Yearly Maintenance on AFG


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Old 11-06-09, 08:04 AM
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Yearly Maintenance on AFG

Hi Folks...been lurking here for years, but just now registered. I've learned a lot already, and thank everyone for their great sharing of knowledge.

I have a SlantFin Boiler with an Beckett AFG oil burner. Pretty standard tankless setup with remove 70 gal HW tank and 3 heat zones with separate pumps and a HW-priority-based zone controller.

I've been doing my own yearly maintenance for a couple years now, and I wanted to run my procedure by the team here and see if anyone has any additional advice.

I have an old-school Bacharach test kit for testing/adjustment. Got on Ebay for $120 (needed CO2 tester rebuild kit), which paid for itself first use I figure.

Here's what I usually do:

Before starting, check flue temp, overfire draft, smoke, and CO2...record for before/after comparison.

1) Change oil filter and clean filter housing (usually quite clean but I wipe it anyway)

2) Check fuel pressure with a regular pressure gauge, set to 100psi, +/-5 (only needed adjustment once).

3) Pull nozzle assembly and clean. (replaced nozzle last year to factory spec).

4) Clean and reset electrodes (also replaced last year, kinda rounded)

5) Haven't touched CAD cell, but will clean this year (had a recent random lockout, but reset it and burner seems fine by all measures). Will get a replacement to keep on hand...burner is going on 15 years old.

6) Clean and vacuum heat exchanger with factory brush. Used Soot Saber on first cleaning, but haven't needed it since.

7) Remove and inspect/clean/vacuum flue. Usually pretty clean. Has 6" Metalbestos chimney to roof (see question below).

8) Clean and vacuum firebox. Usually pretty clean. I get some red crud in the bottom which I assume is fuel related.

9) Button everything up, and test fire

10) Check/Set overfire draft to spec (usually fine)

11) Smoke test across a range of air shutter settings, look for minimum smoke condition, open a little more.

12) Check flue temp and look for reasonable reduction before/after...maybe 50F as I recall.

12) CO2 test with liquid Bacharach tester. Tweak air if needed. I usually can't quite reach factory CO2 spec (don't have data in front of me...I think the spec is 12, and I get 11 1/2 or so as I recall)

13) Feed my woodstove so I don't need the boiler anyway... Beer 4U2

This year, I'm planning to downfire the burner with a smaller nozzle (1 GPM to .7 GPM). My boiler spec's a smaller nozzle as an option, and actually doing that makes it Energystar.

Reason for downfiring is I get only 2-3 minute burner cycles which seems short to me. Hoping smaller nozzle drives a little longer cycle and a little more efficient operation.

A few questions (sorry for the long post):

A) My burner parts guy recommended changing the oil strainer in the pump. My cartridge filter is usually pretty clean, so I haven't worried about the strainer clogging. Is that something that needs regular changing?

B) I read a few posts about the pump shaft coupler going bad. Should I change it? I'll get one this year to have on hand...but I'm thinking let it run to fail.

C) Does the chimney ever need cleaning? Its usually pretty clean, but has some buildup over the years.

D) Any other common failure modes I should be addressing?

E) Any other advice anyone?

Thanks!!
 
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Old 11-06-09, 09:11 AM
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Pressure vs. Oil Flow Rate

One other question...

What does the group think of slightly lowering oil pressure as way to further downfire the burner a little more?

I'm thinking setting it for about 90 PSI, to get a further 10% reduction in oil flow. This would drive about .63 GPM from a .70 GPM nozzle.

I think these kinds of nozzles operate in a sub-sonic mode so flow rate is relatively proportional to pressure. Anyone have any experience with this?

Might be a mute point...I'll see what the burn time is with the .7GPM nozzle. If its say 3-4 minutes, I'll probably stop there...Beer 4U2

Thanks!
 
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Old 11-06-09, 05:25 PM
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Pump Screen/Pump Pressure

Do not drop the pressure below 100#. To do so will really foul up the spray pattern. BTY, pump pressure to flow rate is not a one to one relationship. http://www.delavaninc.com/pdf/total_look.pdf
The whole booklet is interesting but if you look on Pg. 13 there is a chart on pressure vs. flow rate.

The pump screen should at least be inspected. My standard for replacement is: If there is anything on the screen it gets replaced. A new gasket should be installed anytime the cover is removed. Gaskets come with the screen but can be purchased separately.

Pump couplers usually last a long time but they are cheap so keeping one on hand is fine.

Look up the chimney with a mirror on a sunny day. That will tell you if the chimney needs cleaning or not. On a modern burner it's very rare to have to clean a chimney especially on a factory built chimney.

Sounds like you do a good job. Keep it up.
 
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Old 11-08-09, 02:21 PM
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Thanks Grady.

100 PSI it is. Makes sense...didn't know the nozzles roll off under 100 PSI. Glad I asked!

Anyone know what the best burn time is for "peak efficiency" (I know that's subjective). Mine runs 2-3 minutes per cycle which I wouldn't call "short cycling" but seems on the short side.

For checking the CAD Cell, I saw a few posts that indicate it's good if its under 400 ohms with a bright flashlight, and over 4000 ohms in the dark. Does that sound right? I'll test when I do the PM next week...

Any other suggestions for yearly maintenance items on the burner?
 
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Old 11-08-09, 02:46 PM
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Burn Time

Burn time is going to vary with outdoor temperature.

I prefer to check a cad cell under operating conditions. In the dark the resistance should be greater than 20,000 ohms. With the burner running you should read less than 1,000 ohms (less than 800 is preferable). I often see cad cells showing around 400 ohms.
 
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Old 11-11-09, 04:23 AM
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Thanks Grady...I'll check the CAD cell in place. Sounds easier anyway.

What's the best way to temporarily jumper the controls to do this test? I recall seeing that attaching a resistor across after ignition is one way. If so, what resistor value?

Any other methods? It has a standard Honeywell control with only the red button (no LED's)...about 10-15 years old.

Thanks....
 
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Old 11-11-09, 01:57 PM
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It will run better at 130 PSI and a .75 nozzle
 
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Old 11-11-09, 02:43 PM
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Checking cad cell

You don't need a resistor. A simple jumper will do just fine. In a pinch, I've been known to use a paper clip.

What is the model number of the boiler? I can check Beckett & Slant Fin's websites for any updated nozzle/pump pressure info.
 
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Old 12-14-09, 09:25 AM
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I forgot to write down the specific model for the AFG burner...will get that tonight.

The boiler is a SlantFin XL-2000 XL-30 model. I believe the XL-30H is the identical boiler with a .85GPM nozzle and EnergyStar rating. I've been using the 1GPM nozzle spec'ed for the XL-30, but this year switched to the .85GPM of the XL-30H at 100PSI.

Can anyone verify that the only difference between an XL-30 and XL-30H is the nozzle? I recall reading that here a while back, but never saw it in black and white...

The CAD cell measures between 750-850 ohms while running (with the 1GPM nozzle...haven't checked yet with the .85GPM). I swapped in my new spare, and its about the same. So I'd say its good...but anything (besides the face of the cell) that I should clean to get it a little lower?

I'll include a CAD cell check with the air band matrix I'll do tonight...so that's checking Smoke, CO2, and CAD resistance at 5-6 air shutter settings looking for optimal combustion.

I read somewhere that finding the lowest CAD cell resistance is one way to tune air settings, but never tried that. Anyone have experience doing that?
 
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Old 12-14-09, 10:09 AM
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A quick update:

According to this list on the Beckett web site: http://www.beckettcorp.com/scripts/o.../oemsearch2.pl

The XL-30 and XL-30H have the same burner specs, except for the nozzle (and different air settings in the SlantFin manual).

Does this mean there are no other changes to make beyond recentering the air setting?
 
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Old 12-14-09, 03:58 PM
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Cad Cell Resistance

Don't even think about making adjustments based on the cad cell reading. A nasty flame will show lower resistance than a clean flame.

Adjust for a trace of smoke, read CO2, add air to drop CO2 about 1%.

I did notice on Beckett's site, that your burner requires a delayed oil valve. Is it so equipped?

BTW: Nozzles are rated in gallons per hour not per minute.
 
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Old 12-15-09, 05:04 AM
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I was wondering why I was burning 60X more oil than normal!

How would I be able to tell if I have a delayed oil valve? Pressure gauge?

What you describe for setup is basically what I do. I check for smoke and CO2 at 4-5 air settings, try to find minimum smoke and maximum CO2, then increase air slightly to provide some excess air margin.

It's amazing how smooth and quiet the AFG is when its properly tuned. And the boiler stays nice and clean...only some wisps of soot as I brush the heat exchanger.

I can't believe that people think they can properly tune a burner by eye. The last "tech" that worked on mine tried that, and ended up 2 notches high on excess air. The AFG roared, and had high stack temp. It did stay clean, but was probably running at 60% efficiency. With some tuning, mine runs mid-80's%.

I'll get the burner info and check for the delay valve...
 
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Old 12-15-09, 05:44 PM
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Delayed oil valve

Since you now have smooth ignition, the simplest way to tell if there is a delay is: Does the fire light virtually at the same time the burner motor starts or is there a delay of a few seconds?

I don't care how poorly a burner is tuned, it will not cause a
60X increase in fuel usage. The only things I know of which will cause that is either a leak or a thief.
 
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Old 12-17-09, 08:12 PM
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Grady,

That 60X thing was a joke about the GPM vs. GPH thing...a little dry I suppose...

I'll try putting the pressure gauge back on and see if pump pressure corresponds to flame ignition. The delay I see is might be by design, as the burner runs well otherwise.
 
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Old 12-17-09, 08:37 PM
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60x

Duh, the 60X thing didn't even register as far as gpm vs. gph.
Good one. A bit of humor always helps when working on a perplexing problem.
 
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Old 12-18-09, 09:05 AM
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Speaking of tough problems...

I had another random lockout last night. That's 2 in the last 8 weeks.

I reset it and checked combustion...zero/trace smoke, 11.5% CO2, 350F stack, OFD at -0.02", Air at 6 (zero band) with .85GPH nozzle. Seems to be burning near perfect. CAD cell stays below 1000ohms (750 to 850 range typical).

I need to double check oil pressure, and check calibration of my gauge. But last time I looked it was about 100PSI +/- 5 or so.

I may check electrodes again, but they should be quite close to spec (I used the Beckett electrode setting thingy).

Any other ideas on a cause? Maybe my control is going bad?
 
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Old 12-18-09, 09:59 AM
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Intermittent problems --- don't you love 'em?

Usually they are something that is beginning to fail and will get worse over time until it quits working altogether.

You usually don't need to wait for that to happen, if you have sufficient skill and patience.

You can probably replicate this fault by repeatedly cycling the furnace until it quits. If you can observe the fault while it's happening, your chances of identifying the problem go up a lot.
 
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Old 12-18-09, 02:21 PM
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Beckett Electrode Thingy

I certainly hope you don't mean that orange piece of crap.
The best thing to do with them is to grind 'em into little bittty granules.
I will all but guarantee if you used it, particularly to set the 'Z' dimension, the settings will be incorrect.
 
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Old 12-19-09, 09:35 PM
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Beckett Nozzle Setup Plate

I use the stamped flat aluminum plate I got with a set of Beckett electrodes. My new spare set has one also. Has dimensions for the 5/32 gap, 1/16 offset, etc.

It also has a triangular front that seems like it's used to set the depth of the nozzle.

I'll try measuring the electrode spacing with a steel rule and see if I get different results. Also I noticed a post or two about tweaking the electrode tips with 2 pliers to get more accurate spacing...

I've noticed that newer AFG's have a more advanced HV power supply and controls. Does it make sense to consider upgrading mine? Is there a retrofit kit for older burners? If I'm troubleshooting a component that's going bad, I'd just as soon update it and be done for another decade or two...
 
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Old 12-20-09, 01:25 PM
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T-Gauge

The T-gauge is fine & you are correct in thinking the tapered part is for setting the nozzle set back (Z-dimension). It is also used for checking to insure the nozzle is centered in the end cone hole. Unless parts go bad, I wouldn't worry about upgrading except maybe to install a primary control which shuts off the ignition after it proves flame.
 
 

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