High Limit on Boiler Question

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MxAnt228
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Post Thu. Nov. 22, 2012 8:16 pm

Currently have a Marathon coal/wood boiler tied into my oil boiler with a relay set up that If my fire goes out / drops below 90 it fires the oil boiler. However when my oil boiler fires it heats up to the 200 degree high limit, it shuts off and kicks back on the coal boiler circulator instead of the oil causing it to pump 90 degree water around being useless. Anyone know of how I can change it to power the oil boiler pump instead of the coal when it reaches high limit?

Thanks Anthony

Ops164
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Posts: 34
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Stove/Furnace Make: Harmon
Stove/Furnace Model: Mk III
Location: Central PA

Post Sun. Nov. 25, 2012 5:20 pm

There is no reason that one pump can't be used to pump thru both boilers. First thru the coal unit, then the oil burner. This will also keep both boilers warm and prevent condensation in the flues.

I'm not sure, by your description, what is going on here. If each boiler has its own pump, why isn't the pump for oil system running?

Ops

MxAnt228
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Post Sun. Nov. 25, 2012 9:06 pm

I have a main loop with a supply and return line for each the coal and oil boiler and have a pump for each. The heating system is radiant with a secondary loop also. Everything is working fine except when the oil boiler reaches the high limit 200 degrees, it shuts off the burner and oil boiler pump and energizes the coal boiler pump, no idea why and how it is getting energized, when it should be off and oil boiler pump should run til it reaches its differential 10 degrees.....Sorry for lack of information


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lsayre
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Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Blaschak Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75
Location: N/E Ohio, between Medina and Wadsworth

Post Sun. Nov. 25, 2012 9:16 pm

Perhaps at the same time that the oil boiler is hitting its high limit the coal boiler is seeing the same 200 degree water temp and activating its dump zone. That would turn on the coal boilers pump.

Ops164
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Posts: 34
Joined: Fri. Jan. 13, 2012 9:04 pm
Stove/Furnace Make: Harmon
Stove/Furnace Model: Mk III
Location: Central PA

Post Sun. Nov. 25, 2012 10:03 pm

Your oil boiler is miswired. Your high limit should only cut off the burner, not the circ.

This isn't something that I can tell you how to do over the internet. The chances of miswiring something and creating a hazard are too great. You'll need someone local to rewire it for you, and don't call an electrician. you'll need someone who knows how a boiler should be wired in the first place, which the last guy who worked on it didn't..

Ops

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