Having trouble with Nest thermostats and Taco Relay

amitg

Hello,

I am not a contractor. I just moved into a new construction house. I have 5 zones (5 3rd gen Nest thermostats) with a Taco 6 zone relay (SR506). For some reason, the taco relay for Zone 6 kept flickering constantly when it was on. My contractor swapped out the thermostat for now and replaced with a dumb one saying that the relay is getting confused because both the air handler and the thermostat are trying to trigger it. Now Zone 5 is doing the same thing. I can’t imagine this is an unsolved problem. Is this not an issue with Ecobee4 thermostat? I don’t mind flipping off Nest if it resolves the issue. Please advise. I am pretty bad at this stuff so apologies if something doesn’t make sense.

I have a condensing boiler and on the nest, I have the settings set to Electric heater with forced air.

Jamie Hall

If this is hot water with a boiler, forced air and electric heat aren't correct. There should be a setting for hot water. One hopes. Although with a Nest...

Which is the next question. How are the Nests powered? Unless they have a power source independent of the Taco relay -- at least three wires, one of which is common -- they simply aren't going to work right, if at all. The Ecobees seem to be a little less fractious that way, but any "smart" wi-fi connected thermostat takes a lot of power, and without a power source they just aren't reliable.

SteveSan

If you have 5 Nest, the on-board transformer isn't enough to power the 5 Nest. You would need an external transformer. Please call Taco Tech Support 401-942-8000. We are available Mon-Fri 8am-5pm EST.

amitg

Thank you. As per my contractor We are not using the common wire from taco. It is being supplied from the air handlers.

Jamie Hall

Which brings up a question... is the common from the air handler part of the same power circuit as the Nests? and the Taco?

HomerJSmith

The Nest's have a R, W, C connections. The SR506 has a R,W, C connections for the thermostats. You need a 3 conductor thermostat wire to the Nest from the SR506. The charging circuit for the Nest is R & C connection. If you only have 2 conductors, you need an auxiliary plug in transformer.

HVACNUT

Connections at the thermostats from the air handlers.
Rc, C, Y, G

Connections at the thermostats from the SR506.
RH, W

The Nests should recognize this as you go through the Nest set up procedure.

jstratz

I have seen this happen with a power stealing setup on a Taco relay. Every smart thermostat I have seen does exactly as your contractor said, takes common from the cooling side. So unless Nest is opposite you have an odd problem. Not power stealing from the Taco and not powered off the Taco should only cause the chatter if you are overloading the air handler transformer. Unless only one Tstat is tied to the air handler and the rest are powered from the Taco?

amitg

Here is what my Nest is showing for wiring. I have 5 air handlers - 2 in the attic and 3 in the basement and all 5 are providing power to the Tstats.

amitg

Here is what my Nest is showing for wiring. I have 5 air handlers - 2 in the attic and 3 in the basement and all 5 are providing power to the Tstats.

amitg

I have 5 air handlers - 2 in the attic and 3 in the basement and all 5 are providing power to the Tstats.

I have the following wiring showing on the nest:
Y1 - cool
G - fan
Rc - Power
W1 - Heat
C - 24v common
Rh - power

jstratz

Called Nest to double check and they said with dual transformer systems the C is on the cooling side. Odd one. Bad power from somewhere