Oil Furnace High Limit Lockout / Short Cycle / No Ignition?

coldguy23

My furnace has started having problems with short cycling or simply not turning on at all (when the thermostat calls for heat the fan will turn on but the burner will not).

Furnace has been blowing cold air 95% of the time since the end of last season. Cutting power to the furnace for an hour or so will reset whatever issue is causing this, but then it will usually short cycle.

I did partial yearly service for the first time in a decade (the landlord got it new in 2010 but never serviced it)- I replaced all filters (canister filter, oil pump strainer, nozzle filter, air filter), cleaned the nozzle, cleaned the probes and reset the gaps to spec, checked the transformer with the screwdriver, checked that the CAD cell was clean, checked the pump and bled the lines.

After this it fired right up and ran fine for 3 hours straight. I then powered down and restarted it 5 minutes later- no issues, fired right up again. Of course later in the day when it went from 65 to 30F outside and I actually needed it, the no-ignition problem is back again (I did not power down the unit in the interim). But since then it has also failed to fire up regardless of outside temperature.

It never goes into lockout (or at least not the kind that you can reset with the red button), but cleary the controller is locking out the burner from starting. Clearing it's memory by powering it down for a few hours seems to be the only way to reset it.

Since this is the R7184B it has no LCD screen to tell me what is wrong.
I suspect it is the high limit that is being tripped based on my research and the fact that the thing has not been cleaned since install and there is also restricted airflow. But I also suspect that the limit switch or controller may be bad since it takes powering down the unit for it to reset (I would assume a properly functioning system would still power up every time after cooling down and then just short cycle, rather than simply not initiating the burner ignition sequence).

Question:

How do I find what is causing the controller to refuse to start the ignition sequence?

(It is locking out but not giving me the flashing light, and going through the reset procedure by holding down the button does nothing. )

Does this model controller store fault codes and if so how do I access them?

Thank you all!


Specs:
Carrier 58CLA105-14112
R7184B Controller
Beckett AFG Burner w/Single Line Pump
Interior Oil Tank (Does not get cold)

STEVEusaPA

Your landlord should have a professional that knows what they are doing service it.
-13 years no heat exchanger cleaning?
-No combustion analysis

pecmsg

In most jurisdictions the landlord is responsible for providing minimum heat.

HVACNUT

Looks like the landlord doesn't get rent until a qualified oil tech gives it a clean bill of health. That's acceptable. 

MaxMercy

coldguy23 said:

Does this model controller store fault codes and if so how do I access them?


R7184B Controller

Yes, the R7184B does store codes but does not display them. For that, you need the "contractor tool" 52082 to read them.

I have both that controller and contractor tool on my home boiler, but mine has a known software bug that can't be repaired unless I replace the 7184 - when I try to go into settings with the contractor tool it causes the controller/burner to shut down and go into lockout - bummer. All I can really do is read the cad cell ohms when running. Beckett has a bulletin on it that describes the problem exactly...

https://beckettcorp.com/bulletins/genisys-oil-control-contractor-tool/

..but when I contacted them to tell them I'm having that particular problem, they told me "tough noogies".

I'm going to replace the Beckett R7184B and 52082 with what is a far better controller - the Carlin 70200 which does everything the Beckett R7184B does and more, and is self contained (no external reader required).

Honestly, if your landlord will pay for it, I'd upgrade to the Carlin 52082 anyway. For all we know, that will fix the problem. If it doesn't, at least you'll get trouble codes, a better controller, and it might just eliminate the controller as the issue.

If it fixes it, you still need to have this thing properly adjusted for combustion.

coldguy23

Thank you for the concern but the landlord provides electric heaters so there is no lack of heat.


I managed to locate the limit switch, which was not easy and was installed in about the stupidest place possible, under the sheet metal cover that they had aluminum-taped and screwed together and then behind the main circuit board and impossible to see with the borescope. Ironically there is an unused hole that accesses the same area of the heat exchanger cavity to the far left side of this area which is much more accessible- and this is where they showed the location of the limit switch in the manual (#10)




God knows why they didn't just put it there?!? I mention this only in case it helps someone else locate it.


Anyway it seems to be working fine. When I pulled it it was reading 0.1Ω. Heating it up with an indirect flame would cause it to open, and then it would close again after a short time. It appears to be working, but I know I need to test the temperature at which it opens. That's the next step. And I also plan to run the furnace with the limit switch bypassed and insert a K-type thermocouple probe in its place.

Assuming is it not defective- that just leaves the controller, correct? Even if the limit switch is damaged and is opening at a much lower temperature than it is specced at, this should result in short cycling, not complete ignition sequence failure...

I am assuming there aren't any other sensors that would prevent the startup sequence that I don't know about? The company doesn't even claim this model furnace on their website anymore so the manuals are all second hand, but the one I found only mentions one limit switch (but from my research I know some furnaces have multiple).

I am also assuming there is no secret lockout mode on the R7184B that requires special equipment to reset? Am I also correct to assume that since the controller does not fully reset after holding the button down for 45+ seconds, at which time it should attempt the ignition sequence, that means the controller is bad?


Thanks everyone who has offered advice so far. I will probably get the Carlin controller unless anyone can suggest anything else to check.

coldguy23

I bypassed the limit switch and am still having the blower runs forever/failure to ignite unless I turn off the main power for a while.

Definitely leaning towards a bad controller. Probably going to order the Carlin.

Unless there are other things that can cause a lockout on the R7184B that cant be reset by holding the button down for 45 seconds... There aren't any right?

Also how common are these Beckett controllers failing? What usually goes bad in them?

tyvm!

MaxMercy

coldguy23 said:

I am also assuming there is no secret lockout mode on the R7184B that requires special equipment to reset? </blockquote

Correct. A 15 second hold of the reset is required for a "hard lockout".

You can download the Beckett manual for your burner which covers all kinds of stuff including theoretical operation and troubleshooting.

https://5476519.fs1.hubspotusercontent-na1.net/hubfs/5476519/2022/Manuals/PDFs/Burner Manuals/Residential Product Manuals/6104-Burner_Manual_092120.pdf?__hstc=&amp;__hssc=

HVACNUT

Oh boy.

coldguy23

HVACNUT said:

Oh boy.

I am having trouble deciphering your cryptic answer.

So it is very common for controllers to go bad? Somewhat common? Rarely?

And does anyone ever crack them open and try to find what fails when they do go bad?

pecmsg

You never bypass a Safety. 

Use your meter to see if it’s doing it job. 

coldguy23

I never said I bypassed it and just walked away like "ok job's done". lol! That could be dangerous. However it is quicker to just eliminate it as a variable if I suspect the controller, rather than risk a limit switch that fails inconsistently.

I also wanted to see if the airflow was restricted, so I had to remove it to put a temperature probe in its place, and was logging the temperature during a test run to see if it passed the limit switch's rated shutoff temp.

pecmsg

Your meter will tell you the same thing with no risk. 

coldguy23

How would a multimeter tell me at what temperature the switch trips at? It would only tell me when it trips. I assume you are talking about an ohmmeter/continuity tester when you say meter...

I would argue my way is actually less risky, since I know what temperature the switch is rated at (195F), so as long as I don't let the chamber get over that point, its safe (or as safe as leaving the limit switch in place).

However a bad limit switch could theoretically check out on the meter but since I have no idea the actual chamber temperature I could erroneously rule out the limit switch while it is stuck in a closed state.

pecmsg

No
The reason is if bypassed $hit can happen and it’s forgotten!
So NO Never bypass a safety, use a VOM and measure!

coldguy23

So your solution would be what, just drill a hole next to the limit switch and insert the temperature probe there? And then cover it up with some tape after?

We bypass safeties all the time in industrial settings - but never without a LOTO system in place. In this case I am the LOTO since I am the only one who has access to the furnace and I removed the bypass right after the test, so even if I disappear tomorrow and someone else does come along later and flip the power back on, the missing limit switch would prevent it from igniting.

If anyone is interested it only ever got up to 135F (the limit being 195F). I was running a dual-probe thermocouple datalogger and the spot where the manual says to install the limit switch (along the left side wall of the HE chamber) ran about 10 deg hotter than the spot directly above the flame where the switch was actually installed.

rick in Alaska

What does that unit use for a fan/burner control? If it is like a Honeywell 4064 type, they area bimetallic control, and I have had them 'stick', and not close down all the way. Take the cover off and watch it while the burner is running. It should start turning while it is heating up, and then the fan will come on. Then it should turn back down after the burner shuts off, and finally shut the fan off. If it doesn't, then it needs to be replaced.
Rick

EBEBRATT-Ed

@coldguy23

I think your troubleshooting procedure is fine. As long as you know what you are doing when bypassing the safety and you do and then reconnect it after testing your fine.

coldguy23

rick in Alaska said:

What does that unit use for a fan/burner control? If it is like a Honeywell 4064 type, they area bimetallic control, and I have had them 'stick', and not close down all the way. Take the cover off and watch it while the burner is running. It should start turning while it is heating up, and then the fan will come on. Then it should turn back down after the burner shuts off, and finally shut the fan off. If it doesn't, then it needs to be replaced.
Rick

@rick in Alaska

I don't believe this model has any such part, although I am familiar with that device from other furnaces I have worked on, there is no mention of that in the manual and this furnace only has two access holes to the HE chamber that I can see- one for the limit switch (rectangular hole), and another round hole that is covered from the factory with a metal plate. I believe the 1158-110 board manages the internal temperature solely via timers, which I did find a bit odd, but I guess they did the math and know how long to run the fan to cool it off. (I assume during normal operation it gets a set time and a limit-trip gets a much longer time). However I have not found any manual or schematic on that board or its operation.

I would be interested to know why they decided to move away from that design. It seems logical to me that the control board should run the fan until a certain lower-bound temperature is reached, but what do I know.

Coincidentally I have narrowed the problem down to the control board, which I'm 99% sure has a bad relay (calling for heat activates the coil side of the relay but fails to activate the switch side which is directly responsible for controlling the open/closed state of T-T). I ordered a new relay and will be pulling the board in a few days.