Rheem oil furnace burner turns on sparatically

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Old 10-20-10, 01:14 PM
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Rheem oil furnace burner turns on sparatically

Wondering if anyone can help me out on this. I have a Rheem oil furnace model ROBC-067LBEA controlled by a Honeywell programmable thermostat. The furnace runs fine and goes through its normal cycle when the thermostat is calling for heat. The problem is when there is no call for heat, the burner will still start on its own and run for about a minute and then shut off, and the blower does not run at all. The burner will go through this about every 15 minutes, and when the thermostat does call for heat, then the blower will start and it will operate like normal. The only way I can stop this from happening is turning off the power switch on the side of the furnace. If I shut the furnace off by using the switch on the thermostat, the burner will still go through this cycle. I also have central air but have had no problems with it. My question is, does this sound like the thermostat has gone bad or would it be inside the furnace. I was assuming that the thermostat is what controls what the furnace does, but figured I would ask before spending $50 on a new thermostat if the problem might be bigger than that. Thanks for any type of help!!

The oil burner is a Beckett model "AFG"
I also just tried taking the thermostat off the wall and took off two wires while it was running and it didn't change anything, the burner ran for about a minute anyways.
 
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Old 10-20-10, 02:09 PM
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I'd bet that the burner is being turned on by the thermostat or thermostat wires.

Check to see if you have 24 VAC on both thermostat wires when the burner is operating erratically as you describe.

At least that would be a good place to start.
 
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Old 10-20-10, 02:26 PM
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A little more info, I just took the thermostat off completely and disconnected all 4 wires and the burner still comes on and does the same thing, just runs for about a minute.
 
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Old 10-20-10, 02:39 PM
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That's a start. I'd check the voltage on the thermostat wires to the burner, or disconnect them.

Thermostat wires can get cut on sheet metal or otherwise short together, causing equipment to run when it shouldn't.
 
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Old 10-20-10, 02:58 PM
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I disconnected the thermostat wire inside the furnace, but it didn't help. The burner just kicked on again
 
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Old 10-20-10, 05:51 PM
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Tried a couple more things....

Originally Posted by Jeffr74937 View Post
I disconnected the thermostat wire inside the furnace, but it didn't help. The burner just kicked on again
I tried some more things. After ruling out the thermostat and the thermostat wire, I traced all of the wiring in the furnace to make sure there are no shorts. I also noticed that when I turned the AC on, the burner would kick in even with that. My theory is that something had to be stuck on, like a relay. When the burner would turn on it would run for a minute because it took about that long for the limit switch to turn it off, and it would take about 15 minutes for the furnace to cool down enough to let the burner turn on again, but a relay somewhere is stuck in the on position. Im guessing the reason the blower doesn't go on is because nothing is calling for heat in the first place. I traced the wiring diagrams, and Im thinking it may be either a isolation relay, or a heat/cool relay.
Anybody have any idea with this? Or am I just driving myself crazy!!

Thanks
 
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Old 10-20-10, 08:22 PM
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Rheem

Rheems are known for trouble with those relays. Replace them both. Sure as the sun will rise tomorrow if you replace one the other will soon crap out.

BTW: If your thermostat is powered by the furnace, replace it with a battery powered one. I don't mean one with battery backup but truely powered by batteries. Furnace powered thermostats & oil burners are a bad mix.
 
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