Older ducane oil burner is having short cycling issue and can’t get to the bottom of it
Hi yall - I came across this forum as a last effort into getting my furnace running right again. Seems like there are a ton of extremly knowledgeable fellas in here so I’m posting in hopes to get some advice as I’m at my Witt’s end. Please bear with me as the post is a bit long but I want to accurately describe what has been done so far.
I have an older ducane DRC-15a oil furnace. It’s old but has still been running good surprisingly and I do get annual cleanings. Last year around April we had a tech come out to do the cleaning at the end of the season. At this time we had a service contact. He showed up and replaced a few parts including the pump and blower motor. He went to put it back together and ended up stripping the jet tube fitting where it connects on the nozzle assembly. Said it was “unfixable” and shut the unit down since it was now leaking at the stripped fitting. Said we could get a replacement put in for 15k told him we said we had to think about it - he left.
I consider myself a bit handy - I tried to chase the threads but they were to far gone. Couldn’t source a nozzle assembly since this unit is old. Was able to cut off the bad fitting and add a flare fitting onto it and hook it back up. No more leaks. Fired the unit up - it runs but now is running rough since he never got to finish the tune up. Bit of shaking and banging.
Fast forward to this season - I still have the issue and know I need to get it looked at. I have a new guy come take a look. He goes through the whole unit again. Replaced the filter at the tank , and filter screen on the pump , new cad cell , new nozzle , fixes up some of the old brittle wiring , rebleeds the system and gets a solid stream of oil when he takes the nozzle assembly spins it out and turns unit on and inspects it spraying into a bucket.
He fires up the system - it’s no longer knocking and shaking the house. Seems to run better. After bought 4-5 minutes of it running it now starts to do this thing where it almost sounds like it’s short cycling. It runs and very briefly every 30 seconds or so and then shuts off super quickly and comes right back on. You can see the back pressure make a quick noise at the damper when it fires on and off in the second video below. I show the tech and he explains that he’s basically done what he can and that not to worry I can run it that way and it won’t hurt anything - he packs up and leaves. I’m a bit better off the unit Is not shaking the house anymore but now I have this on and off cycling it’s doing as you hear in the first video linked below.
I decide to take a bit of a look myself again and do some reading. I end up going through all the wiring - re-stripping everything making sure all connections are good since a few people on Facebook mentioned it sounds like a electrical issue cutting in and out. I end up ordering a new primary control for it and throw that in tonight hoping it will finally fix the issue. Unfortunately it didn’t.
That’s where I am as of now - I’ve had two different techs come out. None seem to want to get to the bottom of the issue. Most just want to replace and I can’t blame them I understand it’s old but it was running good before the most recent tune up.
I’ve went ahead and replaced the air filters and even went down to the cheaper version just incase the ones now are to restrictive and causing issue. I disconnected the ecobee thermostat as they can be finicky with older units and jumped it directly at the burner to rule out a faulty thermostat. Still No dice. I’ve made sure all the vents are properly open and clean with no restrictions.
I’m hoping others on here that are more knowledgeable can give me some insight and leads on where to check next. I did notice a different tech from 3 years back was using a 1.00x70b nozzle and the two new techs switched back to a 1.00x 80b nozzle. Could that have anything to do with it?
Another thing i haven’t looked at yet was the transformer and made sure it has a good spark. It’s the original one and very old. Probably the only part that hasn’t been swapped out on this super old burner. I also replaced the Tjurnland power vent about a year ago. I’ve been thinking about just throwing a Beckett AFG burner in it and buy me a few more years until I can replace this unit but don’t want to do so if the exchanger has a crack in it..Hoping that’s not the case 🤦🏻♂️
Only other things I can think of that comes to my mind is like I said a crack in the heat exchanger ( both recent techs said there isn’t one) or the A coil that’s sitting on top of the furnace could be dirty as I’ve read that on a few forums but don’t know if that’s accurate in what can cause this issue and it didn’t start until last cleaning so doesn’t make much sense to me.
I’ll attach the stats of how the burner is running below from the recent tech that was here this week as well as some videos showing what it’s doing. If anybody can give me some more leads to look into it would be very helpful as we have no heat right now besides propane back up fire place and I’m in the process of putting a new mini split in. Would really like to get another year or two out of this furnace before we replace it. It was running perfectly fine before the first tech came to do a tune up so makes me think it’s something that is fixable. This all didn’t happen until the last tune up.
This years techs readings -
616.8 - StackTemp
66.0 - Temp c
7.5% - 02
4ppm - CO
1.55 - Lambda
10.09% - Co2
6ppm - Co
17.5 - QS
82.5 - Efficiency
Techs readings from two years ago -
582 - Stack temp
-60 - Net stack temp
10.9% - Co2
0% - Smoke
.05 - Breach draft
.03 - Over fire draft
79.5 - Efficiency
Techs from three years ago -
6.7% - o2
2ppm - C0
10.7% - c02
Eff total - 84.1
Loss total - 15.9%
T flue - 430.7
T air - 64.0
🔺T - 366.7%
Exc air - 47%
C0 ref - 3ppm
Draft - -0.060
Pgas - -0.036
Two videos attatched of how it’s running currently…recent tech said it’s safe to run like this. Is that true?
Comments
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Videos didn't upload.
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The large nozzle that was installed may be causing it to cycle on high limit because it’s over-firing.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.0 -
Stop chasing electrical problems. Once an oil burner is firing and stable, it will keep right on going, spark or no spark, so long as it gets oil and too much air doesn't literally blow the flame out. My first cut thought is that there is a problem with the oil supply… but I'm not a burner guy.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Looking at the video, I see what may be a flame sensor problem. The primary control is seeing the flame via the cad cell, then it is not seeing the flame and drops out then immediately restarts. try this temporary test. after the flame is established and before it drops out place a jumper wire from F to F and see if the dropping out stops.
this is a common problem with the R8184M primary control. It is unfortunate that you purchased that same control because there is a better one for you.The Carlin 70200 ProMax will include diagnostics but you will also need a Beckett 51950U AC kit to make up the air conditioning portion of the system.EDIT: New info update. this is connected to a power vent and that is the cause of the short cycling
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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I agree with @Ironman they could have installed a larger nozzle and your cycling on the high limit. Check to see if the high limit is opening. If it is you need to increase the air flow of the indoor blower or more likely install a smaller nozzle.
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How's the pump pressure? Was it increased to 140 psi and now the nozzle is oversized?
Anyone check the pump diaphragm for pinhole?
Has the pump to motor coupling been checked for wear that could cause slippage?
Is the end cone bent/cracked?
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Wow, I'm seeing this posted everywhere. Here, HVAC Talk, Reddit.
Maybe you should try harder to find a better tech. To diagnose these problems you really need to be on site with all the right tools. Combustion analyzer, pump pressure testing manifold, multimeter and much more.
Whoever did that combustion analysis set it up too much on the lean side. 7.5% O2 is too high. Should be able to get a true zero smoke at 4.5-6.5% O2,0somewhere in the range of 450-550⁰ with the over fire draft measuring -.01"-.02" and the breach draft -.03"-.04". That stack temperature is a bit high at 614⁰.
What primary control are you using? Does the furnace have a fan center control or just a fan and limit control? Pictures of everything would help.
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Appreciate the comment - I double checked the cad cell today with multimeter and that is ok. It was changed right at the end of the last season as well and got very little use if any. I’m still trying to get to the bottom of this and super frustrating
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I’ve been chasing it from every direction possible and still haven’t got to the bottom of it. I have many people say it’s electrical issue so that’s what led me that way. People saying it’s a voltage drop issue. I’ve checked pump pressure as well as installed a new pump and I’m getting a good supply of oil
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They work when I click them and a few others have accesed them. Can you still not get them to work? If not I can try and send another way. Thanks
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Did you try my temporary jumper trick? After you get the oil burner operating, place a jumper to connect F to the other F. Don't depend on the Cad cell to do that for you. If the burner stops the cycling and you knoe that the Cad Cell is working, then the brand new control os bad.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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hi there yes I tried jumping out the car cell and the cad cell Is working normally. Thanks for the tip. Today I ran out and grabbed a better multi meter that actually has a clamp on it to test for amps and voltage drop. I fired up the unit it ran for about 5 min and I had my clamp on the motor and was montering it. Sure enough voltage is dropping super quick momentarily to almost 0 and then going right back up. I went over to the power vent as I replaced the power vent blower wheel and motor last year. It’s Tjurnland brand. But did not replace the control board. When the voltage drops momenerily you hear a click right at the power vents electric board at the same time. I think I’m getting somewhere a bit closer..here’s a video of the voltage drop.
https://streamable.com/4du4sa
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Yes I have checked all things named in your comment so far thank you for the help. Today I ran out and grabbed a better multi meter that actually has a clamp on it to test for amps and voltage drop. I fired up the unit it ran for about 5 min and I had my clamp on the motor and was montering it. Sure enough voltage is dropping super quick momentarily to almost 0 and then going right back up. I went over to the power vent as I replaced the power vent blower wheel and motor last year. It’s Tjurnland brand. But did not replace the control board. When the voltage drops momenerily you hear a click right at the power vents electric board at the same time. I think I’m getting somewhere a bit closer..here’s a video of the voltage drop.
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That explains a lot
When installing the Tjernlund I remember that the wiring diagram calls for the power vent control to be powered from the orange wire on the primary control (motor) and that will operate the power vent motor. Once the power vent fan proves the fan is operating, there is a switch in the power vent control that completes the circuit to the burner motor.
Your power vent control proving switch is dropping out from the pressure difference of the oil burner combustion. That cuts the power to the burner motor. Once the flame goes out the power vent prover switch will re-engage and power up the burner motor. Since the primary control has no way to tell what is going on, and the safety timing on your primary is 45 seconds, the primary will stay on for the duration of the call for heat
See if there is an adjustment on the Tjernlund proving switch so it does not drop out once the oil burner ignites.
Does the vent between the power furnace and the power vent have a barometric draft damper? Is it properly adjusted?
I'm not sure what power vent you have but if you are using the HSJ, HS1, or HS2 this is where the adjustment might be.
Try adjusting this lever/damper when the burner is short cycling. Lock the adjustment when the short cycling stops.
Then you will need to get a combustion analysis to make sure you didn't create another problem with that adjustment. You don't want to get soot all over your home.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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this is great info! Thanks for taking the time to explain. The power vent is a Tjurnland hs1. I replaced the blower wheel and motor on the vent last year but not the electrical board. Today I dug into it a bit more. As I stated before I’m seeing a voltage drop at the motor on the front of the burner.
I removed the cover on the power vent board and put my multimeter on the incoming voltage wires and I’m getting a constant 116 volts and when the unit cuts on and off I’m not experiencing the same voltage drop at the power vents board as I am at the motor on the front of the furnace. I pulled the power vent apart and checked for obstructions as well as the small tube on the proving switch / pressure switch to make sure it was clean and not clogged.
From there I removed the pressure switch on the power vent and hooked my multimeter to it and ohmed it out while sucking on the tube to recreate the pressure needed as if it was operating. When doing so the proving switch / pressure switch passed the continuity test and seems to be working properly. You can hear it also open and close.
On the power vents board when the flame goes in and out you can hear a distinct clicking noise that is coming from the board and sounds like one of the relays clicking on and off at the same time the flame goes in and out for that quick half a second. I also noticed there is a series of lights that are suppose to be on when going by the diagram for the hs1 and one of them is missing as well as when the unit cuts on and off there is another light that alternates and blinks at the same time. I’ve attatched a few videos to give you a better idea of what’s going on when the furnace is operating and shows you what the power vents board is doing. Thanks again for the help.
https://streamable.com/l9fpoihttps://streamable.com/8p5pb7
https://streamable.com/5vqkej
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i can see from the video that you are testing the voltage on the 120 VAC power to the Tjurndlund control. It appears that you are testing only the power to L and N (Green oval) on that control. That will always have power by design. You will want to check the voltage across terminal 2 and 4 (Red oval). that is where you will see the voltage to the burner motor drop out. I can see it happening on the LED display of the Tjurndlund board.
And here is what is happening
- The pressure switch that you tested is making a set of electrical contacts when ever the Tjurndlund fan operates. You proved that with your continuity test. So that is working.
- The burner motor is powered thru the Tjurndlund control terminal 4 once the pressure switch is closed
- The combustion process in the flame will increase the over fire pressure in the combustion chamber do to the rapid expansion of gasses from the combustion process.
- That pressure will travel thru the heat exchanger, the vent connector and to the Tjurndlund fan in about 2 to 10 seconds…. That pressure change will affect the pressure that the pressure switch is measuring.
- Within a few seconds from that, the switch will open
- That will signal the Tjurndlund control to stop sending power to the burner motor
- Once the flame goes out and the pressure is equalized in the vent system the pressure switch will close the pressure switch contacts and the burner motor will start and the flame will light.
- And the process starts all over
In order to make that short cycling stop. you need to make sure there is sufficient pressure to the pressure switch during the entire call for heat. that adjustment is done at the lever on the side of the Fan unit, I indicated in my previous post.
Hope this helps.
If you cant fix the problem with the adjustment above, then you may need a new pressure switch that is less sensitive to the pressure changes in the vent system.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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I saw this same query on a Facebook group called "Oil Tech Talk" today. I guess you didn't like my answer Justin. But it is the Tjurndlund pressure switch that is opening and causing that burner motor to stop and restart.
Ask me how I know?
I made some minor edits to my last post on the steps to correct the problem.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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