Harmon SF160 Replacement controls

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Bill72Bill
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Hand Fed Coal Boiler: Harmon SF160

Post Mon. Nov. 27, 2017 3:32 pm

Hello everyone. New here. I’ve enjoyed reading many posts with great information.
I’m here trying to help my father with his boiler controls. He purchased the Harmon new about 15 years ago. The boiler itself is excellent. The controls have been an issue as it nearly boiled over in the past after operating fine for over 10 years. Now he is concerned it may happen again and constantly checks.....
He was never quite comfortable with the control setup & would like to replace with a “simple” setup. There is nothing fancy here. Single zone system.

I need an aquastat that will turn the circulator on and off along with opening & closing the draft door at the prescribed temperature ranges. No digital needed. The old school dials will be just fine.
Another question is the depth of the temperature probe well. If anyone knows what depth probe will fit would be helpful.
Thanks in advance for your time & help.

lzaharis
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Post Mon. Nov. 27, 2017 5:49 pm

HelloB72Bill,

On my old Switzer hand fed wood and coal boiler the builder used a Dayton shutter motor mount that that had a coil spring to return it to the bottom(closed position for the two damper doors that was wired into the thermostat controls to activate the shutter motor when the boiler was at the low limit or below to add more air to the fire and shut the shutter motor off when the high limit was satisfied. It was the same type of set up for exhaust fan shutters.

The mechanical Honeywell L8124L1011 which I have for my keystoker works very well. All you need to do is purchase the proper Honeywell probe well and be sure not to put any pipe dope on the threads of the probe well as it affects the conductivity of the probe well.
I always left my hand fed at summer temperatures when burning and I am also using summer temperatures with my keystoker KAA-4-1 as well.
Does your father use the Harmon firebox reducer? Are you also using the single loop for the dump zone as I am with mine??? Do you have an exisiting honeywell L6006A in the steam chest??

Bill72Bill
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Hand Fed Coal Boiler: Harmon SF160

Post Mon. Nov. 27, 2017 7:43 pm

Thanks for your reply. I guess I should mention that the original controls are Johnson controls.(A350) It is a 3 box system. The Harmon has a small motor to open & close the draft door already. I believe it to be 24v.

The piping is all on one loop so guess a "single" loop. No firebox reducer was ever needed here in Pennsylvania.

Simply, what I believe is needed is a setup that turns the water circulator on and off and opens & closes the draft door all at prescribed temps.

lzaharis
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Stoker Coal Boiler: Keystoker KAA-4-1 dual fuel boiler
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Post Mon. Nov. 27, 2017 11:30 pm

You can not do it that way safely and it will not be up to code.
You need the triple aquastat. That is what was set up with your harman with the three sets of johnson controls aquastats with three probes and three wells.

The AHS folks are now the owners of the Harmon brand. It would pay you to call AHS and ask if the three controls are still available as they control the high and low limit and the dump zone as well as the shutter motor using the high limit aquastat.


Otherwise you need a mechanical triple aquastat and a separate L6006A for the dump zone control and they both have to have the correct probe well that matches their probe length.

Bill72Bill
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Hand Fed Coal Boiler: Harmon SF160

Post Mon. Nov. 27, 2017 11:48 pm

Thanks again for your help BUT the Johnson controls only use 1 well & 1 probe total. As far as the company goes(Harmon), they built a good boiler but always want to hand you off to a local distributer. Not very helpful on there behalf.


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BlackBetty06
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Hand Fed Coal Stove: Hitzer 50-93
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Post Thu. Nov. 30, 2017 12:16 am

If im understanding correctly what you say you need, You can use a plain jane honeywell aquastat. Wire the pump through the contacts that close on temperature fall and open on temperature rise. Then hook up an isolation relay with a 120 volt coil. Energize the 120v relay coil with the contacts on the aquastat when the pump kicks on. Then wire your draft motor through the normally open contacts of the relay. So boiler temp drops, pump kicks on, relay energizes and powers draft motor. Done. However that seems too simple. Ive never ran a coal fired boiler but i know its not like oil or gas that when the call for heat stops, the fire is gone. I would imagine you will need to keep your circulator running while the fire dies down gradually, otherwise your gonna boil and blow off the relief.

Bill72Bill
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Hand Fed Coal Boiler: Harmon SF160

Post Thu. Nov. 30, 2017 2:21 pm

I'm thinking I can use 2 separate aquastats. One to break on rise to operate the draft door & one to break on fall to operate the circulator. This way I would be able to precisely control the temp. range.
Again, this is a simple single zone system. There are NO thermostats hooked up. I just want to turn the circulator on and off at prescribed temps. On at about 170, off at about 140 give or take.
Then the draft door open at 120 or so & close at 160-170....
Does this make sense to you ?

Thanks everyone for your input.

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McGiever
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Post Thu. Nov. 30, 2017 5:06 pm

Yes, it basically will work, but lacks a important safety feature.

If your damper door were to electrically not stop or not close when water temp setting signaled it to close you would have a runaway fire with no backup to step in and force it closed...this is a catastrophic event for any solid fueled appliance.

There should always be a "Fail Safe" wired into the circuit.
A "Fail Safe" or "High/High Limit" that does NOT do the everyday cycles for controlling but is there waiting "Solely Just In Case" the other one "Fails".

Do you not run a "DUMP Zone"?

A DUMP Zone Aquastat , when used, can double as the "High/High Limit" .

Anyways, adding a 3rd aquastat, with both a N/O and a N/C contact, would get you both a H/HL and a Dump Zone trigger. :)

To me, it is strange to not use any thermostat. :baby:

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BlackBetty06
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Stove/Furnace Model: 50-93
Location: Lancaster county PA

Post Thu. Nov. 30, 2017 8:22 pm

Yea how could I forget that. Honeywell makes a manual reset high limit switch that could be wired in series to the operating control. Are the draft motors on these boilers power open spring return or power open and close? You could also put a high limit in the stack and wire that in also. But at this point before you re engineer the wheel I would give legacy a call and see if they have the oem stuff available or get the part numbers off yours and try to source it locally

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Rob R.
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Post Thu. Nov. 30, 2017 9:03 pm

If the boiler has two 3/4" or 1/2" tappings I would just install Honeywell single aquastats with the recommended well. An L4006A would work well for controlling the draft door, and a L4006B would work well for a dump zone aquastat.

Do yourself a favor and wire up a thermostat and a relay to control the circulator.

http://www.supplyhouse.com/Honeywell-L4006A2007-H ... -5481000-p
http://www.supplyhouse.com/Honeywell-L4006B1163-C ... -3873000-p
http://www.supplyhouse.com/Argo-AR822II-1-Zone-Sw ... hing-Relay


Bill72Bill
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Hand Fed Coal Boiler: Harmon SF160

Post Thu. Nov. 30, 2017 9:21 pm

Thanks again for the replies. The reason for No thermostat is that it is a ranch style single floor house with only one zone. There is a DS stove on the living level that is commonly used all fall & winter long as a secondary heat source. The thermostat will never call for heat(or hardly ever) because of the second stove. Boy, does he love that DS stove. It may use a bucket of coal every 2 days or so just going easy & 3/4-1 bucket a day when it is real cold out.

The dump zone would be the regular zone. Only 1 zone threw the whole system.

The boiler draft door is electric open & close.

He is NOT wanting to use the Johnson controls again as he fears they will fail again. Ideally, he would prefer to go ALL non electric BUT that is not really an option with an electric circulator.....

Either 2 aquastats as described earlier OR 1 aquastat that will run the circulator AND a Sampson valve (if that is the correct term) to hook on the draft door & disconnect the electric motor from the draft door.....

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Rob R.
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Post Thu. Nov. 30, 2017 9:22 pm

The Samson aquastats work very well.

Bill72Bill
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Hand Fed Coal Boiler: Harmon SF160

Post Thu. Nov. 30, 2017 9:43 pm

There are (2) 3/4" taps for probes. One on each side of the front. I could use the one on the left for the circulator aquastat & the one on the right for the draft door( either electric or Sampson aquastat). Does that make sense?

Rob, I'm obviously not a pro at this in any words. I wasn't sure why I would need any type of relay? If I ran both of the aquastats independent of each other. Thanks again.

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Rob R.
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Location: Chazy, NY

Post Thu. Nov. 30, 2017 9:45 pm

The relay would allow the use of a std. 24 volt thermostat.

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