Wiring Configuration - adding Common with Zone Valves


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Old 12-30-14, 05:11 PM
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Wiring Configuration - adding Common with Zone Valves

I went over to the pastor’s house today to install his HW RTH9580WF and RTH6580WF. He has a Weil Mclain Ultra 155 hi-eff gas-fired condensing hot water boiler. Two heating zones. External transformer for two Taco 571 valves. See the attached schematic.

Ttstat wiring had an unused green available. In the schematic, I show the green tie-ins from the tstat to the transformer common. Seemed simple enough.

Then the wheels fell off.

The 6580 allows date/time, even program setup, but it will not look for wifi and it will not show inside temperature at the tstat. Three or four unplug-plugins gave same results. (The unit is OK. I checked it at my home and it plugged in and initialized just fine).

The 9580 initializes and goes through some of the first steps and gives a small message at the lower left that it is “waiting for equipment”. And then it reboots after a minute or so.

Here’s my guess. The Taco zone valves should not be wired as they are. The transformer Load should not run to the middle pins on the valves – it should run to the R at the tstat base. Taco schematics I have seen show it that way. I think the valve controls should be re-wired to have LOAD to Rh/Rc, Common to Pin 2 on valves and Tstats to pin 1 on their respective Valves. Common then would tie in to C from the xfrmr.

The way it is wired now allows Tstat start-up but I think something goes awry when the Taco valve actuates and closes its end switch. I also don’t know if it is related to the Weil Mclain TT connections (they don't use TT on their schematics).

I did check voltages at initial wire up: R to W = 24V, R to C = 24V, and C to W = 0.

Thoughts?
 
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Last edited by DaveSPE; 12-30-14 at 06:10 PM.
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Old 12-30-14, 06:54 PM
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I think I found part of the answer to my problem. The Taco zone valves can't be wired with Tstat Base R tied to terminal 1 on the valve - IF you want to have continuous power to the Tstat via R thru C. Looking at the Taco catalog 100-3, the valve piston shuffles back and forth ever so slightly when the valve is energized to actuate. It cycles, opening and closing the circuit at a snap switch internal to the valve power head between terminals 1 and 2. When the circuit opens, power to R drops out and the Wifi stat needing power from R resets during this momentary loss of power. The valving should be wired per the Taco schematic in 100-3.

As for the other part of my question, I don't want to assume the T T terminals on the Weil Mclain Ultra 155 act like T T terminals on other boilers, so input on this is much appreciated. Thanks.
 
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Old 12-30-14, 07:03 PM
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Your diagram is drawn in-correctly but you seem to have figured out why.
Do you need a new diagram ?

The TT terminals require 24vac to activate the boiler.
 
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Old 12-31-14, 12:06 AM
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http://www.weil-mclain.com/en/multim...ler-manual.pdf

Is this the boiler?
The diagram looks different than the one that you posted.

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Old 12-31-14, 04:02 AM
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Houston - that is the Ultra 155 diagram. I did not pop the 155 cover open to look at the T T connections. Since the system works with the current two-wire stats I wasn't sure if the T T behaved like on other simple gas/oil boilers with an aquastat. But my diagram is of the external zone valving. I was concerned about the proper tie-in to T T. As long as the T T comes from terminals 2 and 3 of the zone valves, does it matter which way the wires are connected? Is there a difference between the T T terminals that would affect operation?

My revised wiring will connect W's at the stat base to term 1 on the valves and xfrmr Load will go to R on the stat bases. Xfrmr C will daisy chain between the valve's terminal 2 and on to T. Term 3 on the valves will remain same to T. Then my new C at the stat base will jump to term 2. I have a revised diagram but not at this PC. Worst case I'm thinking I may have to flip-flop the T T connections to terms 2 and 3 if the voltages look wrong. Does this plan seem OK?
 
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Old 12-31-14, 04:05 AM
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The diagram is actually the in-field connections. It wasn't working with the new stats and after studying the Taco operation I realized why I was seeing stat misbehavior. See my reply to Houston on my proposed revision. Thanks for the help - again!
 
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Old 12-31-14, 06:12 AM
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The boiler diagram looks like it has a different transformer for the 2 stat terminals. Do you think that you may have 2 transformers wired to the two boiler T terminals? (R and W)

I originally drew it as you want to connect it until I saw the way 2 and 3 connect to boiler T and T on the taco manual.

I figured that is why the diagram shows everything backwards, with common wired to stat W and transformer power to power head (actuator) C, and actuator W connected to stat R.

It looks odd to see an external transformer connected to the T terminals without an isolating relay. The boiler is already sending power to a T terminal labeled R. Touching R to W will fire up heat to that zone.

I would definitely measure between actuator center and bottom terminals for more than 28 volts before walking away from the job.

Keep us posted with your results. I am sure that it can help many viewers in the future.
 
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Old 12-31-14, 08:20 AM
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Houston - I sketched up a schematic with how I plan to re-wire the system. The pins 2 and 3 to T T don't really change but I plan to check voltages to ensure a preferred connection. The Taco catalog explains why the two xfrmrs don't interact and it makes sense. The key is for the xfrmr Load/R to go to stat base R and the Valve pin 1 to go to stat base W. Then my Common will always give continuous power to the stat regardless of what the zone valve is doing internally. Thanks, DaveName:  109WashZoneValveSchemFinal.jpg
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Old 01-04-15, 03:57 PM
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This didn't go well. Although the stats saw the continuous power as required, the boiler did not like the T T configuration. I initially connected the T T's as they were originally connected (see schematic in my original post). After nothing happened for a couple minutes of call for heat by the stats, i.e., no circ pumps energized, no boiler flame, just the internal boiler fan, I switched the T T connection. Thank God the electrical designer included fusing in that external T T line or I might have zapped the 155 control board! After a fuse replacement, I rewired zone valving as originally config'd, bailed out and advised to have the service company give it a shot! I'll post what they did to configure it.
 
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Old 01-04-15, 04:24 PM
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I think I'd use a relay...... the NO and C contacts to TT and the coil to terminals two and three on the zone valves.

The relay would be in that cloud in your diagram in post 8.
 
 

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