installing Tekmar 256 to a weil mclain cg5PI boiler

T0nesea

Thanks in advance, Im a homeowner trying to install the 256 to my boiler, its a single zone unit,

slots 1-4 are straight forward and complete, slot 9 also is good with 24v.

Now with 5,6,7,8 I'm have a tough time where these need to connect.

5&6 boiler control ? is that the circ pump relay?

7-T ?? for thermostat? one diagram shows it connected to 9?

8 is r+ is that also from thermostat

any insight would be helpful, my big issue is terminology of parts

I cant get thru to anybody online

Tonesea

EdTheHeaterMan

I just helped someone with this yesterday. they also had a Weil McLain (but it was steam)

Give a minute to look for that wiring diagram

EdTheHeaterMan

If you have an indirect water heater, then there are some more wires to connect.

If you have an indirect for DHW, is it controlled by a zone valve or by a separate circulator?

T0nesea

Hi Ed, this unit is different than my 256, if the boiler connects are the same where am i connecting from 256 to where on boiler?

EdTheHeaterMan

OOPS. that is a 260 not a 256. Sorry

Let me look into the 256 for you.

EdTheHeaterMan

OK here is the diagram and there is one thing that gets most folks confused.

The C from the transformer needs to be connected to both the R on the thermostat and the C- on the Tekmar for this control to work. I don't know why, it just is.

And that makes it very confusing when you need to connect a smart thermostat that requires a C terminal for the thermostat because the ends up connecting to the R on the transformer.

T0nesea

Thank you!…1 more question your showing the "boiler output as T/T at the boiler…what does T/T stand for ?

quick note this whole Tekmar thing started when I upgraded to a "smart" therm!! lol

Thank you