View Full Version : Boiler Wiring (Weil CGa, Tekmar 256, Taco SR501, and T-Stat)

10-15-2007, 05:44 AM
I have:
new WeilMClain CGa standing pilot boiler.
two (2) 007 Taco circulators (supply & return sides)
a Taco Single Zone Switching Relay (SR501) for 2nd circulator
Tekmar 256 single stage boiler control
Thermostat (boiler demand???)
one (1) 24v transformer

I just can't seem to get the wiring concept down. The boiler has 2 wires labled Thermostat.


Any thoughts? Thanks.

10-15-2007, 07:08 AM
Oh boy. It seems to me that we've gotta go a little carefully here.

Let's start with your proposed layout. Draw your own schematic based on your current understanding. Maybe some questions from us will help you think it through.

How many zones do you have? (All thermostats will tie into the boiler's thermostat circuit to provide the call for heat.)

What load will the circulator circuit handle? You may be able to run both taco's off the boiler power if it's up around 4 amps or so. Otherwise you'll need to use the relay on the crculator circuit.

What boiler controls are in place and what are you adding? The schematic shows where the added controls should be in the circuit so all you need to do is identify the additions and the appropriate wires.

You'll have to supply power to the boiler and circulator relay (if used).

Draw your schematic with notes on wire colors and identify control or function. Reference your wires to the manufacture's schematic so function and location are clear to you. Write your questions right on the schematic.
Take your time and think it through based on function.

10-15-2007, 09:11 AM
I have 1 zone.

Not sure what the circulator circuit can handle???? How can I find out? Each pump is @ 0.7 amps.

Where in the schematic do you see where the added controls should be?

10-15-2007, 12:28 PM
I've gotta say oops. I just looked up the Tekmar 256 and it's an outdoor reset. I can't help much with that. What I do see is the Tekmar boiler taps will tie to the thermostat circuit on the boiler. You'll need to supply 24 VAC to the Tekmar, maybe that can be tapped from the R and C terminals on the boiler. Make sure you aren't overloading that transformer.

I suspect you won't be able to run the circulators from the boiler power circuit, e.g. the relay will be required. That relay will have to be on the circuit with the thermostat so the circulators will run regardless of whether the boiler sees a call for heat or not. The result will be along the lines of: the wall thermostat will make a call for heat which results in the circulators starting and the Tekmar sensing the call for heat. The Tekmar will check the water temperature and decide if the boiler needs to see the call for heat. The Tekmar will make calls for heat to the boiler as needed to maintain the water temperature that it desires.

Like I said. Draw your schematic and post it. Label all taps and note function. Expect corrections, it's no big deal if it takes two or three trys to figure it out.

10-16-2007, 08:08 AM

10-16-2007, 09:14 AM
Ok, now we've got something to work with. It looks like you've diagrammed things clearly.

With the proposed diagram water won't circulate until the Tekmar calls for heat. The Tekmar call for heat depends on the thermostat calling for heat and a water temperature below the Tekmar's target. In other words the circulator and boiler will shut down when the water reaches the Tekmar set point even though the thermostat is still calling for heat.

I think that you want water to circulate any time a thermostat calls for heat. That means that the relay has to go in the thermostat circuit.

The Tekmar control will tell the boiler when to add heat to the system (maintain water temperature) so the Tekmar has to control the boiler. The boiler shouldn't be connected to the relay.

That's my $0.02.

10-16-2007, 10:13 AM
Why circulate without heat?

Many thanks!

10-16-2007, 10:32 AM
As I understand it, the system circulates without constantly adding heat to operate the system at a temperature lower than design.

When it's only cool outdoors and not cold then the system doesn't need to provide as much heat and can operate at a lower water temperature, say 140 degrees instead of 180 degrees. The Tekmar control will cycle the burner on and off to maintain about 140 degrees while circulation continues and provides gentle and fairly constant heat in the house.

If the reduced temperature mode of operation is not desired then the Tekmar control is not necessary.

10-16-2007, 10:49 AM
So what triggers the SR501 relay to power the 2nd pump?

10-16-2007, 10:56 AM

As long as everything is set up and specified correctly then closing the thermostat circuit will trip the relay. That said, I'm not an electrician and still operate with a "magic smoke" understanding of all things electrical.:D

You'll want the relay to run both circulators (I think).

10-16-2007, 04:26 PM
You want the circuilators to be controlled by the thermostat. The reset control keeps the available water within spec based on the load (outside temp).

10-18-2007, 01:04 PM
OK, so i have both circulators on the single relay with the TT wires on the relay goin got boiler. I'm still lost as to where/how to wire in the Tekmar 256?

see: http://www.xjmllc.com/images/im4510_20071018_145844.pdf

10-19-2007, 07:22 AM
Here's my suggestion for wiring from thermostat to relay to tekmar to boiler. I've ignored the other sensors on the tekmar.

10-26-2007, 05:09 AM
Thanks for everyone's help. I'll post final diagram shortly.:D


03-09-2008, 09:31 AM
I realize this is an older thread, but there was never any real resolution given, so for the benefit of future readers...

Room thermostat wires to the thermostat terminals on the SR501.

The T T terminals on the SR501 wire to 7 and 9 on the Tek256.

The 5 and 6 terminals on the 256 wire to the G and R on the boiler.

In this way, the circulators run on a heat call, the TT signal tells the 256 that there is a boiler demand, the 256 evaluates the water temp in the boiler and the outdoor temp and determines whether it's appropriate to fire the boiler.

10-22-2008, 07:10 AM
I still have not performed the wiring, but I will be THIS week. I will post final results shortly after.

Again, thanks to all and sorry for the delay.


10-22-2008, 11:16 AM
Troopers last post is correct. You can get all the proper wiring diagrams from Tekmar or from Taco. Tekmar makes the controller for Taco.

11-14-2008, 06:56 AM
My situation is similar. My current setup is Honeywell R8182D running oil burner in a Utica cast iron boiler for radiant heating only, no DHW. I wish to add a Tekmar 256 for outdoor reset control. [I live in Boston area]. I want to keep the 8182, but can't figure out how to wire the circ. pump so that it starts when thermostat calls for heat, while the Tekmar 256 controls oil burner start/stop based upon thermostat and outdoor temp.
I appears that I should add a SR501 switching relay. Is that correct? Is there a better way to accomplish my objective?

Note: there are 3 zones, with Taco 24 volt zone valves, so I must be sure at least one zone is calling for heat before activating the single circ. pump.

Here is link to Honeywell R8182D, installation instructions are at bottom of page:

11-14-2008, 01:12 PM
Pull and cap the blue wire that goes to the low limit side of the reverse aquastat. Circ will run and boiler will cold start.

11-28-2008, 08:41 AM
My Honeywell R8182D, has 2 blue wires that plug in by the Differential Setting Dial. Do I 'unplug' both blue wires and tape them up, but NOT connected to each other.

I presume the only operational change will be that the circ pump runs WHENEVER the thermostat calls for heat. True?


11-28-2008, 03:54 PM
you only need to remove and cap one of them. The one directly below the low limit dial.

11-30-2008, 12:45 PM
Thanks! What a great forum this is! Great members too; no rambling.