Tekmar 256 and Weil-McLain CGi-8 wiring

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Old 12-11-10, 12:11 PM
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Tekmar 256 and Weil-McLain CGi-8 wiring

I have a Weil-McLain Gold CGi-8-PIN boiler and am having trouble figuring out the wiring to add a Tekmar 256. I know from reading other posts that the thermostat needs to control the circulator, and the 256 the boiler, but don't know where to tap in to supply the 256's boiler contact (5,6) and boiler demand (7,9) connections.

I've seen some nice 256 wiring diagrams from Trooper, but they didn't seem to cover the CGi.

The wiring diagram for the CGI-Series 2 wiring diagram is here:
Wiring Diagram

Thanks much!
 
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Old 12-11-10, 03:33 PM
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George, do you have multiple zones in your home with electric zone valves?
 
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Old 12-11-10, 05:17 PM
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The CGi isn't an easy one because of the fact that it's all wired with Molex connectors.

My goal would be to disturb as little of the original wiring as possible.

You need 24VAC to power the 256, so that has to come from somewhere. In the interest of not 'cutting into' the CGi wiring, I would opt for an external 24VAC transformer.

If you wired 5 & 6 as an 'additional limit' as shown on the CGi schematic, and LEFT THE CIRCULATOR WIRED AS-IS, you could add something like a Honeywell R8845 relay to the system to provide the 24VAC for the 256, AND provide the interface for the thermostat.

Using the 8845 might seem like 'overkill', but since it nails a couple birds with one stone, it might be the simplest and most cost effective solution.

R8845U1003 - Honeywell R8845U1003 - Universal Switching Relay w/ Internal Transformer

So, let me know if you've got multiple zones, because that might complicate the plan.
 
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Old 12-11-10, 08:27 PM
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Trooper:

This is a 1924 house with hot water radiators, so no zones or electric zone valves. Boiler is in basement, thermostat is on 2nd floor and also controls separate forced air AC in the attic, which provides power for thermostat.

I already cut into the existing wiring to take the 24VAC for the 256 from the transformer for the CGi, figuring it didn't need much power -- I do have a spare 24VAC transformer if that would be better.
 
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Old 12-11-10, 08:45 PM
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Problem is that you will still need a relay... there are a few ways to do this, but all of them need the relay.

Here's a drawing of what I feel is the easiest and most cost effective. The 8845 is under $50. I don't think you can get an individual relay, socket, enclosure, wire, lugs, transformer, etc etc... for that $$.

I hope this is readable... it's gonna probably rescale smaller for the forum. If you have trouble let me know and I'll figure something out.



If you go right to the photobucket page here:

George.jpg picture by JeffPicks - Photobucket

You should be able to see it better.
 
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Old 12-12-10, 12:26 PM
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Thanks for the good diagram, it displayed fine and looks pretty straightforward. I'll let you know how it works once the R8845 arrives.
 
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