Strange oil burner operation

Ken1234

I have an oil burner with a L8148A aquastat and R4184 primary. It has been very reliable, but an odd occurrence recently popped up. If a warm spell is encountered, I shutdown the power to the boiler and heat with the wood stove. During colder temperatures I turn the power back on and continue as usual. However, the last time I did this, the boiler fired and then shut down after the 45 second no flame delay. No problem I figured and popped a new cad cell in. Same situation! But the strange part is if I press the reset button, the boiler continues it's normal operation without another shutdown. It only happens if I turn the power off and then back on, once. I'm baffled. Any idea what may be going on?

SuperTech

Even if it isn't the cause of the problem, you should replace the crappy R8148 primary control to a modern digital primary control with interrupted ignition and a 10 or 15 second trial for ignition.

In 2025 no oil burner should be operating with a constant spark primary control with a 45 second trial for ignition.

I recommended the Carlin 70200 set for 10 second trial for ignition and interrupted ignition. It also has diagnostic features that will assist with troubleshooting problems.

EdTheHeaterMan

I agree with @SuperTech on upgrading to the Carlin 70200 Pro (latest version) for 2 reasons. They have all kinds of additional features including diagnostics.  The other is that it cost less than the replacement R4184 (if you can even find it) or the L8148G that would be the alternate replacement back in the day. 

You have an ever more rare version of that old style Cad Cell relay. The R4184 is the 120 VAC version of the L8148. All that means is that they omitted the T T terminals on the control and jump them internally.

Series 80 controls are 2 wire 24 VAC

Series 40 controls are 120 VAC controls (no 24 VAC terminals)

I learned that in 1979 at oil burner school whey I also learned that series 10 controls were three wire 24 VAC controls that employed a starting circuit and a holding circuit in order to establish a longer differential on thermostats

And you could use a series 80 thermostat on a series 10 control by connecting the R and W on the thermostat to the B and the W on the series 10 control.

Honeywell did that just to confuse everyone that worked on heater back in the day.

HVACNUT

What made you think the cad cell eye was blind and couldn't see fire?

There's a plethora of things it could be. When was the last time it was serviced? Do you have a copy of the combustion report? Call a professional. The turning off and on is not the problem.

Grallert

All that about the control, yes. I'd have a look at the ignition system. What type of ignitor or ignition transformer do you have? Honestly it could be a few things. Do you get a smell when it ignites? Is there any delay at all?

Ken1234

Thank you for your helpful insight. When I ordered the CAD cell, I also thought it would be a good idea to get a spare primary control in case it failed at some point. As Ed guessed, the R4184 is no longer available (probably a good thing). So, I opted for a Honeywell (Resideo) R7284U electronic primary. Sounds similar to the Carlin unit and priced similarly. Will set the ignition trial for 15 seconds which is my preferred time rather than the insane 45 second delay. Will try to turn off the ignitor after flame and see how that works. As you may infer, I have limited experience with burners but learn and service all my household equipment. Always nice to have second opinions though! Thanks again!

Ken1234

I replaced the CAD cell because it can cause a timeout if it doesn't see flame. Even though it worked on successive firings it was an easy, inexpensive variable to replace. I got the electronic primary control in case the original one is the problem and from all I read, it seems to a good choice to substitute it in anyway.

I usually clean the burner after about 500 gallons of fuel have been used. I don't do it yearly as some years I only burn less than 100 gallons. It fires up with no delay whatsoever and has a nice flame. I've had various service people do the tuneup and none have ever used a combustion analyzer. One person had it so rich it clogged up a couple months later. It seems to be difficult to find someone proficient in a relatively simple task.

I still have the original transformer ignitor in the boiler and will replace it with an electronic one should it die. It may last much longer if the new primary turns it off after the fire lights. Nice feature.

Ken1234

Determined what the problem was. Since I bought the electronic primary, figured it would be a good idea to install it as it had many better features than the obsolete R4184. After installation, I fired up the unit and once again it lit but went out after the new 15 second delay. Hmm, strange. However, with the new primer, I could see what was happening. It wasn't detecting the flame even though it was present. CAD resistance was reading erratically around 40k, way too high. Looking at the schematics more closely, I noticed a nozzle heater circuit which is always active when power is applied to the unit. Bingo! My theory, based on my readings, is that the flame is not at full brilliance with a cold nozzle when I apply power and call for heat. After the flame comes on, the nozzle heats enough, in conjunction with the heater, to keep the flame lit on the next and successive burns. Case closed.

EBEBRATT-Ed

That is unlikely. Think your still going to have problems. JMHO

EdTheHeaterMan

Is it possible that the nozzle heater is blocking the light from the flame from reaching the eye?

Is it possible that the end cone is partially clogged with a carbon build up that is blocking the light from the flame from reaching the eye?

Is it possible that the fuel is really that cold to cause such a rich flame on startup that it is not as bright enough for the eye to see it?

I have run across burners that do not have a line of sight path form the flame to the eye location and therefore there is a wheel signal (Greater than 2000 Ohms) and by adjusting the position of the eye bracket and painting the interior of a black air tube with silver paint, was able to get the signal to be much better. (Below 1000 Ohms)

Hope this helps, or you found what you needed. 

MaxMercy

https://forum.heatinghelp.com/discussion/comment/1850547#Comment_1850547

40K ohms is ridiculously high - too high in my opinion to be a nozzle heater issue. Even if it was running pig rich it wouldn't be that high. You don't mean 4K ohms, do you?

SuperTech

You have some other issue going on. Plugged flame retention head, bad cad cell eye or extremely poor combustion and and an unstable flame.

The cad cell eye doesn't just need to see a flame, it needs to be a bright, steady and stable flame or the burner will lockout on safety.

Ken1234

Based on all the comments, I pulled the gun out to give it a quick look and cleanup. The worst culprit was the flame retention ring. It was filthy, probably because of my short burn cycles (because of the wood stove) it may not get hot enough to burn off the carbon deposits. Shined up the air tube and tweaked the electrodes. Fired up immediately with the cad reading 400 ohms (was 1600, very marginal) on a steady burn.

Thank you everyone for your insightful information based on your years of experience.