DHW coil in oil fired boiler

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Scottsman
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Post By: Scottsman » Fri. Feb. 16, 2018 6:34 pm

I've noticed a steady decline in the heat of my hot water coming from my oil fired boiler. Probably scale. I haven't cleaned or replaced it since moving here 10 years ago. It's a Weil McLain 62 series probably 40+ years old. Question: When I'm looking at this Honeywell limit control 6006A 1145 am I reading this dial right, that 160 is the low and 200 is the high? Or should I assume that the high limit is dead center (right now on 180)? -
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Rob R.
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Post By: Rob R. » Fri. Feb. 16, 2018 7:14 pm

180 is the high limit, and there is a differential setting inside the cover...probably set at 10 or 15 degrees. When the boiler cools to the high limit minus the differential, the burner will fire until the high limit is reached.

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Post By: Scottsman » Fri. Feb. 16, 2018 9:24 pm

So in theory, I might be able to get some hotter water out of this boiler by raising the limit to like 190? I looked at the price of replacement coils for a 62 series steam boiler and they are like $300 to $400 just for the part, not counting removing the old one, which could result in some snapped bolts with a boiler this age.

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Post By: Rob R. » Fri. Feb. 16, 2018 9:32 pm

Cleaning the coil would probably help more than anything.

If 180 degrees is not doing the job, the coil is certainly scaled up.

I agree that tearing into that coil on a boiler that old is a bad idea. Might be time to think about a separate water heater, and/or a boiler upgrade.

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Post By: windyhill4.2 » Fri. Feb. 16, 2018 9:37 pm

A water to water plate exchanger would likely be the easiest & lowest cost way to get the hot water you need.

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Post By: Rob R. » Sat. Feb. 17, 2018 6:32 am

That would be quite a project on a steam boiler.

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Post By: windyhill4.2 » Sat. Feb. 17, 2018 6:43 am

Rob R. wrote:
Sat. Feb. 17, 2018 6:32 am
That would be quite a project on a steam boiler.
I missed that part..
I just reread the first post & was going to ask where the steam part came in...
Then i reread the OP's 2nd post...

There it is....
Oops :oops:

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Post By: Pacowy » Sat. Feb. 17, 2018 8:58 am

Rob R. wrote:
Sat. Feb. 17, 2018 6:32 am
That would be quite a project on a steam boiler.
Wouldn't it be ok if you stay below the waterline? I have run an indirect and a hydronic loop with an air handler off of steam boilers.

Mike


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Post By: Pacowy » Sat. Feb. 17, 2018 9:02 am

And on a steam boiler, if that aquastat is really setting the high limit at 180, it's not likely to make much steam. Isn't that the low limit?

Mike

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Post By: Rob R. » Sat. Feb. 17, 2018 9:30 am

Pacowy wrote:
Sat. Feb. 17, 2018 8:58 am
Wouldn't it be ok if you stay below the waterline? I have run an indirect and a hydronic loop with an air handler off of steam boilers.

Mike
Sure, if that is what you want to do. By the time you get done cutting into the piping, buying the proper circulator, fittings, and plate exchanger, you will have quite a project. If hiring the job out - it would probably be less expensive to switch to a separate water heater. I still think cleaning the coil might give it a few more years of service for not a lot of money, but he won't know unless he tries it.
Pacowy wrote:
Sat. Feb. 17, 2018 9:02 am
And on a steam boiler, if that aquastat is really setting the high limit at 180, it's not likely to make much steam. Isn't that the low limit?

Mike
Yes, the aquastat controls the low operating limit of the boiler. 180 is the "high" of the low limit operating band. The pressurtrol is the real "high limit" on a heat call.

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Post By: windyhill4.2 » Sat. Feb. 17, 2018 9:40 am

Pacowy wrote:
Sat. Feb. 17, 2018 9:02 am
And on a steam boiler, if that aquastat is really setting the high limit at 180, it's not likely to make much steam. Isn't that the low limit?

Mike
There it is...
Now i know why i assumed it was a hot water unit..... the numbers weren't high enough !!

AND, i am so used to seeing a certain member posting about the "steam chest" on any boiler,that i just assume that is what some people consider a boiler..
So, it wasn't totally my fault for being steamed stupid. :lol:

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Post By: Pacowy » Sat. Feb. 17, 2018 10:28 am

Rob R. wrote:
Sat. Feb. 17, 2018 9:30 am
Sure, if that is what you want to do. By the time you get done cutting into the piping, buying the proper circulator, fittings, and plate exchanger, you will have quite a project. If hiring the job out - it would probably be less expensive to switch to a separate water heater. I still think cleaning the coil might give it a few more years of service for not a lot of money, but he won't know unless he tries it.
I agree that if cleaning will extend the useful life of the coil then it certainly should be at or near the front of the line. My comment was in response to your previous post, which appeared to single out steam boilers. I agree it would be a project, but I don't see the steam boiler being an issue. And if the "separate water heater" is to have the power of the boiler behind it in making DHW, it seems like it needs to be an indirect, which isn't cheap, and also requires pipe cutting, a circulator, fittings, etc. A freestanding heater undoubtedly would be cheaper, but would almost certainly sacrifice performance relative to a properly-functioning coil or indirect. So hopefully something simple like the cleaning works, because none of the alternatives are clear winners if it doesn't.

Mike

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Post By: Rob R. » Sat. Feb. 17, 2018 12:30 pm

Indirect would be the same job as the plate exchanger, but lots more money.

Oil fired water heater would probably be the simplest solution for lots of capacity and a simple hookup.

Replacing the coil is also an option, but that is not for the faint of heart, or during the heating season.

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Post By: Scottsman » Sat. Feb. 17, 2018 11:24 pm

You got it. 180 is the lower limit. Since I'm using it for my DHW it doesn't go below 180. And the pressurtrol keeps if from going to high. I get 95% of my heat from my stoker upstairs, but with a wife and 7 kids, really like the convenience of hot water off the boiler. I've thought about getting an electric hot water heater, but a new 80 gallon one would be $1,000. Plus I don't have any 220 current going to the basement, and only 100 amp service. Maybe it could be added, but that's going to add up fast. A guy at the store suggested I run vinegar through the coil, so I got a drill pump and was planning on doing that tomorrow. Most of the scale would be inside the coil, not outside, right?

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Post By: Rob R. » Sun. Feb. 18, 2018 7:27 am

Most of the scale would be inside the coil, not outside, right?
Normally yes, but I suppose if your boiler had been poorly maintained for a long time it could have scale/debris on the exterior of the coil as well. Hopefully that is not the case.

Vinegar is not very strong, but it is safe and cheap. Some guys use a small pump in a 5 gallon pail and just let it recirculate through the coil. I think it would also be a good idea to flush it in both directions with full pressure domestic water to help remove any sediment.
Scottsman wrote:
Sat. Feb. 17, 2018 11:24 pm
with a wife and 7 kids, really like the convenience of hot water off the boiler.
That is a pretty serious hot water load.


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