Two Nest t'stats, Weil McLain boiler & Taco zone valves

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  #1  
Old 09-21-19, 11:18 AM
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Two Nest t'stats, Weil McLain boiler & Taco zone valves

Hello,

Two smart thermostats installation in an existing hot water heating & two zone valves system.
(heating only & no aquastat).

RESULTS:
(NO POWER IN RH WIRE)
TSTAT SEEMS TO BE READING THE REST OF THE WIRES AND INTERNAL BATTERY SEEMS TO BE KEEPING THE CHARGE.

EQUIPMENT:
#1 Weil Mclain Gold CGA (BLR)
(Natural Gas)
#2 Nest Thermostat (3rdGen.) (TSTAT)
#2 Taco 751-2 Zone Valve (ZV)
#2 Transformers 24vac (XFMR)


WIRING LAYOUT:

TSTAT First Floor:
W1 to position #1 in ZV-1stLVL.
RH to C in XFMR for Zone Valves.
C to C in XFMR for Thermostats.
RC to R in XFMR for Thermostats.

TSTAT Second Floor:
W1 to position #1 in ZV-2ndLVL.
RH to C in XFMR for Zone Valves.
C to C in XFMR for Thermostats.
RC to R in XFMR for Thermostats.

BOILER'S MODULE CONTROL.
Wire Harness, #5 wires:
#1-(C)BLACK wire
#1-GREEN wire
#1-BLUE wire-labeled to aquastat
#2-(TT)BLACK wires (#1-RED/#1BLUE-labeled to aquastat)

From BLR TT-wire to position #3 in ZV-1stLVL
and a jumper wire to position #3 in ZV-2ndLVL.

From BLR TT-wire to position #2 in ZV-1stLVL
to a jumper wire to position #2 in ZV-2ndLVL
to a jumper wire to R in XFMR for Zone Valves.

The lever in both zone valves are in the auto position.

Any suggestions or questions please contact me.

Thank you in advance.
 
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  #2  
Old 09-21-19, 11:34 AM
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Welcome to the forums.

I LOVE pictures. It's usually easier to see the wiring then read a description. How-to-insert-pictures
Do you have at least three wires from each stat to the zone valve ?

I didn't see the diagram. Is that exactly what you have ?
You're using an aux transformer to power Rc and C to run the stat...... OK.
The other transformer runs the zone valves. That looks ok.

Those stats should work without the AUX transformer as a test.
 
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Old 09-21-19, 06:56 PM
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Hello,

Iím new and still figuring out how this works, I am using a mobile and probably why the image didnít show properly, that said thank you for the advice.

There are 3 wire connected to the each zone valve and 2 of these wires are connect to the each tstat.
For both levels the same configuration:
ZV position 1 wire connects to W1 In the Nest tstat.
ZV position 2 wire connects to RH In Nest tstat.
ZV position 3 wire connects to one of two TT wire coming from the Boiler.

Ther are two transformers being used, one for the thermostats and the other for the zone valves, are you saying this should work?
If yes, why would it be giving the, no power detected in the RH wire error?
 
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Old 09-21-19, 07:21 PM
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ZV position 2 wire connects to RH In Nest tstat.
No. It connects to the transformer.

Try this........ remove the two wires from the TT terminals at the aquastat. This should leave the circuits operating normally except for activating the boiler. See if the nest recognizes the W1 wire now.
 
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Old 09-22-19, 08:13 AM
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You are absolutely right, the RH wire is connected to the ZV transformer and from the ZV- XFMR itís connected to the position #2 in the Taco ZV. My apologies for not being clear.

There is no aquastat in this system. Should there be one and if so, how come it has been working so far, will it cause problems in the long run, do think I should consider installing one?

Thank you for your replies and help.
 
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Old 09-22-19, 08:44 AM
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No apologies necessary.

Disconnect the two wires that go to the TT terminals. When you see TT terminals it means a thermostat gets connected there. It also means there is an active transformer in that device. We need to make sure that transformer is not interfering with the one running the zone valves.

As another test...... once your nest battery is charged you should be able to disconnect the 24v thermostat transformer and the nest should run on just the W1 and Rh line. It should run on this line for a while before the battery runs down.
 
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Old 09-23-19, 07:23 PM
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1. With the Nest battery fully charged, proceeded to disconnected the Tstat-XFMR, result;
Nest Tstat / Equipment Detected /
NO HVAC CONNECTED
W1 & RH WIRES INSERTED

2. Disconnected TT wires, result:
Nest Tsta / Equipment Detected /
W1, C & RC.

With this last configuration there was no difference between having the TT wires connected or disconnected, makes me think there might be in fact a conflict with the boiler's-XFMR, as you suggested before.
 
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Old 09-23-19, 08:22 PM
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I tried to upload the image again, hope it helps.

Name:  TSTAT WIRING-1.jpg
Views: 11
Size:  193.0 KB
 

Last edited by PJmax; 09-25-19 at 08:30 PM. Reason: modified diagram
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Old 09-23-19, 08:34 PM
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Don't need the diagram.

Ok...... in test 1..... with out the stat transformer connected to Rc and C..... nothing was recognized.
Nothing happened.... no boiler...... correct ?

This is telling us that the boiler's TT terminals are not 24vAC. They are more than likely much lower. Do you have a voltmeter to read the TT voltage ?

With a regular thermostat..... it just shorts the TT terminals so there is no concern about the voltage. The nest has an electronic switch that needs to see 24vAC to create a short for heat.

We may need to add a simple relay between the zone valves and the TT terminals.
 
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Old 09-23-19, 09:31 PM
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From the Weil-McLain installation manual for your boiler.......

When using 3-wire zone valves, install an isolation relay. Connect the zone valve end switch wires to the isolation relay coil. Connect the isolation relay contact across the boiler T-T terminals. Failure to comply can result in damage to boiler components or cause unreliable operation, resulting in severe property damage.
 
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Old 09-24-19, 08:39 AM
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ďNothing happenedÖ no boilerĒ that Is correct.

Toke a reading from the TT wire and the result was 26.7V.

Isolation relay, In your opinion does the 90 380 or 90 340 Fan Relay work for this application or would there be a more specific type and if so which would you recommend. Iíve also been looking at the SR502-4 Taco zone switching relay, would this be a better solution?

Pete, I like to express my appreciation for all the help you have given me so far. Thank you!
 
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Old 09-24-19, 09:42 PM
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Either would work fine. The 90-340 is kind of overkill but it'll work. You just need a 24vAC coil and a single pole relay.
 
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Old 09-25-19, 07:31 PM
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Iím going with the 90 380 relay, Iíve been doing research on a wiring diagram for this specific application but havenít found much on the matter. Could you please point me in the right direction.

Thank in advance!
 
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Old 09-25-19, 08:32 PM
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No problem.

I labeled your diagram in post 7.
The coil (1 & 3) gets power from the zone valves opening.
The N.O. (normally open) contacts (2 & 4) close when the relay gets power.
 
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