question on T-stat w/remote sensor wiring

[Mikepier]

I have a White Rodgers T-stat in a multi-family home that I'm trying to hook up a remote temp sensor. I have a basic steam boiler with the connections to the T-stat as shown on the top of page 4

I tried hooking up the remote sensor, I followed the instructions of cutting a jumper on the T-stat and also setting the programming to "sensor on", but it still does not read the sensor. One thing it mentions in the manual is that the sensor needs constant 24v and that I might need an "isolation relay" on power stealing t-stats as shown on the bottom of page 2: this confuses me. I thought that I do have 24v coming from the boiler Xfrmr. Is this isolation relay necessary? And is the Xfrmr they show on page 2, is this a seperate Xfmr from the one on the boiler?

[Nate Certified Heating and Air]

You may or may not have 24v coming from the boiler tx to the stat. A power stealing thermostat has the following wiring Red(24v), White(Heat), Yellow(AC), Green(Indoor Blower) Blue(24v Common). A non power stealing thermostat will have all the same wires EXCEPT the Blue common. The wire colors I have described may be different in your setup if the wiring color code convention was not followed. Not too familiar with oil systems or boilers but it would appear from the diagram that your stat is NOT power stealing. One way to tell is to take the batteries out of it. If the display stays lit then it is power stealing, if the display goes dark then it is not power stealing. There is a note on page 11 that says

"The remote sense feature will not work if the system does not provide 24V to the thermostat (example: millivolt heating-only systems or 3-wire zone valves). To use a remote sensor, jumper W922 must be clipped (see figure 10) and the REMT SEN option in the configuration menu must be set on."

Again, your thermostat does not appear to be power stealing based on the diagram you provided. You can make it power steal by doing the following:

1. At the boiler identify the point that the thermostat wires connect to.
2. Find a terminal labeled "c".
3. Take any spare thermostat wire in the bundle and connect it to that terminal.
4. Go to the thermostat and connect the other end of the same wire to the common terminal of the thermostat.
5. In the diagram you provided it appears that the thermostat may not have a common connection.

[Mikepier]

When I do that, the display slowly get dim almost to a point i can't see it anymore, probably from the internal battery to retain programming memory. So what does that mean?

I don't have either

I have done that

If I don't have a C connection, where would the wire connect to?

[Nate Certified Heating and Air]

The light is dimming slowly because there is a capcitor in the thermostat that acts like a battery. Because your thermostat is dimming when you remove the batteries it is most definetly not a power stealing thermostat. You need to get a thermostat that is a power stealing one (one that has a common connection, or "c" terminal). Why are you using a remote sensor anyway? Check this out: