Extending the life of my current boiler.

rconkling

Good morning everyone,

New member, first post.

Ive done a bit of reading and learned a lot, thank you all.

We bought this house, built in 1929, last year in October. I've slowly been fixing issues with the boiler, thermocouple went bad, expansion tank was waterlogged, ect. All little things that I have learned about along the way. This is my first boiler so the learning curve has been a little steep, but I like to tinker, learn, and DIY.

The current set up is a c.1994 Dunkirk, 140k btu in, 112k btu output, in what I believe is a converted gravity system. Its a single zone going to 8 radiators fed by a Taco 007.

The main problem it has is that the water temp in the boiler only reaches 140* during the coldest days of the winter here in St Louis. Im baffled at how long this thing has lasted under the current setup.

I had a manual J performed last fall as part of a quote for replacement. They recommended the Lochinvar KHB085. But the cost was significantly more than I expected. So now Im on a mission to extend the life of the current boiler for as long as possible.

Id like to add TRVs, it needs a flue liner, last but not least Id like to add a Danfoss ESBE TVC or something similar.

At this point in the lifecycle of the system, is it a worthwhile investment to perform the work? Will the ESBE really extend the life of the boiler? Its made it this far with out one.

This is not our forever home, but we would prefer to keep it and rent it out when we move on.

Thanks for your insight

EdTheHeaterMan

This could have been installed better with a bypass to increase the return water temperature, however, It has been operating just fine for the last 26 years without one. This is typical of many plumber installed boilers in the late 20th century. Some operate just fine, others fail for the reasons you have read about. If you want to know about the condition of the heat exchanger, and if Flue Gas condensation has taken a toll on it, you will need to remove the sheetmetal cover and inspect the cast iron under the flue collector.

If it is in good shape, then I would leave well enough alone.

Mr. Ed

EBEBRATT-Ed

It's the boiler return temp you need to be concerned with, Below 130 ish for extended time can lead to condensation.

It's possible that with the low resistance of the gravity piping that you are "over pumping" the system. In other words a "normal" system will run about a 20 deg. diff between the supply and return you may be running 10 deg which would keep you above condensation.

I would be careful about adding TRVs without having boiler return water protection. The trvs may through the system out of wack and cause condensation.

I would start by getting and accurate thermometer on supply and return (or one thermometer) that can measure differential.

The return should get above 130 withhin 20 min or so from a cold start.

Checking the flue pipe and flue collector and top of the boiler sections for excessive rust and rot as @EdTheHeaterMan suggested is a good start

rconkling

Thank you

The gauge on top of the boiler is still fairly accurate. I compared it to my handled infrared thermometer and it was pretty close at the discharge point, where it almost never exceeds 140*. The differential was about 20* if i remember correctly, so the return is always below 130*.

There is definitely some corrosion, unsurprisingly.

rconkling

On a side note.

A guy that came to quote a replacement mentioned the most common reason for replacement was exhaust leakage around the flue collar at the top of the boiler.

Seems excessive to replace the entire unit for something that appears to be easy to R&R.

Any thoughts on this?

STEVEusaPA

Yeah, you're condensing. You could try to help that with a modern aquastat, or you're going to need a bypass (hopefully mixing valve) piped in.
I am curious like @EBEBRATT-Ed of supply/return temps while running. Infrared may not be accurate.

109A_5

What about the supply and the return being on the same side of the heat exchanger ? Apparently it is OK.

A converted gravity system would have a lot more water in it to heat up.



Manual

hot_rod

Get a quote on adding a thermostatic bypass valve. Although it might be time to think about a replacement. A boiler in that condition loses efficient also. No that you know what it looks like inside, it’s hard to ignore☹️

consider a CO detector as it could spill flue gas when heat exchangers start corroding like that

The Steam Whisperer

Many of these boilers last under these conditions because the heat exchanger heat soaks after each cycle. You can check this out by looking at the boiler temperature a few minutes after it shuts off, I bet it will be much higher than the temperature when it is operating. This is the design feature used by cast iron condensing boilers. This drys out the heat exchanger at the end of most heating cycles. I just use a simple boiler bypass to provide a warmer operating temperature boiler. Also, the pump needs to cycle off at the end of each heating cycles so the heat soak can occur.

The Steam Whisperer

Also, one more thing... That vintage Dunkirk is probably has one of the highest combustion efficiencies available for the simple atmospheric design. That was around the time that they upgraded the heat exchanger efficiency and still used the older, more efficient cast iron burners (lower excess air than the newer burners). I have a 1991 certified unit heating my home and added a stack damper to cut standby losses. Cleaning the heat exchanger and adding a stack damper will probably get you better efficiency than most newer similiar models, if you have the cast iron burners.

EBEBRATT-Ed

In my mind the corrosion you are seeing is pretty minor. Usually the "pins" on the boiler sections are the first to go. Your looks pretty good to me. The fire side of the boiler needs cleaning. I would clean the boiler and combustion test it first before I spend money on a valve. If it looks ok (combustion will be better with a hotter boiler) put a bypass valve on it as @hot_rod suggested and keep running it

EdTheHeaterMan

I was a little harsh on the original installer. Back when this was installed the I/O manual did not show bypass piping. The only mention of the possibility of Flue Gas Condensation , was on page page 6 top right column where they mention minimum of 120° minimum return temperature. This manual is Pre 2005 https://dunkirk.com/wp-content/uploads/2022/03/385_0.pdf

Not until after that, was there any mention of how to correct the low return water temperature problem with a ByPass piping arrangement with a diagram like this added to the I/O manual(s) on boilers manufactured after 2005. like this diagram.

I believe just adding the bypass with the indicated full port ball or gate valves to adjust the minimum return temperature as needed, is all that is required.

If you are going to the effort of installing the bypass, then you may as well add the Danfoss ESBE TVC or something similar while the boiler is drained. This way you can be sure the 120° minimum will be achieved in the shortest time frame.

Mr. Ed

The Steam Whisperer

Ed, that's interesting... that's a system bypass, where other Dunkirk manuals show a boiler bypass. I used the ESBE valves many years ago and had too many failures in a short time of life. I stopped using them when I saw that the boiler in a converted gravity system would get up to temp in about the same time as in a convector system if it had a boiler bypass.

rconkling

It does have cast iron burners, and the pump shuts off when the burners cut out. So it must be continuing to heat up.

The exhaust has a butterfly valve that opens when it fires up, is that the same thing as a stack damper?

Is there a good resource to show me how to clean the heat exchanger?

Appreciate your helop

rconkling

Now to Hijack my own threat

I have a larger reputable company giving me a quote for replacements.

He mentioned condensing boilers and their efficiency. How they need to be plumed with primary/secondary loops to keep the water temp up so the heat exchanger doesn't condense and rust out.

To which I said its a "condensing boiler" and need to be condensing to be operating at rated efficiency. He double downed on the primary/secondary requirement to keep it at the proper temp.

I read somewhere that condensing boilers need low return temps, but is there a temp that is too low? Thus necessitating a primary loop?

The quote specifies primary/secondary for the high efficiency boiler, but nothing about it on the standard boiler. It would be replaced as-is. Sigh.

mattmia2

Primary-secondary on a modulating condensing boiler is to keep enough flow through the boiler. On a converted gravity system you can probably do it without primary-secondary if you are careful with your math but it depends on the specific model of boiler because different types have heat exchangers with different flow resistance.

Some method of controlling the return water temp is critical with a conventional boiler with a converted gravity system.

Hot_water_fan

He mentioned condensing boilers and their efficiency. How they need to be plumed with primary/secondary loops to keep the water temp up so the heat exchanger doesn't condense and rust out.

That's utterly ridiculous.

I read somewhere that condensing boilers need low return temps, but is there a temp that is too low? Thus necessitating a primary loop?

I'd keep it above 32F but that's about it . The primary loop is to provide adequate flow.

JakeCK

Sounds like a salesman talking s*** out of his ****. I hope they employ more qualified individuals to do the actual work.

Like others have said the primary secondary isn't for temperature control, it's for flow. The key word we're looking for here is hydraulic separation. 

The Steam Whisperer

rconkling said:

It does have cast iron burners, and the pump shuts off when the burners cut out. So it must be continuing to heat up.

The exhaust has a butterfly valve that opens when it fires up, is that the same thing as a stack damper?

Is there a good resource to show me how to clean the heat exchanger?

Appreciate your helop

Cleaning is a pretty easy job. You have to remove the burners, the vent, top boiler sheet metal and the draft hood below. I use gun barrel cleaning brushes to clean between the pins. Then vacuum it all outof the bottom. It would be good to get it combustion tested. There's probably a video somewhere.

EdTheHeaterMan

This is the best video for your situation
https://www.youtube.com/watch?v=JvvluCaw-rI
At time stamp 6:11 in the video you can see the heat exchanger being cleaned with a brush and vacuum

rconkling

Well I took it apart to day to give it a good brushing and struck out. The only brush I could find is a little to big. I really need a 1"x .5" flat brush to get between the pins vertically. I cant run the brush at a 45, there are vertical baffles on the heat exchanger.

I also ran into another problem, the vent baffle has corroded away on one side. If it can be replaced ill swap it out, if not ill have to rivet a new flange on it. Though I havent been able to find anything like it online.

All in all, its in remarkably good shape, for the shape its in.

rconkling

I found the part # for the draft diverter, 425-00-675.

Havent been able to find one online. Anyone have a good resource for old parts like this?

I may just repair it.

TIA.

EdTheHeaterMan

That Heat eXchanger looks blocked. You will need to get the baffles out of the HX and thoroughly clean it. A lot will fall into the combustion chamber.

As far as the draft hood is concerned, is it one that looks like this?
There are companies that can make them from dimensions you provide. Look for sheet metal fabricators online.

The dimensions are important because the hight and diameters are designed to properly vent flue gasses. you can not make them shorter or change the diameter of the inlet or outlet. Weil Mclain had one that was 5" diameter inlet with a 4" diameter outlet after the hood. That boiler was approved that way and you never want to change it.

EdTheHeaterMan

R E Michel carries a brush from Mill Rose. RE Michel part number is 7M074. I don't know where else to get them. If needed I can get some for you if needed. PM me

rconkling

MikeAmann said:

rconkling said:

I found the part # for the draft diverter, 425-00-675.

Havent been able to find one online. Anyone have a good resource for old parts like this?

I may just repair it.

TIA.

Is this what you are looking for?
https://www.technicalhotandcoldparts.com/carrier-425-00-675-5-section-draft-diverter/

Possibly,

It says its a carrier part with no image, dimensions, ect, so ill have to confirm. Thank you

I found this company selling it as well. But they appear to be a liquidator and may or may not have it in stock.

https://www.radwell.com/en-US/Buy/UTICA BOILER/UTICA BOILER/42500675

rconkling

EdTheHeaterMan said:

That Heat eXchanger looks blocked. You will need to get the baffles out of the HX and thoroughly clean it. A lot will fall into the combustion chamber.

As far as the draft hood is concerned, is it one that looks like this?
There are companies that can make them from dimensions you provide. Look for sheet metal fabricators online.

The dimensions are important because the hight and diameters are designed to properly vent flue gasses. you can not make them shorter or change the diameter of the inlet or outlet. Weil Mclain had one that was 5" diameter inlet with a 4" diameter outlet after the hood. That boiler was approved that way and you never want to change it.

Its not blocked, the photo makes it look worse than it is. The baffles are part of the casting.

This is approximately what it looks like.

rconkling

EdTheHeaterMan said:

R E Michel carries a brush from Mill Rose. RE Michel part number is 7M074. I don't know where else to get them. If needed I can get some for you if needed. PM me

Thank you. Im running out of time to order brushes and parts. Doh. Its going to be in the 30s next weekend so i gotta get this thing back together by tuesday.

Im headed to Grainger first thing in the morning to see what I can scrounge up.

EdTheHeaterMan

I did not realize that you are calling the cast iron pins, BAFFLES

You should be able to get a coat hanger wire between those pins on a 45° angle. The brush you have should also fit. That really needs to be cleaner. This is an illustration of what I mean. each dot represents a pin in the cast iron. Not all dots are illustrated. See how the brush goes between the pins to get the heat exchanger clean.

Granger part number 2FCD7 should work
I have used 2FCD6 and 3EDP9.

.

EdTheHeaterMan

You might want to stop at home depot to see if they gave any of these. https://www.homedepot.com/p/DAP-10-1-oz-Black-High-Heat-Mortar-Sealant-12-Pack-7079818854/205030320. You will need only 1 to seal that draft hood. You can reuse it and seal it temporarily until a replacement can be procured.

rconkling

EdTheHeaterMan said:

I did not realize that you are calling the cast iron pins, BAFFLES

You should be able to get a coat hanger wire between those pins on a 45° angle. The brush you have should also fit. That really needs to be cleaner. This is an illustration of what I mean. each dot represents a pin in the cast iron. Not all dots are illustrated. See how the brush goes between the pins to get the heat exchanger clean.

Granger part number 2FCD7 should work
I have used 2FCD6 and 3EDP9.

.

Thank you. I understand how its supposed to look, but its not what my boiler looks like.
When I look straight down, after almost every other row of pins, there is vertical a ridge/baffle in the casting. Preventing me from running a brush past more than a couple pins at a 45.

I bought a brush similar to what you posted but its way too thick to run it vertically.

rconkling

EdTheHeaterMan said:

You might want to stop at home depot to see if they gave any of these. https://www.homedepot.com/p/DAP-10-1-oz-Black-High-Heat-Mortar-Sealant-12-Pack-7079818854/205030320. You will need only 1 to seal that draft hood. You can reuse it and seal it temporarily until a replacement can be procured.

Dunkirk calls for a cerafelt gasket, i bought something similar,

https://www.amazon.com/dp/B008HQ79DK?ref=ppx_yo2ov_dt_b_product_details&th=1

rconkling

Its a 3-4 week lead time to get a replacement draft diverter so I did a little repair work to get me through till the new one arrives.

EdTheHeaterMan

That will work... But you need to repair that rusted draft hood until you get a replacement. The high temp caulk will do a good job there. Kind'a like glue for the time being. Gravity is also a good way top keep that hood in place.

pedmec

I would frown from investing any money into that boiler. Those orifices on the cast iron burners start to open up due to rusting and will affect your combustion. You should perform a combustion test and check the CO readings before investing. Worked on plenty of those burners and once they have gone bad they are done. I haven’t been able to find replacements. Called multiple manufacturers with no luck either. 

Also you have flue gas condensation happening as evident by the rust. To correct that would require an invest that could be best used on a new boiler. Plus being an old gravity system with those low return temperatures your gonna be able to get a good return on your investment. Just not with the company that didn’t understand mod/con boilers 

rconkling

pedmec said:

I would frown from investing any money into that boiler. Those orifices on the cast iron burners start to open up due to rusting and will affect your combustion. You should perform a combustion test and check the CO readings before investing. Worked on plenty of those burners and once they have gone bad they are done. I haven’t been able to find replacements. Called multiple manufacturers with no luck either. 

Also you have flue gas condensation happening as evident by the rust. To correct that would require an invest that could be best used on a new boiler. Plus being an old gravity system with those low return temperatures your gonna be able to get a good return on your investment. Just not with the company that didn’t understand mod/con boilers 

I agree and would like a new boiler. But the total cost was significantly more than I expected based on what the boilers are listed for online.

So for now, im just limping this thing along on my own with very little money invested.

The burners appear to be in perfect shape with only mild surface oxidation. The edges are sharp on the orifices.

Plus, I'm hoping to utilize rebates from the new Homes Energy efficiency program, part of the inflation reduction act, to help cover the cost when I go the new boiler route.

If this was my forever home, Id be all in on a new boiler. But since I have no idea how long ill live here, its not cost effective to drop low 5 figures on replacement. If I can get a couple years out of this thing I can kick the can to the new owner.