Wiring a thermostat without a C wire

Brianfrench

I have a Taco SR506 relay connectedto a HTP Elite gas boiler. I have 3 zones of heating with hot water baseboard. I have 3 Lennox cooling air handlers in the attic. There are only 5 wires, RH and W go to the Taco relay. It is next to impossible to run an extra C wire through the walls and ceilings. I see there is a SA11 module, however with my system Taco ST506 for heating and Lennox CBX25UVH-024, 2 units and Lennox CBX27UH-030, 1 unit. 
how do I wire the SA11? Is it possible to add a 1,000 ohm 1/2 watt resistor in the Taco SR506, and move the W wire to the C terminal in the, Emerson Sensi Touch Smart Thermostat SKU: R5000.45, thermostats?

HVACNUT

Are you sure theres not another wire that was cut back to the jacket? 
You can't use white as a Common. It's needed to complete the circuit through the thermostat. The resistor goes between C and W in the SR506.
The SA11 looks like it was tailor made for that thermostat. 

GW

You sure you need the G? Swapping g to c is common. We often jump y and g and the ahu if we need to grab a C 

also, if your air handler and boiler are close (can run a wire between the two), you can use the rH and w for ahu wiring now. In this case you set up a small RIB relay to operate the boiler. Small pain but now you have two more wires 

also, Honeywell has their 2 wire with interface module is none of the above suite your fancy 

Brianfrench

HVACNUT said:

Are you sure theres not another wire that was cut back to the jacket? 
You can't use white as a Common. It's needed to complete the circuit through the thermostat. The resistor goes between C and W in the SR506.
The SA11 looks like it was tailor made for that thermostat. 

I pulled out the wires and, yes - only 5 inside the jacket. 

Inside the Taco relay, the R and W terminals connect to the red and white wires respectively. 

There is a 24 volt set of auxiliary terminals in the Taco relay. 

The instructions for the SA11, do not show the Taco application, only gas furnace. 

I did see the Fast-Stat FSCM00, which shows my type of application. 

I am wondering if the SA11 could be wired the same way?
 Thank You Very Much ; Brian 

Brianfrench

Brianfrench said:

HVACNUT said:

Are you sure theres not another wire that was cut back to the jacket? 
You can't use white as a Common. It's needed to complete the circuit through the thermostat. The resistor goes between C and W in the SR506.
The SA11 looks like it was tailor made for that thermostat. 

I pulled out the wires and, yes - only 5 inside the jacket. 

Inside the Taco relay, the R and W terminals connect to the red and white wires respectively. 

There is a 24 volt set of auxiliary terminals in the Taco relay. 

The instructions for the SA11, do not show the Taco application, only gas furnace. 

I did see the Fast-Stat FSCM00, which shows my type of application. 

I am wondering if the SA11 could be wired the same way?
 Thank You Very Much ; Brian 

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Fast-Stat-FSCM00-Install-Instructions.pdf

Brianfrench

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Fast-Stat-FSCM00-Install-Instructions.pdf

The Fast-Stat installation instructions