Looking for help setting up a Marathon Logwood add-on

[mpilihp]

Hello all im new to this forum, I wished I had found this site a long time ago. Ive done some reading on it and seen alot of useful information but none that directly speak to what I am trying to do, which is understand how the unit works so I can correctly set it up and get it running.

We bought a used AOB24W which was hooked up but drained and not used for many years as the new owners of the house have a child with a breathing condition. Unit looks great physically, hopefully it is water tight too. Oil is getting outragous to pay for and we have 50 acers of land and now supplement with a wood stove in the basement but want to try and lower the oil use with a wood boiler instead, probabaly wont feel the same but hopefully will feel better on our wallet!

Using the diagram on the marathon website I understand how to plumb the unit up but have questions about the controls and settings.

There are two aqustats on the boiler, one right on the top with the probe going into the tank, and a second one on the top pipe (the diagram calls supply)

http://www.marathonheaterco.com/diagram_addon.html

One Im assuming is to control the loop circulator pump, and the second im assuming is an overtemp control, IE when the temp reaches X activate the bypass zone, or just active a zone valve correct?

My Oil boiler aquastat is set for a low turn on of 170 and a high turn off of 200, dont remember what the diff was, I think 15%.

My questions are this:

Which aquastat should be used to control the circulator pump, the one right on the tank? What temperature shoud it be set to turn the pump on at? My understanding is it should be a temperature slightly higher than the burner on temp (170) so set the circulator to turn on at say 175 degrees?

The second aquastat (on the supply pipe) what is it used for and what temp do I set it to activate at? I think its for the bypass /dump zone but I dont know what temperature to have it turn on at 220??

Next the boiler uses a non-electric automatic draft regulator, guessing its bi-metal unit of some sort. It has a long arm with a chain connecting it to the draft door at the bottom. Mine reguardless of where I turn the temp nob has the arm down and the draft door closed. Im assuming with no fire in it the arm should be all the way up and the chain adjusted so the draft door is wide open, then as a fire inside heats it up the arm would lower and close the door correct? I see a set screw on the backside of the arm, can I just loosen that and set the arm up when its cold and retighten it to set it up correctly?

Ive read on this site that Marathon says no chimney draft control is needed but someone stated they put one in to assist in regulating the fire for longer burns, I was thinking it would be wise to have one just for safty sake in case it was a run away fire.

What temperature should I run the boiler at? THere is a nice temp gauge on the unit im guessing its important to run it at a correct temperature.

Lastly does anyone have the manual for the Logwood add-on boiler? Could someone email me a scanned copy of them?

Your help wll be much appreciated!!

~ Phil

 

[Eric Johnson]

Welcome to the Boiler Room, Phil. I had one of those for 9 years (the Model 24) and I can probably answer some or all of your questions when I get time. Right now, I've got a dentist appointment.

BTW, you can probably get a manual from the mfg. They're still in business and still making that boiler.

 

[Eric Johnson]

OK, I'm back.

If your Logwood boiler doesn't have the oil burner option, then the second stat is probably an overheat control. If it has (or had) an oil burner, that's the oil burner overheat shut-off stat.

I'd use the one in the well in the boiler to activate your circulator.

You are correct on how the bimetal (Ammark?) draft control works. When the boiler is up to temp, it should be fully closed, gradually opening as the boiler cools off. High tech approach to adjusting it: shorten or lengthen the chain.

The mfg. recommends running at temps above 200. I think it might be 220. I did that for years, but it's living on the edge. The theory is that high temps will facilitate secondary burn and cut creosote production. I doubt it did either for me. Sometimes I would get a lot of creosote, and sometimes not much. Just don't try running it at 140 or thereabouts. Then you've got a real creosote factory.

I'd consider putting some sort of low return water temp corrosion protection in that boiler. Mine failed after 12 years, probably because I didn't. What you want to do is figure out a way to redirect some of your supply water into the return to keep it above 140 as much as possible. Cooler temps at the return will create condensation in the firebox and lead to corrosion (from the inside). Don't ask me how or why, but it's an established fact.

 

[mpilihp]

Hi Eric thanks, I took a closer look at how the aquastats are wired up and the one on the drum has its to close output contacts connected to the 120v feed to the circulator pump (yes the pump is still wired to it), its activation temp was 220 degreese.

The second aquastat on the Supply pipe has its 'close' contacts just bell thermostat wire which im assuming went to a controller to turn on a pump for a dump zone, its activation temp was 220 deg which makes sense. If the boiler gets too hot and pressure is building dump the heat to a zone...

Im guessing the temp on the circulator pump is too low, my oil boiler burner controller is set to turn on at 170 deg so I would think the wood boiler cir pump should not turn on until say 172-5 or so, right?

As for the condensation thing, the Marathon rep said they didnt have rust corrosion problems because it was a pressurized vessel but what your saying is when the cooled water comes back into the boiler it causes condensation huh? Their diagram shows the return inlet is on the bottom and the supply(out) is the one on the top correct?

Thanks for the advise Eric.

~ Phil