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New member needs help understanding boiler cycle for troubleshooting

GerryL Member Posts: 4
edited December 2021 in Oil Heating
Hi All, new guy here looking for info to help troubleshoot my Smith oil furnace used for baseboard heating. The furnace starts and runs fine when a call for heat occurs. It satisfies the demand, and the call for that zone clears. At this point the furnace usually goes through it's shutdown cycle for about a minute, but my lack of familiarity of what that entails is slowing me down. It sounds like the fire goes out and something continues to run. That 'something' that continues to run in the last minute now gets very erratic, starting and stopping.
Here is a link to a 1 minute video showing the problem. I started the video right when the call for heat cleared. This call was for domestic hot water.

It sounds like an electrical issue to me; possibly a bad contact or solder joint?
Thanks for reading!


    EBEBRATT-Ed Member Posts: 14,543
    Well that is a strange one.

    Could be the primary control (blue box on burner)

    Could be a limit control that is shutting the boiler off on temp.

    I don't think it's the burner motor

    Could be a loose wire.

    The first thing I would do is kill the power in the main panel take all the covers off the controls and trace out every wire hot & neutral and check for loose connections.

    Does this happen on every call for heat ends or just a DHW call?

    If you had an electrical test meter it would probably be easier to find
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,378
    Well that's scary. You'll need a competent oil burner tech to come in and figure it out like @EBEBRATT-Ed stated.
    BTW, you don't happen to have a power venter?
  • GerryL
    GerryL Member Posts: 4
    OK, to answer some questions I've only caught it and the end of a DHW call. BUT, I just turned up a house heat zone and watched it; no problems at shutdown. Then we ran enough DHW to make it call for heat; it was also fine at shut down this time. ??? Got to love the intermittent problems. I did pull all the control box covers and check all wire terminations and connections. I also gently tapped boxes and put very slight pressure on boards to see if I could induce a problem. I haven't found anything suspicious yet. I'll keep monitoring it. Oh, no power vent either.
    It has been serviced within the last year (normal cleaning, nozzle, filter). I'm fairly competent with test equipment, having worked my career in industrial and utility maintenance and operations. I'm not ready to call in the troops because it's intermittent. And because I had a rough service experience a number of years ago. We were struggling heating the house in a very cold winter, and I was working way too many hours, so we called for service to check it out. They did a normal service and said everything checked out OK. Still had trouble keeping house warm. Eventually when my work schedule slowed down I sat on a chair next to it watching it run. Ultimately I found 2 problems; the zone valve for my 1st floor was only opening partially. Also found erratic operation caused by a cracked solder joint at the base of a relay on the aquastat board. I resoldered that, and replaced the zone valve and it's been good since then.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,827
    edited December 2021
    “Ultimately I found 2 problems; the zone valve for my 1st floor was only opening partially. Also found erratic operation caused by a cracked solder joint at the base of a relay on the aquastat board.”

    Well done! Those would be a real challenge to find, especially the partially open zone valve. What brand was it?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • GerryL
    GerryL Member Posts: 4
    edited December 2021
    That was a Taco. And yes, it was a challenge. I think we went a whole season with it operating poorly. The next year I was convinced there was a problem; since I had it looked at twice already, I decided to get into it myself. I have to say, that was ultimately satisfying. Maybe I'm heading into another one of those projects. :)
    And I retired this year, so now I can camp out next to it if I have to.
    Alan (California Radiant) ForbesEdTheHeaterManMikeAmann
  • JK_Brown
    JK_Brown Member Posts: 24
    I'm a total amateur, but your video seemed to be of the burner blower running. And likely that there were several reignite/fail to sustain the flame attempts before it went out on lock out. Are you certain that the heat call satisfied? Or could the flame have been snuffed out and the oil burner tried to relight it?

    If the latter, have you added or increased your exhaust fans in the bathroom or kitchen so that they are interfering with the makeup air and natural draft for the boiler? I say this as you mentioned DHW which made me think that demand might accompany someone turning on one of those fans. Thus creating your intermittent.

    Or you might look at the flame proving circuit in the burner.

  • Zman
    Zman Member Posts: 7,496
    @JK_Brown he solved the problem.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,753
    edited December 2021
    Zman said:

    @JK_Brown he solved the problem.

    Lets still try to fix it anyway.... What questions should be ask next?


    That video sounds like a defective primary control. If you decide to replace the control I recommend the Carlin 70200 with a diagnostic display. (don't get the same one you already have.) It will help in solving other problems in the future. Also if the problem is not in the primary control, the diagnostic feature will help to pinpoint the problem.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    HVACNUT Member Posts: 5,476
    I can't see the burner too well but I don't believe that model Carlin primary offers post purge. And I can't see an oil delay valve or Clean Cut pump. 
    If there's no oil solenoid valve, then the chamber is getting oil, spark or no. 
    Keep a fire extinguisher and a low level CO detector nearby when you camp out.
    TT is jumped on the primary so there must be power at B1 in the aquastat whil this is happening. 
    Maybe the aquastat or thermostat on the indirect, or an intermittent short.
  • GerryL
    GerryL Member Posts: 4
    OK, I'm checking back in. After that last video and my probing and wiggling wires, it hasn't acted up (at least I haven't caught it doing anything strange). That said, I started wondering if lack of makeup air could cause this (and I think JK_Brown is suggesting this possibility by questioning fans). I did install a used wood stove in the basement (replacing a coal stove, which replaced a wood stove, which replaced a pellet stove, which replaced an earlier wood stove LOL). So you can see I've had a bunch of solid fuel heaters in the basement over the last 30 years; they all have had a separate flue from the oil boiler. BUT, we did put an addition on and added a wood stove upstairs a few years ago. Also, when I caught this happening it is because I was downstairs reinsulating my basement sill area and sealing up some drafts. Also, I think it was the first time both of these wood stoves were burning since sealing drafts. I should also mention that when it was doing that cycling I had my wife open the main house door to see if it stopped doing it. It didn't, but the unit did shut down within 20 seconds of opening the house door. I let the basement stove go out shortly after that video.
    So, with these cold temps coming this week I will refire the basement wood stove and monitor again. This could bring the AHA moment. If so, I assume I'll need to drill a hole in the house. I just don't know though, since opening the house door didn't stop it immediately. It almost makes me want to put together a microcontroller project with a pressure sensor outside and one inside to see if I'm pulling a vacuum on the house.

    Oh, to answer another question, yes the call for heat was satisfied. I was watching the zone LEDs. It always happens only during shutdown after call is satisfied; never at start or during run while still calling for heat.