Circuit for 3 Zone Valves, Honeywell aquastat

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Old 12-12-10, 07:49 PM
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Circuit for 3 Zone Valves, Honeywell aquastat

Hi, all,

Last week the aquastat on my boiler stopped high-temp limiting, so I replaced it (later found what looks like a broken cold solder joint), but the new model (Honeywell L8148E1265 replacing L8148E1257) seemed to be not entirely electrically compatible (everything internal looks the same) as the thermostat in the aquastat would chatter in an ugly way when all the zones came on (running one zone only seemed OK).

I installed the boiler (12 years back) but the electrical pre-dated me. Trying to troubleshoot an unlabeled hairball of too-many-wires-per-wirenut, I thought it would be best to re-do the electrical. Turns out it's trickier than I expected. It might have been ugly, but it worked.

Of course none of my reference books come close, and the Honeywell schematics don't cover my exact scenario (their closest ones want to run two zone valves off of the aquastat's transformer and additional ones off of a secondary transformer; my setup has all (3) zone valves (Taco 571-2) on a transformer. I'm planning to add a fourth zone valve/thermostat in the next month to get the kids some heat in their basement playroom (probably with another circulator on a relay, but that's another story).

Based on this Taco diagram (lowest left, page 2):

http://www.taco-hvac.com/track_file....wnload_id=7823

and this description:

The Taco Zone Valve is a 3 TERMINAL zone valve. Follow these steps to wire it:
One terminal of a 24 volt, 40VA transformer is wired to one side of the thermostat. The other side of the thermostat is wired to terminal #1 of the zone valve operator.
The #2 terminal of the zone valve operator goes back to the other terminal of the transformer.
To activate the boiler control, run a wire from the #2 terminal to one of the T terminals of the boiler control.
Run another wire from the #3 terminal of the zone valve to the other T or TV terminal of the boiler control.
I came up with this wiring scheme (future work in grey, not yet installed):

boiler :: boiler_wiring.png picture by bill_mcgonigle - Photobucket

but it doesn't do anything. I can see 24v show up at TV when I turn on a thermostat, but the aquastat doesn't kick on (jumpering TV to T will make it operate correctly). Rather than thrash with yet more trial and error, I thought it would be best to de-lurk from the forum and see if some of my fundamental misunderstandings could be corrected.

Things I know I don't understand:

1) Are T and TV different, or just two interchangeable positions?
2) Is there a convention for which to interrupt with the thermostats, load or common, (as marked on the 24V transformer)?
3) I'm thinking binding the neutrals from the independent transformer side and the boiler side might be causing a problem, but I don't really get how the 'terminal 2' on the zone valve is supposed to be a shared neutral between both circuits without interfering with each other. Or maybe I'm inappropriately binding all the neutrals when I shouldn't be. I'm definitely falling short on this concept.

All suggestions appreciated.

Thanks,
-Bill
 

Last edited by bill_mcgonigle; 12-12-10 at 08:36 PM.
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Old 12-12-10, 10:05 PM
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Hi Bill, apparently the old 1257 (can't find any specs on it) unit had a beefier transformer. I'm sure that the three zone valves was too much load and pulled the tranformer voltage way down.

Personally, I wouldn't use the internal transformer in an aquastat for even one zone valve. It's much easier and cheaper to replace a burned out transformer all by itself than it is to replace the entire aquastat. My choice would always be a separate transformer(s) for ANY/ALL the zone valves, or a zone control panel like the Taco ZVC series...

Your schematic looks correct to me... it should work. Double/triple check your wiring. Have someone else look at it... sometimes we are blinded by our own mistakes.

I can see 24v show up at TV when I turn on a thermostat,
You should see appx 24VAC between T and TV whenever there is NOT a call for heat. It shouldn't just 'show up' when there's a call for heat. When the zone valve opens (and remember Taco valves take a few minutes to open, don't expect it to happen instantly), the voltage between T and TV should go to ZERO (because the endswitch in the zone valve is making contact and shorting them together, much as your test jumper was doing).

If you want to test the valve opening and the endswitch operation, disconnect the wire on terminal 3 of the zone valve. Set your meter for OHMS. Connect the meter from 2 to 3 on the zone valve. Turn up the associated thermostat. When the valve opens, you should see 2 and 3 go from OPEN (infinite ohms) to CLOSED, CONTINUITY (zero ohms). If you don't see this, either the heat motor side of the circuit is wired wrong, or there is a problem with the valve head.

1) Are T and TV different, or just two interchangeable positions?
In your application, they are interchangeable... because you are no longer powering any zone valves with the aquastat. It's only labeled differently so as to know which is which when wiring ZVs from the internal transformer.

2) Is there a convention for which to interrupt with the thermostats, load or common, (as marked on the 24V transformer)?
Not really... since it's low voltage wiring, and unlike house wiring, neither side is referenced to ground (as neutral is in 120VAC circuits), it doesn't really matter. If the transformers happen to be labeled as to which is which, it is of course good practice to use the same convention with all the devices in the system, but some transformers aren't labeled!

3) I'm thinking binding the neutrals from the independent transformer side and the boiler side might be causing a problem, but I don't really get how the 'terminal 2' on the zone valve is supposed to be a shared neutral between both circuits without interfering with each other. Or maybe I'm inappropriately binding all the neutrals when I shouldn't be. I'm definitely falling short on this concept.
You aren't 'completing' any circuits. There will be no current flow between the transformers with only one side connected to each other.

SHARED NEUTRAL: If you are familiar with your 120/240VAC house wiring, realize that there is a 'shared' neutral there also... in this case, the neutral happens to be a CENTER TAP on a single transformer, but for all intents, this COULD be thought of as two separate transformers with one leg of each tied together.
 

Last edited by NJT; 12-13-10 at 04:21 PM.
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Old 12-13-10, 06:48 PM
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Thumbs up

Thanks, NJ Trooper!

Your vote of confidence for my circuit was very helpful.

Learning how to test the zone valve was also key, and I patiently ran the meter to just about every point. It was wired right, but I found out:

a) one of my zone valves takes about 9 minutes to heat up. I read on Taco's site it should take 2. It's on the indirect domestic water heater, so that's not real critical, but I will replace it before long. Now I know how hot they should feel by hand when they're ready.
b) one of my thermostats wasn't functioning (the display was fine, replaced the batteries, but it would never complete the circuit). This is the one in the part of the house with the woodstove, so it's not critical there either, but

wouldn't you know it, I was assuming both of those devices were behaving when I was trying to isolate the problem. Makes it tough. "Don't assume, always measure!"

With that thermostat replaced it appears everything is functioning properly. We can go visit family over Christmas now without worrying about the pipes freezing up.

I've read many of your posts here, and many have been helpful over time. Let me take this opportunity to thank you for them and this one, and note that your talent is apparent. If you have a tip jar somewhere, please PM it to me.

Thanks,
-Bill
 
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Old 12-14-10, 09:04 AM
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Thanks Bill for the kudos... glad you got it going!

How weird that you had those multiple problems!

Enjoy your Holidays, and as for the 'tip jar'... just say a prayer for World Peace, and Pay It Forward... that's enough for me.
 
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