVAC company in town when home was purchased. Did not fix anything.
-One very knowledgable came out and said he wanted to replace the limiter in the airflow chamber since when he put his thermometer in to the airflow, it was reading hot in the 190 degree range. If this limiter was increased, would that not increase the risk of the unit over heating? we elected not to do it and suffer through the fan ON through last winter.
- In Atlanta, we are finally getting the cold stuff this week and the heat is back on. We have an American Home Sheild home warranty that came with the home. I know, they suck. anyways, they sent someone out today that seemed to not want to touch anything. He said it was probably the thermostat.
I know this is a ton and after a long day of fighting the bad guys at work and dealing with this, I may have left out some key details. I have checked other posts on the board and can't find anything where someone has solved a problem like this.
Can you folks look at these details and ask any questions you may have? I am trying to find out if this is one of the below:
.Thermostat
.Electrical on Furnace (board, exhaust fan controls, some other thing.
.the heating unit or core itself
.airflow related
.gremlins
I will most likely drop the home warranty since it was a waste of $55 to have them even come out.
Thanks everyone!
chitown630
11-07-07, 09:27 PM
Unit is pulling 100% outside air? Not from GA so not sure if that is how they do it there.
Do not change high limit like tech said, just will allow unit to run alittle longer till limit opens up at higher temp, only will increase chance of damage to unit or fire, will cause strain heat exchanger, causing shorter life span.
How large is the house, square foot approx? Unit possibly oversized? Is thermostat sensing direct airflow from vent in house?
More info plz.
Do not change high limit like tech said, just will allow unit to run alittle longer till limit opens up at higher temp, only will increase chance of damage to unit or fire, will cause strain heat exchanger, causing shorter life span.
How large is the house, square foot approx? Unit possibly oversized? Is thermostat sensing direct airflow from vent in house?
More info plz.
ecman51`
11-08-07, 08:13 AM
However, even in fan ON mode, the fan will be running and then stop, the burners fire up, and then the fans will kick on shortly after.
This is something quite key in your entire post, I'd say.
So the blower fan, when set on the stat to the "on" mode, will behave the way you say in your quote snippet above, when starting out with even a cold furnace, before the burners ever come on?
And the board was replaced?
I am presuming your numbered Honeywell is a (programable) digital? Anyone try jumpering wires or trying out another thermostat?
This is something quite key in your entire post, I'd say.
So the blower fan, when set on the stat to the "on" mode, will behave the way you say in your quote snippet above, when starting out with even a cold furnace, before the burners ever come on?
And the board was replaced?
I am presuming your numbered Honeywell is a (programable) digital? Anyone try jumpering wires or trying out another thermostat?
daddyjohn
11-08-07, 05:18 PM
Hi Brent:
If the temp reading at the limit control is 190F, that is the problem. Things to check: is the blower running? You sure? Is the blower running in the right direction of rotation? [the concave surfaces on the blower wheel pick up the air] Is the blower wheel intact? Look at both sides, IOW- pull out the blower housing. Is the return air blocked? Check the cooling coil to see how dirty it is. Sometbing is restricting/diminishing the airflow and cauing the furnace to run hot. Let us know what you find.
If the temp reading at the limit control is 190F, that is the problem. Things to check: is the blower running? You sure? Is the blower running in the right direction of rotation? [the concave surfaces on the blower wheel pick up the air] Is the blower wheel intact? Look at both sides, IOW- pull out the blower housing. Is the return air blocked? Check the cooling coil to see how dirty it is. Sometbing is restricting/diminishing the airflow and cauing the furnace to run hot. Let us know what you find.