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Help needed- strange problem

We need assistance from anyone was has seen or knows about this problem we are have with an oil burner.
Carlin 201 CRD
The problem we are having is we are going through cad cells almost every 10-14 days.
They appear to be shorting out.
On either of the newer digital primary controls (7284 or ProMaxx) either control keeps coming up with the error “flame detected”. Ohms our the eye on a dark background, 600 ohms plus.
We have gone through over 10 cad cells and leads by now.
So here’s what we’ve done so far:
All controls have been replaced.
New L7284, 2 each new primary controls- 7284u’s and Carlin 70200 Pro Maxx’s. New delay oil valve. New igniters.

The TT or end switch connects to the L7284 not the primary control.

When the cad cells “go bad” they are not cloudy, melted or anything.

Also, all of the wiring from the service switch on has been replaced with new wiring.

We’ve checked for everything.
We’ve replaced everything.
More than once.
No matter what we do, same result.
The cad cell keeps going bad.
Also, we have no back pressure, no stray light.
We have 7 seasoned technicians, most of us doing this for over 20 years.
We are at our wits end.

Anyone have any ideas??


  • Jamie Hall
    Jamie Hall Member Posts: 23,436
    I probably shouldn't sy anything -- since I know next to nothing about oil burners.

    But -- fools rush in where angels fear to tread. Is there any possibility that something amiss in the vicinity of the cad cell is allowing direct flame impingement on it?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • northernboiler
    northernboiler Member Posts: 55
    The cad cell isn’t picking up stray light.
    It’s shorting out. Preventing the burner to fire.
  • Ironman
    Ironman Member Posts: 7,379
    Has anyone checked the incoming line voltage? Has anything else in the house blown or burned out unexpectedly?

    You could have a loose neutral connection on your electric service which will cause voltage spikes.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • northernboiler
    northernboiler Member Posts: 55
    We have checked everything. I can’t tell you how many times.
    Redone everything.
    No stray voltage. Everything runs perfect.
    Then out of nowhere, the cad cell goes bad.
    Nothing else malfunctions. Or is defective.
    Just the cad cells. Over & over.
  • DZoro
    DZoro Member Posts: 1,048
    Can you post some pictures of your set up?
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited October 2019
    I'd guess it's heat related, or a grounding issue.
    I've never heard of a cad cell 'shorting out'. It's flame detection converted into ohms. Usually heat kills them.
    I'm not quite sure how you are determining the cad cell is bad.
    I also guess changing all the part even though they didn't test bad out of desperation has you more confused.

    Do you have a meter with a k type thermocouple? Slip that in the air tube, watch the temperature while the burner is running, and for a few minutes after shutdown. If the heat is excessive, that could be your problem. Then you either have a dirty boiler, plugged chimney, bad venting, or need extended post purge.

    No light-cad cell should read infinity.
    Burner running, 600-1200 ohm range, maybe even higher.
    You can read running ohms off of either of those primary controls.

    'We checked everything' Technically you haven't or you would've found the issue ;)
    So I assume you're one of the techs.
    -When you get to the burner, what does the control say happened?
    -When you reset it, does it run? If so, what ohms reading on light off, and does it stabilize.
    -If it doesn't run, does it fail to light, or light, but lockout?
    --What are your complete combustion numbers, including draft?
    -Make/model number of what this burner is attached.
    -Nozzle, pump pressure?
    -Gravity or lift, 1 pipe or 2 pipe, and any Tiger Loop.
    -Venting-chimney or power vented.

    A picture of the whole set up showing the flue pipe into the chimney base could help too.

    Side note...Last year I did get a whole strip of cad cell eye's, the ones the supply house has on a strip like candy. They were all bad. I just stick with the Honeywell's.

    Edit: Also, where are you located?

    There was an error rendering this rich post.

  • northernboiler
    northernboiler Member Posts: 55
    Can’t post any pics.
    Let me put it this way.
    This boiler & burner is wired and installed just like almost every residential oil boiler.
    Absolutely nothing special or unusual.
    We simplified it because we can’t figure out why we keep having the cad cells go bad.
    Every wire, control, part is new. More than once.
    The cad cells just keep going bad.
    About every 10-14 days.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    Have you checked the transformer supplying current to the cad cel? Maybe some 110 v. stray currents are frying the cel.--NBC
    rick in Alaska
  • ScottSecor
    ScottSecor Member Posts: 863
    I'm with @STEVEusaPA . I haven't tested a cad cell in about twenty years but the resistance is what I would check out first. Check it while running, immediately after a cycle and just before burner turns on. I bet you'll find the problem.
    Alan Welch
    HVACNUT Member Posts: 5,863
    edited October 2019
    Is the firing rate correct for the 201 and the boiler? Nozzle, angle, spray pattern.
    What does the combustion report say?
  • rick in Alaska
    rick in Alaska Member Posts: 1,457

    Have you checked the transformer supplying current to the cad cel? Maybe some 110 v. stray currents are frying the cel.--NBC

    Since it isn't melted, I would agree about checking the voltage going to it. Since it is shorting out, voltage is killing it somehow. I don't know how you will find it though, especially since you have changed out the controls that power it. It would seem if it was a power spike, it would also kill the control.
    Good luck.
  • Mike_Sheppard
    Mike_Sheppard Member Posts: 696
    I had a similar situation, but it was on a large commercial boiler. The boiler and burner had only been running for about a month. But the UV scanner kept going bad. I went there twice, two different Saturdays, to find the UV scanner bad. I replaced it. Checked it out. Worked fine. Next weekend it was bad again. New installation.

    Turns out during the week they ran a large exhaust fan connected to the room which was pulling the room into a negative pressure. When the boiler turned off it would begin backdrafting and the heat was killing the UV scanner. I would check for backdraft. Let the boiler run then stick a thermocouple inside by the cad cel and see if it heats up.

    Also, everyone here is trying to help you. Obviously there is something wrong that you and your co-workers haven’t found yet. Things like pictures, combustion numbers, temperatures, draft readings, etc are what we are going to need to help you solve this.

    What’s your O2%?

    What are your draft readings during standby and firing?

    What’s the stack temp?

    What’s the room pressure during standby and firing?

    If there are voltage spikes you probably aren’t going to be there when it happens. If nothing else works out you could put a logger on the electrical service to rule that out.
    Never stop learning.
  • ScottSecor
    ScottSecor Member Posts: 863
    @Mike_Sheppard brings up a good point that I have also witnessed. When I first started in the heating business we picked up an account that had a fire in a almost brand new building's boiler room. The high rise building was used as public housing for senior citizens. There were six Hydrotherm oil fired boilers ("Multi-Pak"), two boilers were mostly used for DHW and the remaining four were used for heat.

    One night the staff decided to leave the boiler room exhaust fan on because it was rather warm in the boiler room. Around midnight we got a call from the fire department that we needed to get there immediately (this was not our account at the time). When we arrived we noticed the almost brand new boiler front was melted as was the burner. This was the direct result of the exhaust fan back-drafting the boiler. The exhaust fan has been made inoperable since 1985.
  • Jellis
    Jellis Member Posts: 228
    I would be curious of the combustion numbers as well.

    available combustion air an issue?
    Had customer that would remove the access panel before i arrived which i thought was just the doorway into the boiler room and open all the time. After I would leave he would replace the panel door and the unit would go off on reset shortly after.
    vent in the panel and problem solved the issue.

    The problem is not always where you have found it before!

  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    A loose neutral wire in the service panel will allow 220V on the 110V system that are on different panel busses. This would fry all 110V things plugged into the receptacles.

    Look for higher voltages than the ratings on the device. Grounding problems could cause higher current draws.
  • DZoro
    DZoro Member Posts: 1,048
    Follow from your oil furnace/boiler (don't know what you have) the power wire directly back to the circuit breaker box, and to its own breaker. Making sure that there is no other wiring involved, and it is a true dedicated circuit. Then confirm line, neutral and ground are all reading there correct voltages, and groundings.
    That wire should not stop at any junction box, it should be a direct run. Confirm all connections are solid.
  • retiredguy
    retiredguy Member Posts: 915
    If this is a direct spark oil unit, make sure that the Ignition transformer lead/leads are not coming in contact with the cad cell leads. That will also quickly ruin a UV detector
  • ScottSecor
    ScottSecor Member Posts: 863
    @northernboiler any updates?
  • SeanBeans
    SeanBeans Member Posts: 520
    @STEVEusaPA knows that oil!!