13 month old draft hood rusting.

CCD

Help troubleshooting...

Draft hood on a gas fired Weil-McLain CGA5 is rusting on the inside after 13 months. The top of the jacket has a ring of rust particles falling from draft hood above it.. Looking up and into the draft hood with an inspection mirror, the 4" wide angled piece is oxidizing. The lower portion of the hood is fine. Beyond the the oxidizing piece on the draft hood there is a small spot of rust on the 6" elbow top.



Draft hood

Elbow

Motorized damper

5' of smoke pipe, EL, 2' of smoke pipe

Masonry, clay tile lined chimney



Is this a symptom of something larger?

Thanks in advance.

TonyS

Is it a outside

chimney?

The Steam Whisperer (Formerly Boilerpro)

Sounds like.....

the boiler is running too cold or there is a cold draft near the draft hood.  The common sources for a boiler running too cold is improper piping for a boiler in an old gravity radiator system or in a concrete radiant floor system.



Boilerpro

Tim McElwain

You have a combustion

issue which needs a professional to take a look at it. There should be a combustion test done. There should also be testing done to insure that the return water temperature to the boiler is not too low causing thermal shock and also cooling the combustion chamber causing  condensation.



Does this boiler have a pilot? If so is the knockout in the damper still in place, if so it needs to be removed.

CCD

Rusting draft hood

Tony thanks, yes it has an outside chimney.



boilerpro thanks, yes this is a converted gravity system. The boiler is located in an unfinished basement, really no cold drafts though.



McElwain thanks too, this boiler has an electronic start, no standing pilot so the knockout is in place.



The current W-M CGA-5 replaced a W-M VHE-5 which ran like a champ for 26 years.

The near boiler piping did not change from one to the other.



I'll hire a pro to perform a combustion test. Interesting, when I asked the W-M tech support, he asked was there enough combustible air? This is in a single family home, unfinished basement, 25' x 100' x 7' ceiling. When I got off the phone I thought maybe not enough combustible air?



Thanks all for the insightful feedback.

Mark Eatherton

Excess draft...

The box that you are looking at on the back of the boiler is a draft relief/downdraft diverter box. In some cases, the draft going up the chimney is excessive, especially in cases where the chimney use to service a solid fuel appliance. Under normal operating conditions, with the chimney pulling a strong draft, excess air is drawn through the open ended box, thereby super cooling the hot flue gasses and causing them to condense. When they condense, they become acidic and deteriorate metal components.



The solution would be to contact the National Comfort Institute and have one of their certified/approved contractors come out for a diagnosis and possible draft hood modification to alleviate the excess draft condition.



NCI can be reached at www.nationalcomfortinstitute.com



For the record, ONLY certified members of the NCI are allowed to modify the draft hoods on appliances to correct these situations.



ME

TonyS

Many times with an outside chimney

and a motorized vent damper, when the boiler is in the off cycle there is no longer any warm basement air going up the chimney, The chimney will get as cold as the outdoor temp. When the boiler comes on, the already low stack temps just condense in the chimney and can drip back down the flue pipe. If you have an outside chimney you must line it properly with an INSULATED liner and a drip leg or use a power venter. Otherwise the acidic  water vapor that's condensing will eventually eat away the chimney. The quick fix is to slide the button on your vent hood and let some of that basement air go up and heat the chimney just like a barometric check does on a oil boiler. But remember that is the heat you paid for.

Steve Ebels_3

In order of probability

(IMHO)

Boiler not reaching temp due to high mass system and no bypass in place.



Insufficient combustion air causing poor draft and/or some flue gas roll out.



Improperly sized chimney (diameter or height) causing draft issues