# Sooted up boiler - no real cause found



## futz (Sep 17, 2009)

Got a no-heat call from a sort of regular customer on New Years day. The pilot is out and he can get it relit, but it just blows out again - and he says the flame is coming out the front!  Oh oh! He's ok with the gas fireplaces until I could get there today. So today I get there and see that the boiler has been spilling out the front and has melted the control wiring and the tridicator lens and finally knocked the pilot flame out . "Oh! This not be cheap!" 

The cooked wires had shorted and killed the transformer in one of the two fan centers, so before even touching the boiler I have to rewire and replace a fan center.

Then the boiler - a crappy Allied Super Hot MG-100 steel boiler. I remove the draft hood and vent and can see that the heat exchanger is badly sooted up. The vent has some in it as well, but not so bad.

I burn home and get a compressor and vacuum and parts and wire. Then I pull the whole top end apart and find I can't get anything through the heat exchanger - it's too tight. So I use the compressor to blow the soot out and vacuum it up. Unbelievably filthy job - I'm black from head to toe.

Without taking the entire boiler out I can't tell if I have the heat ex fully clean, but I turn on the burner with the top off and feel around to see what's flowing and what's not. All seemed good except the rear center area, though that may well have been caused by the exhaust just finding the path of least resistance. Couldn't get it any cleaner without pulling it, and it's not spilling at all anymore (in fact, I can feel it pulling air in the front now) so I reassemble and put the vent back together.

Now the strange thing(s). I couldn't find a definite reason for the sooting problem. I did a careful checkout of the combustion air supply - all good. Looked for plugged burners, pet dander and other etc. causes - nothing. Then I thought since it wasn't "not enough air" maybe it could be "too much gas" - maybe the gas valve regulator has failed and is trying to shove 7" gas through the burners instead of 3.5". I put a manometer on it and it was running only a tad high - about 4". Not enough to explain the sooting. I toned it down to a nice solid 3.5" and kept looking.

I noticed that, while the flames were looking good, I was seeing some largish orangey and maybe possibly a bit yellowy flames at the back of the firebox. I pulled some burner tubes and had a look. They were nice and clean, but the end crimps of the middle ones had opened up (from heat I assume?). You could see right out the back of them. I squeezed them flat again with a pliers, but there's still a small gap. After reinstalling them the big flames were gone.

So what do ya think? Would those open-ended burner tubes cause the sooting? I'm afraid it's just going to happen again. Finding burner tubes for that old boiler is probably not possible. Maybe I could weld them up?

If it happens again I'm thinking of just selling him a new boiler and sliding it in under the old piping. There is room, and the original fitter left a couple unions. The old piping is atrocious, but it's worked all these years and a full repipe will be EXPENSIVE - just trying to save the customer some $$$. Of course I'll offer him the full rebuild as well - it also needs the old poly-b radiant piping isolated (another couple grand) to get a full life-span out of a new boiler.


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## uaplumber (Jun 16, 2008)

Sounds like a lazy flame in the back. That causes sooting up alot.
Having recrimped the tubes you probably fixed it.


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## trick1 (Sep 18, 2008)

If the large flames were impinging on the heat exchanger, the soot in the rear of the combustion makes perfect sense.

In situations such as this, I ALWAYS put a draft gauge at the breeching, before the draft hood, if possible. Checking draft after the hood can give a false reading.

The large flame thing that you said still sticks in my mind and I keep thinking impingement (flame touching the exchanger and cooling the flame, causing incomplete combustion and creating soot). 

It probably wouldn't be a bad idea to gat an analyzer on it and see what is actually going on combustion-wise.

In my experiences, draft problems account for about 80% of burner problems and the other 20% are usually lack of combustion air

Sounds like you're on the right track though:thumbsup:


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## futz (Sep 17, 2009)

uaplumber said:


> Having recrimped the tubes you probably fixed it.


I think you're right. I hope you're right.  I sure would have like to have crimped them tighter, and/or have had access to a spot welder. Would make me feel a lot better about it.

I'm going to watch my supplier's scrap pile for an old MG-100. Maybe I can snarf some better burner tubes for that thing. The outers seem to survive much better than the middle ones.



trick1 said:


> If the large flames were impinging on the heat exchanger, the soot in the rear of the combustion makes perfect sense.


Good, then I was looking at the right thing. I hate it when I can't find a good solid reason for a problem like that.

The last sooted up boiler I cleaned was a huge old apartment oil burner with retrofit natural gas burners added. The air intakes collected lint and dust until they were clogged off. Then the boiler and vent *filled solid* with soot. What a hideous job! Destroyed a big shop vacuum on that one. At least I could get wires and chains through the heat ex on that one though, and you could see light through the heat ex and could tell when it was clean.


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## Scott K (Oct 12, 2008)

Did you clock it ?

Also, - Lots of Superhot products are made in North VAncouver - maybe worth a call to see if they can offer you any solutions and/or replacement parts if needed.

We did this Boiler RE & RE this past Summer. We pulled out an old 1+ million 2 stage Superhot boiler and replaced it with 2 Lochinvar Knight 399's. I just remember having a huge laugh when we dumped off the old beast at the transfer station recycling center and immediately drove by the Super Hot factory down near the Second Narrows Bridge. 
"Hey, we just scrapped one of your boilers!" LOL


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## dankman (Nov 19, 2009)

I doubt it's the problem but have you checked the dirt leg for oil? I've run into a few situations where oil from the fuel source has created a problem like you are describing.


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## futz (Sep 17, 2009)

Scott K said:


> Did you clock it ?


No I didn't, and now that you mention it, that would have been a good idea. 

EDIT: On the other hand, why? Manifold pressure was checked and found to be good. And definitely nobody has changed the orifices. So why clock it? (Thought of all this while I worked this morning.)



> Also, - Lots of Superhot products are made in North VAncouver - maybe worth a call to see if they can offer you any solutions and/or replacement parts if needed.


I called them on another not-as-old boiler with a leaking heat exchanger. They were super helpful and even found me a replacement heat ex for it - no charge, though it was real old.

I suppose it wouldn't hurt to call them on this one and see what they suggest.



dankman said:


> I doubt it's the problem but have you checked the dirt leg for oil?


I didn't. Another good suggestion. I too doubt that's the problem, but it's another thing to check.


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## futz (Sep 17, 2009)

Ha! :thumbup: Found a MG-100 in the scrap pile today and pulled the burner tubes. They're all in mint condition. So as long as they aren't somehow different (they look right) then I'm gonna install them in the customer's boiler.


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