Older ducane oil burner is having short cycling issue and can’t get to the bottom of it

Boston0991

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?

https://streamable.com/tjzz7x

https://streamable.com/c32ksm

HVACNUT

Videos didn't upload.

Ironman

The large nozzle that was installed may be causing it to cycle on high limit because it’s over-firing.

Jamie Hall

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.

EdTheHeaterMan

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.

Here is the video

https://streamable.com/tjzz7x

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.  

 

EBEBRATT-Ed

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.

Patchogue Phil_2

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?

SuperTech

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.