Tekmar 256 outdoor reset help

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Old 03-08-08, 04:21 PM
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Question Tekmar 256 outdoor reset help

Hi all in an effort to make the boiler better and also run a bit more, by having more than a 15 degree high limit differencial I bout a Tekmar 256.

Having trouble wiring it.

Attached are schematics of the Burnham 206 boiler, and 2 pages of the Tekmar 256 guide.

I'm having problems with terminals 5,6(output boiler) & 7,8 (input boiler demand.

Now, take my boiler as it is now, thermostat is wired to G & R, which if you put a volt meter across you get 24V constant. No problem.

Now, I install the Tekmar, and the Tekmar technical support guy tell me to wire the thermostat to terminal 7 & 9(common)
If you put a meter across 7 & 9 you get 24V constant. So in my mind you have to disconnect both wires from the Honeywell R8285D and attach them to 7 & 9 of the Tekmar, other wise you would have the 24V from the Honeywell and 24V from the Tekmar, if you did it in series off the Honeywell.

Ok then, if you do that what turns the boiler on? The boiler output on the Tekmar, which has no voltage, which gets connected to what???



 
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Old 03-08-08, 06:41 PM
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Take the thermostat off G and R on the boiler.

Wire it to 7 and 9 on the 256

Run a pair of wires from 5 and 6 on the 256
to G and R on the boiler.

In other words, the 256 is wired in between the boiler and the thermostat.

The thermostat tells the 256 there is a heat call.

The 256 fires the boiler ...

But I think yer gonna have to do something with the circulator also ... I'm not so sure the 256 is the correct control for your use...

Your circulator has to run whenever the thermostat calls for heat. When the 256 gets a heat call, it decides whether or not to fire the boiler based on outdoor temp, and boiler water temp. If it decides that the boiler doesn't need to be fired, then the circulator won't be running ...

So, with another relay box the thermostat would wire to that, the circulator would wire to that, and the relay box endswitch terminals would wire to the boiler demand on the 256 .

Like this:

 

Last edited by NJT; 03-08-08 at 07:24 PM.
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Old 03-08-08, 08:46 PM
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Know what else ya need ? a source of 24VAC to power the 256 ... forgot about that ... wonder if you can steal that from the boiler, or if you need another transformer ...

Something else to think about :

You obviously are planning to zone with three circulators ultimately, right ? So, why not rather than wire up the 8845 relay, just go ahead and pick up a Taco zone control panel ? You could install that, rob the 24VAC for the 256 from it, and it also takes care of the circulator relay ... and when you install the other circs and t'stats, ya just wire 'em up ... if you use the 4-channel, you'll have a spare relay ... they plug in ...

Taco SR-504
 
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Old 03-08-08, 09:12 PM
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Old 03-09-08, 09:27 AM
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Originally Posted by xiphias View Post
Xiph, I don't get it ... there's still no circulator control in any of those diagrams ?

Gladiator, don't forget that in order to get any 'useful' reset range from that controller, you NEED to provide boiler protection. If you set it up for say 140 BOILER MIN, your return temps to the boiler would conceivably be down in the condensing range ...

Given that you are now seeing a 20 delta T, you probably don't want the boiler supply to be much less than 155 to keep your return temps not lower than 135 or so ... you MIGHT be able to get by with slightly lower temps being that it's oil fired, but not much...
 
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Old 03-09-08, 12:25 PM
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The TekMar 256 is a straight up ODR control. It goes between the device that calls for heat from the boiler, and the burner controller. Anytime there is a call for heat from a thermostat the 256 also gets that call.

It is then up to the 256 to call for the burner to activate.

The boiler control from the 256 is a set of relay contacts. This is terminals 5 & 6. If there is a set of TT terminals on the boiler controller, they get wired here.

The part I don't understand is the R8285D being used. That is a fan control relay set with 120 VAC input & contact ratings.

From the looks of the data notes, a 24VAC transformer is wired to terminals 8 & 9. This is to provide power for the 256.

And then on the call for heat terminals 7 & 9 get tied together. This is typcially with a relay closure.

Al.
 
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Old 03-09-08, 12:55 PM
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The part I don't understand is the R8285D being used. That is a fan control relay set with 120 VAC input & contact ratings.
There are a few manufacturers that are using this setup on their boilers. They then use discrete sensors to provide limit, roll-out, etc detection and they simply interrupt power to the gas valve.

Honey _calls_ it a fan control, but reality is, it's just a 50VA transformer and an 8882 relay in one package.

I believe the gas valve requires a pretty heavy amount of current from the 24 VAC source, so the choice of that integrated transformer and relay is a 'no brainer' for them... probably cheaper ... I don't know if it's advisable to rob 24VAC from the boiler though... it depends on how much the gas valve actually draws, and how much the 256 draws.

And then on the call for heat terminals 7 & 9 get tied together. This is typcially with a relay closure.
Right... you can also provide a heat call from a switched 24VAC signal if you have one available. You would wire that to 7 and 8 ... (or was it 8 and 9 ?, whatever is in the drawing)
 
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Old 03-09-08, 03:41 PM
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if you are going to have three zones do as trooper suggests and use a Taco SR control but use the SR503 EXP... it is the expandable control ,and then use the Taco PC700...does all the work of the 256 but all you need to do is plug it in to the Taco relay(except for the sensors)..much easier than the 256
 
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Old 03-09-08, 04:31 PM
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Poor, he's already got the 256 though...

The EXP is a good choice for another reason too ... you can add the daughter cards to do pump excercising, indirect post-purge, etc ...
 
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Old 03-09-08, 06:04 PM
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Originally Posted by NJ Trooper View Post
The EXP is a good choice for another reason too ... you can add the daughter cards to do pump excercising, indirect post-purge, etc ...
Downside is that by the time you add all that stuff up, you are probably over the cost of a 256, and closer to a 260, which is a better control than the the PC700....
 
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Old 03-09-08, 06:46 PM
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He'd need a switching relay in any case though, when he goes to 3 zones... so that part is a 'given' ... no ?
 
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Old 03-09-08, 07:24 PM
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yes, but...

PC700 +PC600 +PC605 = ~$330

tekmar 260 = ~$320

And the 260 has more smarts.
 
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Old 03-09-08, 08:51 PM
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Installed the tekmar today. Trooper looks like you were right, circulator does not stay on, even though thermostat is still calling.

Xiphias,
Also a TACO P700 costs about $260, the Tekmar is $139, and can be used with the taco 501 as I understand by taking to Tekmar which makes the P700
 
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Old 03-09-08, 10:26 PM
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Originally Posted by gladiatorxx View Post
...can be used with the taco 501 as I understand by talking to Tekmar
Yes, but why buy the 501 ? single zone relay ... you are planning on going to 3 zones eventually, right ? So, why not go ahead and buy at least a 3 zone relay off the bat ?

By the way, the 8845 relay is basically the same thing as the 501 ...
 
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Old 03-10-08, 09:21 AM
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Yes, thanks, this afternoon I'm going to pick up a SR503.

So would 5 & 6 of the Tekmar go to X1 & ZR of the 503?
 
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Old 03-10-08, 04:58 PM
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Originally Posted by gladiatorxx View Post
So would 5 & 6 of the Tekmar go to X1 & ZR of the 503?
No...

X1 and X2(ZR) on the SR503 would go to 7 and 9 on the 256.
This is your INPUT BOILER DEMAND signal.

5 and 6 on the 256 will be wired to G and R on the boiler.

Set up the jumpers on the 503 for a COLD START boiler ( P to ZC to H )
 
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Old 03-12-08, 11:55 AM
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Ok,

Hooked everything up, might have a wrong hookup. My service switch was left as is, which gives the R8285D power . Then I gave 120V to the SR503, the 256, was getting power from the R8285D 24V constant going to terminals 8 & 9 of the 256.

What I also did which I think is wrong is on the 503 it has 24V, now I'm not sure if this is an input or output. I used it as an output and attached that also to the 256 terminal 8 & 9. I think I'm wiriing that wrong, and either there is no need for 24V from either the 503, or the 8285D to the 256, but not from both places.

Dince I see the boiler with the service switch in the off position actually still runs now.

Also not sure on my feeings with regards to the 256. The supply strap on sensor I located it 5-6 inches right out of the boiler on black pipe. The boiler guages indicates 175-180, but the 256 sensor is off by over 10 degrees so lets say it would read 165 degrees. If it's off that much the ODR is going to give false readings and not wrk properly.
 
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Old 03-12-08, 03:36 PM
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Yeah, right off the bat, if the service switch is still OFF, and the boiler is running, that's a problem ...

OK, I think by having the 24 VAC hooked up to both the 8285 and the 503, you are 'backfeeding' the 24 vac and powering the boiler relay... so, power the 256 from only one or the other.

The 24VAC on the 503 is an OUTPUT. You can use that to power the 256, OR the 8285, but not both.

But I still don't understand how this can happen if you have the service switch OFF.

Check your wiring carefully... make sure that all the devices are indeed wired to the switched side of the service switch.

Don't worry about the temperature difference between the boiler gauge and the strap-on. Make sure the strap on is well insulated. It's not at all unusual for the water leaving the boiler to be cooler than the point inside the boiler that the gauge is reading... and the gauge itself could be 'off' ...

Does the 256 agree with the FLUKE and Thermocouple ? (at the same point on the pipe ? (it was you that had the Fluke dual TC meter, right ? I get confused trying to keep all you guys straight!)
 
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Old 03-12-08, 03:53 PM
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Life would have been so much easier with the Taco SR50X and PC700. Wiring would have so much easier and would not have needed to add anything else.
 
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Old 03-12-08, 04:40 PM
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Yeah, unfortunately he already had the 256 ... oh well ...

gladiator, given the choice, I would rob the 24VAC for the 256 from the 503. The gas valve in your boiler needs quite a bit of current to operate, so I would be leary of adding additional load to that circuit in the 8285 ...
 
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Old 03-12-08, 04:59 PM
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yeah, i could have bought the pc700, but it was almost $300, just for that plus I would need another $120-130 for the
SR503. I got the 256 for $120.

Trooper you say not to worry about the supply sensor, but the settings from the 256 need to take input from the external sensors, so if it's set to manipulate the info from the outdoor sensor, and the reference is 180 degrees, wouldn't the incorrect info from the supply sensor going to the 256 screw it up? Meaning being able to take full advantage of the way it was designed?

Also Tekmar recommended using a thermalwell...hmmm.
 
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Old 03-12-08, 05:18 PM
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I guess I meant not to worry about that 'for now' ...

Get the thing _working_ properly first, then we'll talk about fine tuning stuff ...

A thermowell would of course be more accurate, but it will still work fine as a strap on. Maybe you can think about re-doing the piping when you do the zoning, and add a well at that time.
 
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Old 03-12-08, 05:26 PM
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Does the 256 agree with the FLUKE and Thermocouple ?
rbeck, does the 206 have an adjustable limit switch ?
 
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Old 03-12-08, 06:26 PM
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the 206 , goes up to 220 I think from 150, but only a 15 diff
 
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Old 03-12-08, 06:34 PM
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Looking at some specs on the 4080 limit switch, it appears it may only have an 8 differential...
 
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Old 03-12-08, 06:46 PM
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Does this help at all? It applies to the DHW side of things, but the wiring is for an SR and a tekmar (260). Basically the same deal.

http://s77.photobucket.com/albums/j5...ng_diagram.jpg

I would not be concerned about a difference in temp between the strap-on and the boiler gauge. One or both could be off by a lot. You definitely do not need to put the supply sensor in a well. Wrap it in pipe insulation and call it a day.

Even if these sensors are off by a couple degrees, all it does is force you to come up with a linear shift of your heating curve to account for the offset. Raise or lower the outdoor design temp, or the boil temp at design. It will not affect system performance at all.
 
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Old 03-12-08, 08:10 PM
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tropper I think its a 4080D. You might be right, I'm going to call Burnham in the morning again, I think they had said 15 but i'll confirm.

Did you check out my oher post in the boiler cycle thread with regards to me changing out my pump
 
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