Adjusting a Beckett AFG..
#1
10-20-08, 06:03 PM
Adjusting a Beckett AFG..
I've got a 3 year old Beckett AFG installed on my 1975 vintage American Standard boiler. It is under-fired for sure, Gross output, according to the mfg label on the boiler, is 190 MBH @ 1.7 gph or 170 MBTU @ 1.5 gph. I'm using a 1.0 gph (with an F3 retention head). I installed a new nozzle, filter, cleaned the boiler about 2 weeks ago and just got around to checking the numbers (w/Bacarach Fyrite Pro 125 and smoke tester).
CO 45 ppm
O2 7.3%
CO2 10.2%
EXCESS AIR 49.8%
STACK T 413 F
STACK DRAFT -0.04 (but fluctuates)
EFF 83.7%
SMOKE between 1 and 2
The smoke seems a little higher than it should be (and stack T lower). I know the latter is a function of how long the burner is running since stack T was still rising slowly when I saved the measurement (maybe 5 minutes).
I'm pretty sure the numbers I've gotten for previous years were more stabilized via longer run time although only the CO and stack T were much different.
CO 20 - 29
O2 6.9 - 7.1%
CO2 9.9 - 10.4%
EXCESS AIR 45.7 - 52%
Stack T about 460 F
Stack draft -0.01 - -0.03
EFF 82 - 84
Smoke 0 to 1
Is seems reasonable that an under-fired boiler might be more sensitive to firing time. I hate to bypass the aquastat relay to keep it running longer than it needs to. How long does the typical oil burner boiler take to stabilize? Should I open up the shutter a bit more?
CO 45 ppm
O2 7.3%
CO2 10.2%
EXCESS AIR 49.8%
STACK T 413 F
STACK DRAFT -0.04 (but fluctuates)
EFF 83.7%
SMOKE between 1 and 2
The smoke seems a little higher than it should be (and stack T lower). I know the latter is a function of how long the burner is running since stack T was still rising slowly when I saved the measurement (maybe 5 minutes).
I'm pretty sure the numbers I've gotten for previous years were more stabilized via longer run time although only the CO and stack T were much different.
CO 20 - 29
O2 6.9 - 7.1%
CO2 9.9 - 10.4%
EXCESS AIR 45.7 - 52%
Stack T about 460 F
Stack draft -0.01 - -0.03
EFF 82 - 84
Smoke 0 to 1
Is seems reasonable that an under-fired boiler might be more sensitive to firing time. I hate to bypass the aquastat relay to keep it running longer than it needs to. How long does the typical oil burner boiler take to stabilize? Should I open up the shutter a bit more?
#2
10-20-08, 06:29 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
Data
A boiler should reach at least 150º before taking combustion readings. Actually the higher the better.
This year's data doesn't look bad other than the smoke. You need to get it down to 0 - <1. I'm a bit surprised the CO2 is as low as it is. Even in old boilers I usually manage to get
11%+ but it might be due to the gross underfiring. Just for grins, you might want to play with different spray angles & paterns. I think in the Am Stds. I use a 70 or 80º 'A' (hollow) nozzle.
This year's data doesn't look bad other than the smoke. You need to get it down to 0 - <1. I'm a bit surprised the CO2 is as low as it is. Even in old boilers I usually manage to get
11%+ but it might be due to the gross underfiring. Just for grins, you might want to play with different spray angles & paterns. I think in the Am Stds. I use a 70 or 80º 'A' (hollow) nozzle.
#3
10-20-08, 06:55 PM
Mike, what spray pattern nozzle you using ?
What pump pressure you running ?
Dropping the firing rate that much will definitely drop the stack T.
How 'airtight' is the unit ? I wonder if you've got some dilution air sneaking in there ?
Grady, if he adds air to get the smoke down, won't the CO2 drop ?
How low can he go and still be OK ?
What pump pressure you running ?
Dropping the firing rate that much will definitely drop the stack T.
How 'airtight' is the unit ? I wonder if you've got some dilution air sneaking in there ?
Grady, if he adds air to get the smoke down, won't the CO2 drop ?
How low can he go and still be OK ?
#4
10-20-08, 07:08 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
Combustion Test Results
I didn't think about air leakage. 
It is certainly something to be considered.
Yes, adding air is going to lower the CO2 but I'll trade some short term efficiency for a clean burn any day of the week. As to how low can he go on CO2: Keep it as high as you can & still get a clean burn & reasonable stack temps but if it goes down to 9-9.5%, so be it. I think by increasing the firing rate he'd actually improve efficiency.
It is certainly something to be considered. Yes, adding air is going to lower the CO2 but I'll trade some short term efficiency for a clean burn any day of the week. As to how low can he go on CO2: Keep it as high as you can & still get a clean burn & reasonable stack temps but if it goes down to 9-9.5%, so be it. I think by increasing the firing rate he'd actually improve efficiency.
#5
10-21-08, 05:35 AM
Thanks guys. I had experimented with a few different nozzle patterns and settled on 80 degree semi-solid. From what I recall this nozzle seemed to give a more full looking fire. Pump is 100 psi. As for dilution, I did put in a new rope gasket after removing the breach for cleaning and re-cemented the side door so I don't think I have any major air leaks. I'll try cracking the shutter open a little bit more. It would probably be worth some further experimentation with nozzles....
#6
10-31-08, 05:02 PM
I finally got around to re-adjusting and got these new numbers (after running about 5 minutes)
CO 26
O2 8.8%
CO2 9.0%
EXCESS AIR 67.4%
Stack T about 449 F
Stack draft -0.04
EFF 81.6
Smoke 0 to 1
At least the smoke is down.
CO 26
O2 8.8%
CO2 9.0%
EXCESS AIR 67.4%
Stack T about 449 F
Stack draft -0.04
EFF 81.6
Smoke 0 to 1
At least the smoke is down.
#7
11-01-08, 09:04 AM
Are you able to check the draft over-fire? It may be on the high side which tends the pull the flame away from the head. That would result in the lower CO2 values. Just seems that it should be higher.
You noted in the first post that the flue draft was fluctuating. This is a sign that the fire isn't burning smooth.
Al.
You noted in the first post that the flue draft was fluctuating. This is a sign that the fire isn't burning smooth.
Al.
#8
11-01-08, 11:02 AM
It does still fluctuate. I've got a small viewport, maybe 3 inches diameter that has a metal cover (with a mach smaller hole so you can tell when fire is burning). I can pull this cover off to stick the probe in there and also can look at the retention head with a small dental mirror. However, removing that cover must affect the draft too...
#9
11-01-08, 12:44 PM
Is there a notch in the side of the viewport? Or maybe slide the cover over enough to insert the probe. Most boilers have an access of some nature to get an OF draft reading.
Al.
Al.
#10
11-01-08, 06:29 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
View Port
You can check the overfire draft thru the small hole in the cover. If the probe won't fit, drill out the hole until the probe fits without a lot of slop.
#11
11-01-08, 06:33 PM
Or crumple some aluminum foil around the tube and make a 'cork' and push it tightly in the hole.
My guess is that you've maybe downfired too far ?
Run the pump pressure up to 150 and run the tests again. With a 1.00 nozzle you'll be at around 1.25 GPH ...
You weren't running the F3 head with the 1.7 nozzle, were ya ?
Do you have any other heads ? ( an F4 or F6 )
My guess is that you've maybe downfired too far ?
Run the pump pressure up to 150 and run the tests again. With a 1.00 nozzle you'll be at around 1.25 GPH ...
You weren't running the F3 head with the 1.7 nozzle, were ya ?
Do you have any other heads ? ( an F4 or F6 )
#12
11-18-08, 05:37 PM
Hey dudes... I finally had some time to play with this set up again.
Before doing anything, I popped off the over-fire view/sample port cover so I could stick a dentist mirror in there and look at the flame. It didn't ever appear to be detached from the burner head. While making these observations, the burner cycled off. When it came on again several minutes later, I got a noticeable black/gray puff of smoke out of the port upon light off. This was accompanied by a definite diesel exhaust smell that my wife had been complaining about from time to time (CO detector in stairway of basement never went off though).
Anyway, I decided to try things at 150 psi instead of the 100 I was running. I figure better atomization has got to help a messy light off. It did help! I then re-tuned the shutter and fiddled with the barometric damper (on the stack) and came up with these numbers:
CO 53 ppm
O2 7.5%
CO2 10%
Stack T - 504 F
Stack draft -.05 but still fluctuates from around -.02 to -.06
Over fire draft 0.0 to 0.02
Effic. - 81%
Excess Air 51.9%
Smoke - 1
The flame does look larger and fuller as might be expected with the higher flow rate, efficiency is about the same as before despite stack T going up by 50 F. And like I said, it lights off without any noticeable smoke or smell.
What do you think of the over-fire vs. stack draft numbers?
Before doing anything, I popped off the over-fire view/sample port cover so I could stick a dentist mirror in there and look at the flame. It didn't ever appear to be detached from the burner head. While making these observations, the burner cycled off. When it came on again several minutes later, I got a noticeable black/gray puff of smoke out of the port upon light off. This was accompanied by a definite diesel exhaust smell that my wife had been complaining about from time to time (CO detector in stairway of basement never went off though).
Anyway, I decided to try things at 150 psi instead of the 100 I was running. I figure better atomization has got to help a messy light off. It did help! I then re-tuned the shutter and fiddled with the barometric damper (on the stack) and came up with these numbers:
CO 53 ppm
O2 7.5%
CO2 10%
Stack T - 504 F
Stack draft -.05 but still fluctuates from around -.02 to -.06
Over fire draft 0.0 to 0.02
Effic. - 81%
Excess Air 51.9%
Smoke - 1
The flame does look larger and fuller as might be expected with the higher flow rate, efficiency is about the same as before despite stack T going up by 50 F. And like I said, it lights off without any noticeable smoke or smell.
What do you think of the over-fire vs. stack draft numbers?
#13
11-18-08, 06:03 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
Combustion Test Results
The results don't look bad, not great but not bad either.
That puff of smoke & smell have me concerned. I'm afraid if the boiler is off a while you may either not get ignition or it will be really late resulting in a 'bang'. Are the electrodes set properly & the ignition transformer strong?
If you are still using that F-3 head, you are pushing it's limits. I wonder if going to an F-6 would make any real difference.
That puff of smoke & smell have me concerned. I'm afraid if the boiler is off a while you may either not get ignition or it will be really late resulting in a 'bang'. Are the electrodes set properly & the ignition transformer strong?
If you are still using that F-3 head, you are pushing it's limits. I wonder if going to an F-6 would make any real difference.
#14
11-19-08, 04:45 AM
I do have an F6 head I haven't tried yet. The ignition seems fine now at 150 psi. I'll be keeping an eye on it. When I changed the nozzle about a month ago the electrodes looked fine. I suppose it is possible the transformer is going bad. Can you test transformer output with a DMM?
#15
11-19-08, 06:07 AM
Please don't use the DMM on the ignition transformer. Although if you have a HV probe you could probably measure the output voltage. For ignition transformers (iron core or electronic) there is the screwdriver test. I prefer an alligator clip and keeping my hands away.
Set up an alligator clip on one terminal with a gap of about 5/8" to the other terminal. Then energize the transformer. The arc should go from the alligator clip to the other clip. It is goes anywhere else there is a problem. Dust and oil build up can cause the arc to go to ground.
Note the above where I mentioned keeping my hands away. It will knock you for a loop (10 - 14 Kv at 20 mA will bite like the gates of h....
Note that for the screwdriver test the spark should sustain at a 3/4" gap.
For the gray/black puff on startup, it may be that the cutoff in the pump is weak. This would allow oil out the nozzle before sufficient pressure is built up. An oil delay valve is the best way to go. It allows for pre-purge along with a sharp light-off and stop of the flame.
Al.
Set up an alligator clip on one terminal with a gap of about 5/8" to the other terminal. Then energize the transformer. The arc should go from the alligator clip to the other clip. It is goes anywhere else there is a problem. Dust and oil build up can cause the arc to go to ground.
Note the above where I mentioned keeping my hands away. It will knock you for a loop (10 - 14 Kv at 20 mA will bite like the gates of h....
Note that for the screwdriver test the spark should sustain at a 3/4" gap.
For the gray/black puff on startup, it may be that the cutoff in the pump is weak. This would allow oil out the nozzle before sufficient pressure is built up. An oil delay valve is the best way to go. It allows for pre-purge along with a sharp light-off and stop of the flame.
Al.
#16
11-19-08, 06:00 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
Transformer
You betcha they can bite & bite hard. I ONCE got in a hurry & didn't pay attention to the screwdriver I used. It happened to be one where the shank ran all the way thru the handle to a metal cap. When I went to test the transformer, my hand was wrapped around that metal cap.
That one was "only" an iron core which produced 10kv. The electronics run anywhere from 14 to 20+kv.
That one was "only" an iron core which produced 10kv. The electronics run anywhere from 14 to 20+kv.
#17
11-19-08, 07:16 PM
Well I've gotten zapped by automotive ignition coils a few times and so have respect for anything that spews high voltage. I'll try the visual test with alligator clip.
I'm still not sure about the draft numbers. Is it normal to have a positive draft over-fire? I'm reading 0.0 to 0.02. I just cleaned the boiler about 2 months ago so I'm pretty confident there's no restriction. Stack draft slowly fluctuates from -.02 to -.06.
I'm still not sure about the draft numbers. Is it normal to have a positive draft over-fire? I'm reading 0.0 to 0.02. I just cleaned the boiler about 2 months ago so I'm pretty confident there's no restriction. Stack draft slowly fluctuates from -.02 to -.06.
#18
11-19-08, 07:32 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
Draft
The one thing I don't like or trust about the 125 instrument is the draft reading. In my opinion it is totally worthless. If you want to know if you have draft or pressure overfire, hold a match or lighter flame up to the peep hole. Flame sucked in, you have draft; flame doesn't move (stays straight up), neither draft nor pressure; flame comes out away from the boiler, pressure overfire. If you want actual numbers, you have to use a draft gauge of one sort or another.
I use either an MZF or Draftrite & record those readings in place of the 125's readings on my print outs.
I use either an MZF or Draftrite & record those readings in place of the 125's readings on my print outs.
#19
11-20-08, 04:38 AM
I'm inclined to agree that the draft readings from the 125 are unreliable. I did the match test at the over-fire view port and it confirms pressure not vacuum over-fire. From a burning fuel and expanding hot gases point of view, it would seem that a slight positive pressure might be expected. Gotta look for one of those real draft gages...
#20
11-20-08, 07:17 AM
I don't believe that positive pressure on that boiler is a good idea. Unless there are seals on the doors and such there will be flue gas leakage. IOW, the boiler needs to have been designed for OF pressure.
For a draft gauge check out the Dwyer 460. Inexpensive and rugged.
Al.
For a draft gauge check out the Dwyer 460. Inexpensive and rugged.
Al.
#21
11-20-08, 11:49 AM
Thanks Al. I'm not sure what I'd do at this point to reduce pressure in the combustion chamber. It's still underfired at 1.25 GPH, the boiler, breach and stack are clean and unobstructed.... Stack dumps into a masonry chimney that is also clear (last time i looked)...
#23
11-20-08, 05:12 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
Stack/Overfire Draft
You have a stack draft of roughly -.04 & an overfire of +.01 on average. That gives us a drop of .05 thru the boiler which is an awful lot for that boiler, or so it would seem. What are the air settings on the burner?
Usually when you go to a higher capacity head (F6 instead of the F3) you can close the air down some. It might be enough to get you back to the negative side overfire. Maybe, maybe not, it's worth a shot in my book.
Usually when you go to a higher capacity head (F6 instead of the F3) you can close the air down some. It might be enough to get you back to the negative side overfire. Maybe, maybe not, it's worth a shot in my book.
#24
11-20-08, 06:32 PM
You might be onto something there Grady. My air shutter (the circular plate on the end) has the pointer at 9.5 - 10 and 1.25 GPM is at the upper limit for an F3 head. I won't hurt to try the F6. If I hadn't brushed out the boiler myself I would swear it was clogged up.. I did peek around in there with mirror and flashlight tonight and I still see the pins with no obvious carbon clogs. Maybe I'll open the breach this weekend for a reality check though... Grrrrr....
#26
11-20-08, 06:42 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
1.25 lol
I didn't even notice. I sure wouldn't want to feed that thing if it burned 1.25 gpm. 1.25 per hour would be bad enough. Mine is .75 & I'd go to .50 if the stack temp didn't drop so much.
#27
11-22-08, 06:33 PM
Success! I switched over to the F6 head and re-adjusted the shutter and got negative draft. During the changeover I did open up the breach and found no blockages. So I have to conclude this boiler just didn't match the air flow characteristics of the F3 head. The only difference I can see between the two heads are larger slots in the outer ring of the F6. Must be something to do with air velocity coming through these or maybe just proportionally more air in the outer portion of the head... New numbers are:
CO 31ppm
O2 6.8%
Stack T 467 F
Eff 82.5
CO2 10.5%
Excess air 44.7%
Stack draft -.06 to -.09
OF draft -.02 to -.04
Smoke between 0 and 1
CO 31ppm
O2 6.8%
Stack T 467 F
Eff 82.5
CO2 10.5%
Excess air 44.7%
Stack draft -.06 to -.09
OF draft -.02 to -.04
Smoke between 0 and 1
#28
11-22-08, 07:22 PM
This is with the 1.00 80° W nozzle ?
Can you not get zero smoke ?
When you were experimenting with nozzles, did you try a hollow (A) ? Last time I experimented with nozzles on my system, I found that with the B nozzle I could not get zero smoke. It would go to a trace but no further amount of air opening would knock it down ... I switched to the A and it went right down to zero smoke ... the flame was a little wider though, and was 'licking' the walls, so I put the B back in. At 150 PSI, the hollow nozzle seems to get wider flame... if you try the A nozzle, step it down to a 70° ... that's gonna be my next step.
Can you not get zero smoke ?
When you were experimenting with nozzles, did you try a hollow (A) ? Last time I experimented with nozzles on my system, I found that with the B nozzle I could not get zero smoke. It would go to a trace but no further amount of air opening would knock it down ... I switched to the A and it went right down to zero smoke ... the flame was a little wider though, and was 'licking' the walls, so I put the B back in. At 150 PSI, the hollow nozzle seems to get wider flame... if you try the A nozzle, step it down to a 70° ... that's gonna be my next step.
#29
11-22-08, 07:35 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 16,321
Received 38 Upvotes
on
30 Posts
Try to adjust the barometric draft regulator for a bit less draft on the outlet. This will allow you to give the burner a bit more air and clear up the smoke and lower the CO.
#30
11-23-08, 06:32 AM
Thanks Furd. I think there's room to back down on the draft regulator. It was also quite windy yesterday so that may have been biasing the reading.
NJ, I don't think I ever tried a hollow nozzle in there. Probably because the old burner I replaced used a solid. I am still using the 1 GPH (@100 psi), 80 degree semi-solid. It sounds like it would be worthwhile to try a hollow. I think I'll stick with this flow rate (1.25 GPH at 150 psi) and the F6 and try a hollow at 80 and if too wide, a 70. It's a lot easier to change nozzles than heads...
This is getting to be hobby...
NJ, I don't think I ever tried a hollow nozzle in there. Probably because the old burner I replaced used a solid. I am still using the 1 GPH (@100 psi), 80 degree semi-solid. It sounds like it would be worthwhile to try a hollow. I think I'll stick with this flow rate (1.25 GPH at 150 psi) and the F6 and try a hollow at 80 and if too wide, a 70. It's a lot easier to change nozzles than heads...
This is getting to be hobby...
#31
11-23-08, 06:45 AM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
Hobby
Be careful Mike. This "hobby" could turn into an obsession.
Don't believe me? Ask NJ Trooper. He came here a couple years ago with a question & listen to him now.
Don't believe me? Ask NJ Trooper. He came here a couple years ago with a question & listen to him now.
#32
11-23-08, 10:18 AM
It's all youze guyz fault !
I can not tell a lie though, I was kinda 'pre-disposed' ... my background precedes me...
Ya know who gots it worse than me though ? my vote goes to OldBoiler ... now HE's a SERIOUS hobbyist! Check that O2 sensor he's got on-line ...
I'd go right for the 70 and go to the 80 if it's too narrow ...
I think you'll like the 70 better ...
Another big thing I noticed going from the B to the A :
With the B, the boiler go 'BOOM' when it lights. BaroDamper bangs. This boiler has done this for 25 years. With the A, it's a MUCH smoother light off ... almost silent comparitively.
I can not tell a lie though, I was kinda 'pre-disposed' ... my background precedes me...
Ya know who gots it worse than me though ? my vote goes to OldBoiler ... now HE's a SERIOUS hobbyist! Check that O2 sensor he's got on-line ...
try a hollow at 80 and if too wide, a 70.
I think you'll like the 70 better ...
Another big thing I noticed going from the B to the A :
With the B, the boiler go 'BOOM' when it lights. BaroDamper bangs. This boiler has done this for 25 years. With the A, it's a MUCH smoother light off ... almost silent comparitively.
#33
02-02-10, 03:42 PM
Member
Join Date: Feb 2010
Posts: 1
Upvotes: 0
Received 0 Upvotes
on
0 Posts
Buuuuurrrrrrrr
Hello, I am new this is my first post but, Let me lay one on you.
My Beckett AFG breaks down EVERY year. Mostly the same symptoms give or take. This time is no different... runs for about 20-40 seconds with flame for about 10, then dies.
They only way I keep my pipes from freezing in the last couple days is to run with the front view hole open and let it heat up. I assumed this was a venting thing, but I am not sure.
The nozzle assembly hase a LOT of soot on it, and there is black smoke coming out of the chimney outside, which is scaring the s#!t out of me.
I cleaned everything and tuned up as well.
ANY help, will save me, as I am broke and can't afford a prof. at the moment. Thanks.
My Beckett AFG breaks down EVERY year. Mostly the same symptoms give or take. This time is no different... runs for about 20-40 seconds with flame for about 10, then dies.
They only way I keep my pipes from freezing in the last couple days is to run with the front view hole open and let it heat up. I assumed this was a venting thing, but I am not sure.
The nozzle assembly hase a LOT of soot on it, and there is black smoke coming out of the chimney outside, which is scaring the s#!t out of me.
I cleaned everything and tuned up as well.
ANY help, will save me, as I am broke and can't afford a prof. at the moment. Thanks.
#34
02-02-10, 04:04 PM
I don't know that we _can_ help... there is no 'crash course' on burner repair/maintenance...
The black smoke means there is something seriously wrong with your combustion. You could have a clogged up nozzle, your boiler could be plugged up with soot, there's tons of things that could be wrong...
When was the last time that the burner WAS serviced by a tech?
The black smoke means there is something seriously wrong with your combustion. You could have a clogged up nozzle, your boiler could be plugged up with soot, there's tons of things that could be wrong...
When was the last time that the burner WAS serviced by a tech?
#35
02-02-10, 07:13 PM
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,667
Received 39 Upvotes
on
37 Posts
Details & pix?
Can you give us some details about the burner & boiler such as make, model, firing rate (nozzle size), & burner settings? Pictures almost help. You can post them on photobucket.com or similar site & provide a link here.
#36
02-05-10, 05:37 PM
It's sounds to be running very rich from what you describe. Have you ever had the boiler opened up and cleaned? The heat transfer passages can get very clogged up with soot over years of not doing this regularly (I do mine every year). Usually there is some sheet metal to be removed and an access door which allows a boiler brush to get in there and remove the crud. It's a seriously messy job and you'll need a shop vac with a HEPA filter to remove all the residual dust (a regular paper filter will pass some of it right through). If you are sure the boiler has been properly cleaned, is it possible someone closed the air shutter by accident?
