Is there a typical part of an oil boiler that corrodes out first ?

Dave Carpentier

If you were asked to evaluate an oil boiler for remaining lifespan, where would you typically look ? Lets assume it appears to be operating normally.

Does condensation damage typically appear at the top of the exchanger first ?

EdTheHeaterMan

@Dave Carpentier You are asking for a reason... if you are looking at a boiler that has operated with low stack temperature and low return water temperature for many years, then the corrosion would eat thru the coolest part of the boiler exhaust path. Right where the cold return water enters and the flue gas exhaust leaves the boiler. depending on the boiler design that part may be the cast iron section where the vent connector pipe is connected to the boiler like the rear flue on a Weil McLain 68 or GO boiler. If there is a collector box that attaches to the top of the boiler then that part may fail before the cast iron fails like the Weil McLain GO top flue boilers.

I have also seen steel boilers with a bunch of rust in the fire tubes but very little soot. So Dave, can you be more specific on what you are looking at that made you ask this question?

Mr. Ed

Dave Carpentier

Well, Im not sure if Ive run mine on the margins. I suspect its quite fine, but how to tell ?
Its always been an "always hot" boiler (winter only), but the run times are not long, generally 8 or 9 mins. The supply water peaks 160 each cycle but will drop down to 125 or so before the next. So the question is in my particular case, is it condensing enough to damage ?
When I pop the lid off to do the annual cleaning, everything is usually quite nice... maybe just a trace of soots on the top of the exchanger and as far down in the grid as I can see. Ive never seen anything that resembles corrosion on the top part, but I certainly cannot see 100% of the tanks and tubes down further into the 'guts'.

Mad Dog_2

Its very difficult to tell, Dave.  Unless, there were tiny cameras mounted inside the passages and crannies, there really aren't any concrete methods to tell aside from thorough visual examination.  My philosophy is maintain as best as possible and run till failure (it leaks!)  Mad Dog

EdTheHeaterMan

If the burner operates enough to burn off the condensation, then you are fine. There is going to be condensation on every start up. How fast the boiler gets the flue gas above the due point is the question. a low stack temp and low return water temperature for 15 minutes is going to be a problem, especially if the burner only runs for 9 minutes...

If you open the boiler to inspect the flues and find no damp muddy soot with red tones mixed in, you are burning off all the condensation every cycle. You have nothing the worry about.

Mad Dog_2

Amen!  Mad 🐕 Dog