Lars WH burners destroyed

bburd

This is the burner tray from one of two Lars natural gas fired commercial water heaters in a large condo building, over 100 units and about 15 years old.  There is a separate storage tank.

It was running fine at the last inspection in December. Our mechanical contractor found it in this condition yesterday and shut it down. They propose to replace the burner tray assembly and gaskets, restart it and tune the combustion.

Has anyone else seen this type of burner damage? The tech said the heat exchanger is undamaged, but it looks to me like a leak from above rusted out the burner tubes, which are probably aluminized steel.

Jamie Hall

I would want to check that over from A to Z after I replaced the tubes -- they may have been weakened by rust, but at some point along the line they burst. As in boom. And I'd want to know why.

EBEBRATT-Ed

looks more like a mini explosion to me

ScottSecor

I'm struggling to think what would cause this. We've worked on many on and installed many of those units.

I would certainly want to know how the tubes got that hot. I'd be checking the HX to see if its clogged, gas pressure, draft, flame signal, control operation, electric gas valve condition, etc. I

The more I think about it, I'm leaning towards way too much gas, blocked hx or blocked flue. At fifteen years, you may already be near the end of it's useful life expectancy.

mattmia2

I first was thinking it was burning inside the burner and melted it, but that seems unlikely that it would happen in several burners. The delayed ignition seems much more likely.

Does that just ignite from an igniter in the center above the burners? Is it a slow opening gas valve? Has it sped up over time?

bburd

Thanks to you all. I was trying to understand how so much damage could happen so quickly, and delayed ignition may be the explanation.

For what it’s worth, we have plenty of hot water; that hasn’t been a problem.

I wonder if we should just replace that boiler instead of repairing it, since it’s near the end of its service life. So is the steel storage tank unfortunately, which is giving us rusty water.

ScottSecor

I would think if it was delayed ignition, the refractory would be in bas shape. Imagine a cherry bomb exploding in the "firebox" of that unit. Each of the four roughly 3/4" thick insulating board that forms the firebox would be destroyed. That board is much easier to damage than aluminized burner tubes.

In my mind those burner tubes to the right were cherry red for hours or maybe even days to look like that.

Jamie Hall

The thing that bothers me is that unless I am being really misled by the pictures, those tubes burst from excess interior pressure. I quite agree that they may have been damaged previously -- overheated, rusted, whatever -- and that it may not have been a real explosion, but clearly there was an overpressure. And I'd want to know why.

Matt_67

I’ve seen that - in our case the unit was condensing in the heat exchanger and dripping on the burners. It was at a commercial facility that had added load and the water heater was no longer keeping up. Once the burners start deteriorating it doesn’t take long and they look like that.

bburd

Mystery solved:  the burners were replaced today. They are stainless steel, made in two layers with an inner distributing tube. The tech found that the welded seam on the bottom of one inner tube had failed, resulting in hot spots that deformed the outer tube; the problem then spread to the adjacent burners. He has seen this before, and said we were lucky to get 14 years of life out of the burners, which typically last 8 to 10 years.

That boiler typically does not last as long in domestic hot water applications as it does in space heating.

tim smith

I have seen similar failures on the tube in Tube design burners. The inner tube gets dirty slowing the flow of gas through burner, causes them to burn back inside the the tubes. Cooks them from inside out as they don't get cooled from air and gas passing through. That looks a whole lot like the original ao smith Genesis boiler. Rrrrrrr.
 When we service them we would remove burners and either blow out with air or wash them with clean water. Then shake out real well and reinstall.