Heavy Soot Buildup

What would cause heavy soot buildup on a propane gas water heater? The unit is a Reliance 606 / Model 640 YORS / Serial No. MO1107793. The pilot and burner were off, so I could not observe the flame color or pattern.

From the serial number, would I be correct in guessing it was built in 2001?

Wrong air mixture Call a gas mechanic.

Roy Cooke


and roy’s correct on the air mixture thing.

to add, was the soot just in the burner compartment, or spilled out on to the casing?

if it were outside the burner compartment, i would suspect improper or obstructed flue.

I was thinking that it was an improper air mixture. As a matter of fact the soot did spill out onto the outer shell. The owner made an attempt to wipe it off, but there were still signs of it on the shell.

The vent pipe on top of the roof looked O.K. could not get a close up because it was a metal roof. However, the vent pipe from atop the tank to the ceiling is not a straight run, instead it had a series of adjustable collars to route around the water inlet pipe to line up with the pipe going throught the ceiling. I would attach a picture, but I am having a bit difficulty.

Off the subject, when attaching photos is there a trick, when I click once or even twice on the Attach Image icon nothing happens.

look at the attatchment key section when you click “manage attachments”.
there are max dimensions and file sizes based on your file type.

if no window appears when u click “manage attatchments”, you may have a pop up blocker that needs to be turned off.

Thanks for the tip Chris, between turning off the pop-up blocker and resizing the photo, the image manager now see’s it. Now I just hope that it actually post!

1 elbow is all that would be necessary here.
the number of elbows here is silly, although it still looks like it may work.

was this pic supposed to show the “soot buildup”
if so, i dont see it.

if you are referring to the slight corrosion where the elbows meet the main flue, i would say condensation due to inadequate flue draw.

the warm air cools, condensates, then runs back down the flue before it has a chance to escape.

The picture was posted to show the unusual vent pipe configuration. I didn’t know if the configuration was akward enought to prevent good draft, which would possibly explain the bad air mixture causing the soot. The soot is at the bottom of the unit, and there was only a small amount left after the owner wiped it off. The heavy soot buildup was in the burner chamber. Couldn’t get a good picture of it. I did recommend to the client to have it examined by a professional gas appliance tech. The hot water heater had other issues (no TPR drain line, no drain pan). Thanks for the info.

Needs to be looked at by service professional

Reference Only

As per install book, that model code YORS is actually a nat gas tank (possibly a YORS w/ propane conversion installed w/o gas pressure spring adjustment?).

Model for propane should be HORS.


The model could of been HORS, the first letter of the model number on the tank was smudged so I could only take my best guess!

Thanks for your input

More than welcome Richard.

In above case and IMHO, HWH should be placed “Out of Service” until it is determined to be set up for use with propane.

When using standard Caution, Warning, and Danger (as seen often in manufacturer install books), IMHO, an unknown gas type / product set-up would fall in the Danger Category.

Revise my original - “Needs to be looked at by service professional” to “Discontinue use until looked at by service professional”.

Full Disclosure: I am not a Home Inspector, so I do not understand what SOP would be in this case, Just offering a humble opinion based upon my limited knowledge of the difference between Nat Gas and Propane properties.