# Oil Furnace Short Cycling, Honeywell R7284 Control



## JRP3 (Dec 2, 2017)

I noticed that the furnace at my parent's house is shorty cycling, specifically the burner kicks on, fires for 2 minutes, shuts off for 1 minute, then that cycle repeats continuously until the set temperature is reached and the thermostat turns it off.  The blower keeps running as the burner cycles on and off since the heat exchanger stays warm for the 1 minute off cycle.  The Honeywell R7284 controller only shows an old error about 2700 cycles ago, probably when installed, which was a few months ago, in April I think.  The display shows about 200 Ohms while the burner is running, which seems about right.  Any ideas?


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## brenndatomu (Dec 2, 2017)

Tstat bad? Transformer cutting out?


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## Hogwildz (Dec 2, 2017)

Has the filter been changed? Might be starving for oil.


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## JRP3 (Dec 2, 2017)

T-stat is pretty new, a few months old, don't know about the filter or transformer, but I think it was all serviced around the same time, if not at the same time, as the new burner control and T-stat install.  The fact that the cycling seems exactly the same time period each time, 2 min on 1 min off, makes me think it's a programming or timeout problem with the burner control.  Or maybe the burner control is getting a signal that the heat exchanger is over heating, so it shuts down for a minute?  I assume there is some sort of limit switch to prevent the heat exchanger from over heating?


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## brenndatomu (Dec 2, 2017)

I wonder if the Tstat was programmed right, assuming it is a programmable one...needs to be set for a oil furnace...


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## JRP3 (Dec 2, 2017)

Doesn't the T-stat just put out a signal for the furnace to turn on, and then turn off once the temp is met?  Does the T-stat get a signal back from the furnace?


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## brenndatomu (Dec 2, 2017)

Yes, just calls for heat. (or AC)
No feedback signal...that I've ever seen, but, Tstat needs to be programmed to the correct type of heat for the proper anticipator setup, also cycles per hour...


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## JRP3 (Dec 4, 2017)

I looked up the manual for the T-stat, I think it's a Pro 900 series, and the manual shows a setting for Fan Set, either GAS or ELEC, and it's on GAS, even though it's an oil furnace, but there is no other choice.    It says "Select GAS for systems that control the fan during a call for heat.  Select ELEC to have the thermostat control the fan during a call for heat."
The Heat Swing or anticipation is set for 0.4, which seems normal.  So I don't think the problems is T-stat related.  Also when watching the burner control it never goes into "Standby" until the proper temp is finally reached as determined by the T-stat.


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## brenndatomu (Dec 4, 2017)

Hmm, sounds like this may need more than an internet diagnosis...


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## JRP3 (Dec 4, 2017)

Yeah, I think maybe the burner control unit is faulty or was improperly programmed when it was installed, and I just happened to notice the behavior because I was staying at the house and my room was right above the furnace room.  My parents never would have noticed as long as it was producing heat, or cold in the summer.


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## johneh (Dec 4, 2017)

Just talked to my son he is HVAC teck He said in his limited experience with oil 
that is is moat likely the Heat Anticipation control at the stat 
Or the Cycling unlimited control at the furnace . As I have no idea about furnaces 
I am just adding to the pot 
He also said in ether case get a lic tek to do the diagnoses as he has 
the tools and the knowledge   I no just hate to spend the bucks


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## JRP3 (Dec 4, 2017)

Appreciate the info.  If it were in my house I'd keep messing with it until I figure it out, but don't want to chance stranding my parents without heat, so I'll probably call the pros.


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## begreen (Dec 4, 2017)

What happens if the thermostat is set to a much higher temp, temporarily to test? If you set it to 80F, does the furnace run continually or still short cycle? If it runs continuously, the issue is most likely at the thermostat and the swing cycle setting needs to be higher. If the short cycling persists in spite of the high thermostat setting then the issue is most likely at the furnace. 

Question: Is the thermostat in a location away from any drafts or supply vents?


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## JRP3 (Dec 4, 2017)

T-stat is away from any vents or drafts.  Haven't tried setting it high.  I'll give it a shot.


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## Hogwildz (Dec 4, 2017)

If the overheat limiter is fried, it will also cause this issue. I had to replace mine a couple years ago. Just went, no warning. But should also trigger the safety and stop it from running at all.


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## Sodbuster (Dec 4, 2017)

1 Anticipator setting T-Stat, set it to a higher lever.
2 Fuel filter, if not sure of replacement, replace it, to eliminate that cause.
3. Eliminate overheat limiter, by forcing a 5 degree rise.


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## JRP3 (Dec 7, 2017)

Tried increasing the swing time from .4 to .8, no difference, tried setting the T-stat to 80F, no difference.  I did notice that the run time for the burner varies, anywhere from around 2 minutes to 6 minutes.  I also noticed that as the burner shuts off a different message flashes on the screen for a split second, too fast to read it, so I used my phone to record a video and then paused it at the point the message comes up.  It says "Burner Off Delay 02:00".


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## blades (Dec 7, 2017)

smart move on capturing that flashed message. it sure sounds like limit sensor problem,  you had any good electrical storms since the install?


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## Sodbuster (Dec 7, 2017)

Does sound like a limit sensor, sometimes those can get gummed up, try removing it, and shine it with some fine steel wood, see if that helps. If not, try a new one. You should be able to check it with a multi meter.


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## trailrated (Dec 7, 2017)

I had this issue some years back. Burner was reaching its high limit temp. Should be a gauge inside the furnace near the oil motor and pump. My furnace was starving for air, needed more return air. That and annual tune ups from a good tech solved the issue.


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## jatoxico (Dec 7, 2017)

This is probably a dumb question but is the high/low switch set too close together or too low settings? Typical winter setting is about L=160, H=180. If setting is too close or L is too low the returning water is warm enough that it's satisfied too soon or H not high enough so water in boiler comes to temp too early.


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## JRP3 (Dec 7, 2017)

It's a forced air oil furnace not a boiler.


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## fbelec (Dec 8, 2017)

simple go there and jump out at the burner T T or where the tstat is hookup if it still does it the thermostat is not the problem. look at the temp of the air coming out of a vent is it warm or hot? is the blower running all the time the call for heat is there? it should be. if not replace the fan center. if you don't have one take a picture of the inside of the furnace so we can tell you what to check.


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## JRP3 (Dec 8, 2017)

fbelec said:


> simple go there and jump out at the burner T T or where the tstat is hookup if it still does it the thermostat is not the problem.



You mean to disconnect the T-stat connection and put a jumper across the terminals?



> is the blower running all the time the call for heat is there? it should be.



Yes, fan keeps running as the burner cycles on and off.


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## Sodbuster (Dec 8, 2017)

JRP3 said:


> You mean to disconnect the T-stat connection and put a jumper across the terminals?
> 
> 
> 
> Yes, fan keeps running as the burner cycles on and off.



Does this furnace have a dip switch for emergency heat, (everything high mode) if so try that, if it doesn't do it then looks like overtemp sensor to me.


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## fbelec (Dec 9, 2017)

JRP3 said:


> You mean to disconnect the T-stat connection and put a jumper across the terminals?


yes

does you furnace have this control
if so take off the cover and watch it se if it moves right. watch it from cold. pull it out and look at it see if there is and buildup on it.

https://www.homedepot.com/p/Honeywe...gclsrc=aw.ds&dclid=CIiSvfed_NcCFQSnyAodxkoEZg


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## JRP3 (Dec 9, 2017)

fbelec said:


> yes
> 
> does you furnace have this control


No, doesn't have that.  The furnace is this unit https://www.lennoxpros.com/of23q34-105120-furn-oil120kb3-4ton/p/26K75
This is what it looks like in the burner area


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## begreen (Dec 9, 2017)

Unfortunately Lennox does not make it's manuals and schematics easily available.
Is the blower coming on a little bit after the furnace comes on?
Has the filter been checked?
Has the burner photocell been checked to see if it is dirty?
Is there a low fire pressure switch in the system and if yes, has it been checked?


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## Hogwildz (Dec 9, 2017)

If it is cutting off before the blower fan kicks on, I'd bet it is the high temp limiter.


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## JRP3 (Dec 9, 2017)

When the furnace first fires up the burner runs, then the fan comes on, and the fan stays running as the burner cycles on and off, until temperature is reached.  The cad cell readout hovers around 200 ohms when running, which is the normal range from what I can tell.  
By filter do you mean the air filter or oil filter?   I looked at the air filter today and it seems to be clean.  I don't know about a low fire pressure switch.
I did take the cover off that covers the circuit board and noticed some slight burning on the board near a ceramic resistor.  I think after the weekend I'm just going to call the pros and let them deal with it.


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