Help with Tekmar 256!

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Old 10-14-19, 02:27 PM
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Help with Tekmar 256!

Hello all,
This is my first post but have been reading this site for sometime...

I am in the process of installing a Tekmar 256 control onto my 1970's Weil-McLain boiler. I have hooked up all of the inside and outside sensors and have given the controller the 24v from the transformer. The area that I am confused by is that my current boiler has a thermostat on it that I can set to the max temperature ( Maybe called a Aquastat but not sure), am i suppose to bypass this unit?

Currently I have taken the red and white wires that were hooked up inside the boiler and moved them to the Tekmar ( 7 and 9 ) and have run a new set of wires from the Tekmar ( 5 and 6) back to where the original power demand was from the zone valve. With this done my aquastat is still hooked up. Does this seem correct? I cant find a wire diagram that is showing hooking up the Tekmar with a existing aquatsat.

I have attached a picture of the inside of my boiler. The black box onto is the thermostat I am talking about and the red and white wires are from the Tekmar.

Any help will be appreciated! Thanks!
 
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Old 10-14-19, 04:50 PM
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Hi, what is the model # of the WR control? That black box maybe a Hi limit control, is there a circulator on this system?
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Old 10-15-19, 09:14 PM
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Aquastats and other controls often use the words “high limit” for what is temperature setting.

The Tekmar 256 is an aquastat to control, set or limit boiler temperate.

The label “out door reset” is confusing. But then many products called aquastats are often multifunction and add further to the problem.

The original aquastat wires should be connected to the Tekmar 256.

Zone valves should be activated by room thermostats not ODR's
 
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Old 10-18-19, 08:16 PM
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When I installed a Tekmar a few years back, I was advised to keep the aquastat in the circuit and raise the aquastat high limit setting to something above the Tekmar's high limit setting....that way, the aquastat will still function as a high limit "safety" in the event the Tekmar fails to shut off the burner (for whatever reason).
 
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Old 10-19-19, 09:22 AM
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Bad idea to keep both old aquastat and Tekmar in circuit.

Tekmar is very accurate with 1 degree F delta-T.

Old bulb type aqustats had very crude settings. Delta-T more likely 10, 15 or 20F. With both aqustats in circuit some weird things could happen.

My old fired cast iron boiler overshoots setting 10F. So set Tekmar limit to 170F which provides actual 180F top.

Use separate PID temperature control as over temp limit set at 190F. A second PID channel is used to turn off circulator when return water is below 135F
 
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Old 10-20-19, 04:51 PM
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I've had the aquastat in the loop acting as a 2nd high limit safety for several years now, and there hasn't been any issues. I have it set at 210*F (same temp. setting as the code-mandated manual reset HL safety that is also on the system).

The aquastat is an older Honeywell L4062B with a fixed 5 degree HL differential ....which is a big reason why I decided to add the Tekmar unit, so that I could have more control over the HL differential.

The Tekmar 260 has a BOIL MAX setting which is the highest water temperature that the control is allowed to calculate as the BOIL TARGET; I have it set at 185*. So even taking into account any sort of overshoot or "heat soak", the aquastat does not interfere with the normal operation of the Tekmar.

In my application, keeping the aquastat in the circuit works out fine.
 
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Old 10-21-19, 10:26 AM
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Rockledge might want to verify settings on those controls. A reliable over temp shut off is important for safety.

Even when new their calibration is poor and unreliable. The sensing bulbs leak over time and things get way off. Modern electronic sensing is more accurate and reliable.

A good way to confirm settings is with $16 recording, dual probe digital thermometer:
https://www.ebay.com/itm/6802-II-Dua...Jvs2Xo3KWm9k6g

Also a stainless probe is good way to measure stack temperature to monitor boiler efficiency.

https://www.ebay.com/itm/2m-Stainles....c100005.m1851
 
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