Thread: Scorching at boiler cabinet

This is an older boiler unit but I was asked what would cause the scorching at the cabinet.
Would it only be due to the unit being old or would there be another issue with the system? Such as improper firing?

Any info would be helpful.

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That looks like a bad re-fractory in an oil fired boiler.

Was it oil?

No, sorry for the lack of info..
It is a natural gas fired boiler.

Possibly missing or damaged insulation or a breach in the combustion chamber. If you hit that spot with a laser thermometer while the unit is firing, you'll find the spot much higher in temperature than the rest of the cabinet. The discoloration is from excessive heat.

Way too much heat there. Could be disintegrated insulation, weird flame rollout, interior casing rusted away allowing heat and flame to go up that side. How knows.
There aren't many screws that hold those jackets together. Unfortunately they are usually rusted in place so getting the jacket apart can be a pain.
The thing is 50 years old, time for replacement anyway.

Yes, I recommended replacement.
It has had a good life

Thank you for the info..

I would tend to chalk it up to years of use just going on appearances alone. But I think that that is really irrelevant due to the age of the boiler which would be my primary concern.

After I report the findings on this gas fired boiler, My report would state....

The heating system was paced through it’s normal sequence of operating modes, with obvious defects noted at time of inspection. Due to systems age, it is clearly beyond it’s life expectancy, and replacement should be considered soon.

Why wait for "soon?" I'd recommend that it be considered now.

Originally Posted by Eric Barker

Why wait for "soon?" I'd recommend that it be considered now.

Because it's heating the home and working fine today. If it works today, why replace it today?

That cabinet rust may mean there is a leak over the boiler itself. It looks like an American Standard HW boiler and if it's 50 years old it is past its prime. A bigger concern would be water on the floor around the boiler or dripping onto the burners themselves that could indicate a section failure. I couldnt tell if it was steam or hot water but I thought I saw a Taco circulator. How is it vented? Thanks jack

Originally Posted by David Valley

Because it's heating the home and working fine today. If it works today, why replace it today?

If the cabinet is scorched like the one in Jon's pic, something is not working fine.

Someone please correct me if I'm wrong, but it's my understanding that a boiler that needs cleaning can overheat and show scorching.

If the boiler is a sectional boiler then the scorching could be where the insulation between the sections is missing in the area where the paint is damaged. The insulation can be replaced without replacing the boiler. A cast iron boiler can last a very long time if maintained properly.

Every combustion appliance has its own heat signature. This becomes apparent during the listing process when clearances to combustibles are established. At the temps. involved for ordinary residential appliance applications, you will not see external surface temps. sufficient to blister paint off. This is because the listing also anticipates incidental human contact with the exterior surface of the boiler/ heater. The CPSC would be flooded with complaints if it was normal for a heater to have a hot spot sufficient to cook off the paint as depicted in the OP's photos.

It is obviously an abnormal condition warranting further inspection and testing by a qualified contractor before use. Done.

Now, what is causing it? Who knows or cares, quite frankly. It could indicate overfiring, loss of external insulation, abnormal flame paths, etc. but the bottom line is, it ain't right and should be inspected by a pro.

Originally Posted by David Valley

Because it's heating the home and working fine today. If it works today, why replace it today?

David, I just said it should be considered. For me the question becomes how much do you want to put into an old heating unit that consumes more fuel than today's units. Of course your point of view is valid as well. My York furnace is over 20 years old with two small cracks in the front panel of the heat exchanger. I'm holding off on changing it out because I want to avoid a new furnace that has lots of finicky electronics.

Originally Posted by David Valley

After I report the findings on this gas fired boiler, My report would state....

The heating system was paced through it’s normal sequence of operating modes, with obvious defects noted at time of inspection. Due to systems age, it is clearly beyond it’s life expectancy, and replacement should be considered soon.

Originally Posted by Eric Barker

Why wait for "soon?" I'd recommend that it be considered now.

Originally Posted by David Valley

Because it's heating the home and working fine today. If it works today, why replace it today?

Because ... if it is so bad that you feel a need to state "replacement should be considered soon" (to cover your butt), then you need to cover your client's butt and just come right out and say that it needs to be replaced now.

However, if you feel it is "working fine today", then there is no need to say that it should be replaced soon.


You need to make up your mind and stick to your one decision: a) either it is "working fine", or; b) it needs to be replaced "soon" ... which is it?