Oil Furnace (Hot Air) Question


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Old 01-06-06, 01:08 PM
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Oil Furnace (Hot Air) Question

I have an oil (hot-air) furnace. Recently I've replaced the old thermostat with a programmable one. I've noticed that the burner will start when the thermostat requires it, however most of the time the burner will cut off before the theromostat is satisfied. A few seconds later it will cut in again until the set temperature is met on the thermostat. My questions are: Shouldn't the burner operate continously until the set temperature is met, and why is it cutting out when the thermostat indicates that it is on and the set temperature is not met. Is this a problem with the thermostat or the burner itself? There doesn't seem to be a problem with the fan. It will continue to operate for a few minutes after the burner stops. The thermostat I have is a UPM programmable.

H
 
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Old 01-06-06, 04:06 PM
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What made/model of t-stat did you get?

On most honyewell, you may need to set the CPH (cycles per hour) to 3.
 
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Old 01-06-06, 05:20 PM
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It is a UPM Programmable Tstat It does not have "cycle adjusting" . All it has is a jumper switch that can be set either for HE or HG. I have it set for HG. The burner will continue to fire if I increase the temperature set point on the Tstat to 2-3 degrees over the room temp. It shuts off when the room temp is 0.5 degrees below the set temp. The blower will continue to run. However, if the room temp does not increase to 0.5 degrees above the set temp within 2 minutes the burner will fire again. Can this be fixed? Or is this just the way this particular Tstat operates?
 

Last edited by H Hewitt; 01-06-06 at 06:15 PM. Reason: additional info
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Old 01-06-06, 07:22 PM
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Originally Posted by H Hewitt
I have an oil (hot-air) furnace. Recently I've replaced the old thermostat with a programmable one. I've noticed that the burner will start when the thermostat requires it, however most of the time the burner will cut off before the theromostat is satisfied. A few seconds later it will cut in again until the set temperature is met on the thermostat. My questions are: Shouldn't the burner operate continously until the set temperature is met, and why is it cutting out when the thermostat indicates that it is on and the set temperature is not met. Is this a problem with the thermostat or the burner itself? There doesn't seem to be a problem with the fan. It will continue to operate for a few minutes after the burner stops. The thermostat I have is a UPM programmable.

H
Sounds like to me its in the burner control circuit itself. possibly a safety
call a repair person unless you can see when the burner turns off and isolate what controller is doing it.
 
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Old 01-06-06, 08:59 PM
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You could try the HE jumper. If it signifies electric, the heat anticipation would be minimal. It seems that your heat anticipation is substantial and that is why the thermostat may be turning off the burner. Anticipating the residual heat in the furnace to bring the room to final temp.

Ken
 
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Old 01-07-06, 05:49 PM
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Thanks for the suggestions! I tried the HE setting and it made no difference. I've been reading up on all of this and it seems to me that this is the normal situation with these types of tstats when controlling an oil hot air furnace. The old honeywell non-programmable tstat that I replaced had a heat anticipator which was set at .2. The furnace would cut in once and that was it. The new programmable unit I have has a "factory set heat anticipation" which cuts out the burner just before the set temp is reached. I have 2 options. Either invest in a more expensive tstat with adjustable heat anticipation, or find ways to make my furnace operate better so that the temp increases faster in the room and the tstat is satisified before the burner fires the scond time.

Thanks
H
 
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Old 01-07-06, 06:19 PM
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You may want to exchange that thermostat for one with more adjustability. I know that the Honeywell 8110 (probably more expensive) can be adjusted 8 ways from Sunday. Cycle rate, overshoot, undershoot, you name it and it can be customized. There are probably others that are not as expensive but the new Honeywell stats are great.

Ken
 
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Old 01-09-06, 07:20 AM
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Smile

My problem appears to be solved! Here's what I did:

1. I Increased the fresh air vent size to the furnace room. I checked this out and apparently my vent was too small by 50" sq. This could have been affecting combustion, since my furnace is in a fairly small confined room.

2. I went around and adjusted every register so that I am getting a more even heat distribution.

3. I also gave the furnace a complete cleaning.

When the oil burner cuts out at 0.5 degrees before set temp there is enough residual heat left in the system to satisfy the tstat, so the burner does not fire the second time, and there is minimum overshoot. Hopefully, this continues. I'm going to check out that Honeywell 8110 though. Sounds like a good tstat.

Thanks,
H
 
 

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