Questions About Wiring a Tekmar 256 to a Utica MGB Boiler

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Old 03-19-12, 07:22 AM
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Question Questions About Wiring a Tekmar 256 to a Utica MGB Boiler

Hi DIYers.

I'm getting ready to embark on my first boiler job. All of my material is in my basement but before I start ripping out, I have a question about wiring a tekmar 256 OR to a Utica MGB boiler with intermittent ignition.

I've poured over the OEM manuals, looked through the forums and the only part of it I'm scratching my head about is what to do the terminal 7 - the 'input boiler demand signal' terminal - on the tekmar.

I'm setting up a simple 3 zone system with Taco zone valves and relay (a ZVC403-2), 1 circ pump on the boiler, and no priority or HW. My wiring plan is to take the 24 VAc for the tekmar directly from the transformer in the ZV relay box, and break B1 going to my gas valve thru terminals 5 & 6 on the tekmar (thanks to the jaguar79 thread in this forum). My gas valve's anticipator setting is 0.5 amps so I'm expecting its peak draw to be well below the 5.0 amps that terminals 5 & 6 on the tekmar can handle.

So, for terminal 7 on the tekmar, do I leave it empty, jump it to terminal 9 on the tekmar, jump it to one of the T-T terminals coming from my zone relay box, add an additional relay to the valve end switches (that seems a little unnecessary) or something else? I'm thinking I need to do nothing with it and if so, could I expect the tekmar to open and close 5 & 6 and fire the ignition based on the outdoor setting or do I need to close 7 & 9 continuously? Can't post pix so the link to the tekmar documentation is:

Boiler Control 256

Thanks in advance for any advice you can offer.
 
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Old 03-19-12, 09:12 AM
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Hi Jeff, you've got a few misconceptions I think... your application should not have to wire in series with the B1 terminal on the control...

Can you place a link to the thread which you saw this in for context?

I'll help you with this later... this evening.
 
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Old 03-19-12, 10:00 AM
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Thanks Trooper. I was referring to the conversation that starts at post #3 in the following thread:

http://www.doityourself.com/forum/bo...irculator.html

Honestly, it made sense to me. Looking at my boiler wiring diagram (page 17 here: http://www.ecrinternational.com/secu...ument/2490.pdf), B1 contains the two in-line GV safeties and comes from the electric vent damper relay. I thought having the tekmar break that once it sensed the temp it was looking for, it would prohibit the GV from firing but still allow the circ pump to run, no?
 
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Old 03-19-12, 04:22 PM
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Let me ask another question or two...

You say you're setting up 3 zones with a 403 panel. This means that the home was all one zone before and the thermostat was wired directly to the boiler?

You have a couple choices:

1. You could remove the circulator from the boiler and wire it up to the auxiliary relay on the Taco panel. This way the 256 could wire between the 403 endswitch and the Utica T T terminals.

2. You can leave the pump where it is, and as the other thread stated, wire the 256 in the B1 circuit. This brings up the question of what to do with terminal 7. You MUST do something with it, else the burner will never fire. Jumpering it to terminal 9 might be the answer...

Let's think about this...

When one or more t'stats call for heat, the 403 endswitch wired to the T T terminals of the boiler will signal that there is a heat call. With the 256 strapped on 7 and 9 for a constant demand, if the boiler is cooler than the 256 target temp, the burner will fire. The circ will be running. If the heat call continues, and the boiler reaches the target, the 256 will shut down the burners.

Sounds good...

I had been thinking for a while that you would need to use the aux relay on the 403 to send a demand to terminal 7 on the 256 at the same time that the endswitch fires the boiler, but I don't think that's necessary... just extra wiring. It would work, but keep it simple.

I believe you could also 'rob' the power for the 256 from the Utica aquastat, but getting it from the 403 is also fine.

I think we have a plan, unless someone else finds a flaw in the logic...
 
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Old 03-19-12, 06:07 PM
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Thanks again Trooper.

Right now the house is wired as 2 zones - the main house and an addition. Two circ pumps on a 30+ year old peerless oil boiler with a gas conversion unit that we inherited when we bought 10 years ago. It's just time to upgrade

When I land the new boiler, I'm going to make the master bedroom a third zone. I'm in a 1.5 story bungaloo so the entire upstairs as the master suite.

I see it the same way I think you do. Take the OR out of the equation for a moment and I'd wire the 403 relay like you described - regardless of which zone called for heat, one TT signal to the aquastat from the 403, the boiler would fire and the zone valves would respond accordingly.

I think the simplest way to add the OR to the mix is to have it interface directly with the gas valve up stream of its in-line safeties. I got the idea after a buddy with a Utica mentioned in an unrelated conversation that he has his auto damper wired open to ensure his boiler fires. He warned me that during the install the sheet metal damper housing is so flimsy that the slightest 'nudging' into position could put it out of round just enough to cause the butterfly to stick while trying to open which prevents the relay to the gas valve from closing.

I'm guessing initially I'll have to put a jumper between 7 and 9.

My boiler is arriving on a truck tomorrow and the weather forecast for SE PA will allow me to take my time with it. I'll be sure to check back in, likely early next week, and let you know the results.

Thanks again for responding!
 
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Old 03-19-12, 06:18 PM
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Cool... show us some pics as you go. Easiest IMO is a free account at Image hosting, free photo sharing & video sharing at Photobucket, upload pics there, come back here and drop a link to your PUBLIC album for us to browse.
 
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Old 03-30-12, 12:18 PM
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Okay Trooper. As promised, i'm back with a report and a link to some pix. My boiler install is complete, the Tekmar 256 is up and running, and in general I'm really pleased with what I'm seeing. I've uploaded a few pix from the install here:

https://picasaweb.google.com/1149388...eat=directlink

Please note that I've added a lot of commentary to the picture captions so if you're really looking at this thread and considering a 256 for yourself, be sure to look them over. There might be a few hidden tips in there worth noting.

In general, I'm really happy with how the job went overall and how I think the 256 is performing. I say "I think" because it's been unseasonably warm here in the Philly burbs the past few weeks and the boiler hasn't been running too too much. What I've noticed immediately is that when the boiler does fire, the 256 seems to do a good job of controlling "overshoot". Rooms and radiators aren't really heating up excessively. Before the new boiler, when the the t-stat would call for heat and the boiler would fire, I was heating a lot of cast iron with water at 180. Now, with cooler water (between 140 and 180 depending on the outside temp) flowing through the system I'm not really noticing the heat cycling. In fact, I'm not noticing the heat running which to me is a real positive thing. Still tweaking settings and experimenting with hi and low limits but so far - good stuff.

As far as the install goes, I was able to wire it as we discussed below. Breaking the B1 feed and integrating the 256 to the boiler system there was simple and effective. The pix captions explain in more detail but like it's discussed below, doing it this way allows the ZV controller to control the boiler (circ pump, auto damper, etc) sort of in parallel with the 256 controlling when the gas valve fires. Works Perfectly!

Have a look and let me know if you have any quesitons. Thanks for your input.
 
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