AFG burner stops in the middle of the night.

babel17

The home heating system in my mothers house stops in the middle of the night about one night in three. If you hit the safety reset, it starts right up again no problem. Previously the burner motor that is integrated would also pop it's safety, but the local residential hvac shop changed that out with one that doesn't have a safety, charged a couple hundred bucks, and did absolutely nothing to solve the problem.

The system is an Ultimate Engineering PFO-4 Boiler with a Beckett AFG Burner. The Burner has a Honeywell R8184P control relay and a Honeywell L5158A Aquastat.

Based on just reading the manuals, I'd guess that the problem is the CAD cell or the control relay, but this isn't my field, so I'd appreciate some advice from someone with a bit more experience

HVACNUT

There's numerous things that could cause a safety issue. What you need is an experienced oil tech, not just an HVAC tech. Where are you located? Are oil companies sparse?
If Mom is alone, it might benefit her, and you to get a full service agreement with a reputable oil company. 24/7 emergency service. 

Mustangman

So middle of the night shut downs? Never during daytime? Does the boiler fire off right away when you re-set it? One thing comes to mind. This is going back a ways. Up until 20 years ago, the transformer had PCBs which we know is dangerous.. so the changed the whole transformer design with no PCBs. It had a flaw that drove tecs nuts for years.
The new transformer design has a internal thermal overload switch. I will take you thru a cycle so you understand what I am saying. Boiler gets a call for heat. Its not very cold out so the run times are shorter than when its 0 out. So the boiler is running.. on the front end of a cycle, your draft may not be perfect so you get some heat back up. In other words, your draft is not strong enough on the beginning of a cycle to keep heat from backing up against the burner. Remember the internal overload?? Enough heat backing up against the burner will shut everything down through the thermal overload. You go hit the re-set, and it runs flawlessly. Drives you crazy. You can't find anything wrong. Finally after a year or so of these phantom lock outs, I ran into a rep and he solved the problem by telling me about the transformer issues. The solution was go to solid state transformers. The old transformers were 10,000 volt the new solid state models are 14,000 and boy you can hear the transformer cackle as it arcs across the electrodes.
I am not sure how old your burner is. If its newer and has a thin little transformer, thats not the problem. If its big, bulky and heavy it may be worth throwing a new transformer on the burner. Since it never fails when you are there, Phantom lock outs are a bugger to figure out. FYI there is no warning signs for this problem. You can try getting it to fail by cutting the draft back and running short cycles.
Good luck

HVACNUT

Mustangman said:

So middle of the night shut downs? Never during daytime? Does the boiler fire off right away when you re-set it? One thing comes to mind. This is going back a ways. Up until 20 years ago, the transformer had PCBs which we know is dangerous.. so the changed the whole transformer design with no PCBs. It had a flaw that drove tecs nuts for years. The new transformer design has a internal thermal overload switch. I will take you thru a cycle so you understand what I am saying. Boiler gets a call for heat. Its not very cold out so the run times are shorter than when its 0 out. So the boiler is running.. on the front end of a cycle, your draft may not be perfect so you get some heat back up. In other words, your draft is not strong enough on the beginning of a cycle to keep heat from backing up against the burner. Remember the internal overload?? Enough heat backing up against the burner will shut everything down through the thermal overload. You go hit the re-set, and it runs flawlessly. Drives you crazy. You can't find anything wrong. Finally after a year or so of these phantom lock outs, I ran into a rep and he solved the problem by telling me about the transformer issues. The solution was go to solid state transformers. The old transformers were 10,000 volt the new solid state models are 14,000 and boy you can hear the transformer cackle as it arcs across the electrodes. I am not sure how old your burner is. If its newer and has a thin little transformer, thats not the problem. If its big, bulky and heavy it may be worth throwing a new transformer on the burner. Since it never fails when you are there, Phantom lock outs are a bugger to figure out. FYI there is no warning signs for this problem. You can try getting it to fail by cutting the draft back and running short cycles. Good luck

Or, you could use Occam's Razor. I'd place that test about 10th down on the list, if at all.
What about interrupted ignition? 

And can you show me a label that shows an igniter as having a thermal overload?

Too much heat pushing back against the ignition transformer or igniter would mean the boiler or furnace is plugged, or if a furnace, a cracked heat exchanger. On a positive pressure boiler...? 
The OP needs an experienced tech on site, not throwing darts from a chair. 

babel17

I appreciate y'all looking at the problem. I know intermittent problems are absolutely the hardest to diagnose, especially if you can't run tests. The problem furnace is in a rural area, so service contract is not an option. As far as "experienced techs" go, all the old boys that knew this stuff are long since retired, and the new kids appear to be just parts changers.
The Honeywell safety relay appears to be discontinued, so I'll put in the Beckett replacement and replace the CAD cell, and if that doesn't work I'll have her replace the entire furnace with a modern heat pump.

Long Beach Ed

Obviously the most common problem is that the fire is going out. When was the thing last serviced? If this was my boiler, and I had many that behaved the same way, I'd make certain the boiler was vacuumed and the draft properly set. Then I'd change the nozzle and filter and I'd blow out the oil line. The electrodes would be changed and the air tube cleaned. I'd properly set the combustion air, and do a combustion analysis.

This work should be done every year and whenever there is a problem with the burner. You simply can't troubleshoot a burner that has not been properly serviced.

This is exactly the work that should be included in an annual service contract. If you can't find someone to sell you a contract, well, the work still has to get done.

SuperTech

Wow. I never thought I would hear about someone replacing a furnace with a crappy heat pump because of such a simple problem. I could probably figure it out in 10 minutes, it's sad you can't find a decent oil burner technician. 

mattmia2

You need to find a good oil burner tech. Judging from your description the burner almost certainly isn't set up remotely close to right and at some point it gets the right conditions to lose flame altogether.

EdTheHeaterMan

I wish I could find an old article in one of the Trade Journals that explained a known problem with Honeywell's R8184 controls in the original design. (1980s) Since You have the R8184P (rare number no longer available) I think you have the removable gray metal cover, meaning that you have one of those original circuit designs. If that is the case, Just replace the Primary control with a new electronic model. Like the Beckett Genesis or the Carlin 70200 Pro.

That article mentioned that (and Honeywell would not admit to it) if there happened to be a power spike as a precise moment in the start up cycle on that control, that the diac or the triac on that circuit board could be compromised. Since this power spike phenomenon has to happen at a precise moment between the call for heat and the trial for ignition, it hardly ever happened. But once it did, that control will always have this problem. the control would get some bleed electric current to travel across the safety timer heater. Rarely did the bleed electricity ever heat up the safety switch enough to trip the safety switch, For that reason it was considered a non-issue by Honeywell and tech support just said ”that never happened before”.

Where the problem would manifest is if the compromised control had a call for heat for an extended period of time (like overnight during very cold winter days) that safety heater could get hot enough to trip. Now back in the day, the R8184 was the GoTo control for replacing the RA117A stack relay. It was the safer control because the safety timing went from 90 seconds to 45 seconds.

Today that safety timing is considered unsafe and all the electronic relays trip within 15 seconds if there is no flame signal from the Cadmium Cell eye. (also called the Cat’s Eye by some folks with selective hearing)

babel17

@SuperTech I wouldn't be replacing it because of this one simple problem, I'd be replacing it as this is just the latest in a long line of problems, and because of the poor design of the water system attached to it. It has hot water pipes running through an uninsulated slab. The thing is hellaciously expensive to operate compared to a modern heat pump.