Motor-Driven Steam Zone Valve Mystery, Boiler Not Shutting Down
We've run into a head scratcher for which we are appealing for help.
We have a Burnham V907 that runs continuously and will not shut down. A Taco 501 fires the boiler.
The system has zone valves. Originally 6, but now only two appear to be wired (finished basement so wire tracing very difficult). At least, only two are wired to the 501, which is the only TT lead to the boiler.
If either conductor is removed from the R or W terminal on the 501, the boiler will shut down.
In Photo 1 if BOTH red or Both white conductors from the zone valves are removed from the splice, the boiler will shut down. But not with either singularly.
In Photo 2, if all conductors are removed from zone valve 1, the boiler still runs. Same for zone valve 2, same if all wires removed from both valves: Boiler still runs.
There are no splices between 501 and Photo 1, also no splices between Photo 1 and zone valves. All TT wires tested for possible short. None found. There is no continuity between white & red on any of the TT wires.
We are aware that none of this makes any sense. As for history: All we have is that the 501 was added approximately two years ago. Sometime during the past winter the problem with the boiler not shutting down began. It's an Elk's Lodge, so they now control the boiler with the switch.
But let us set this problem aside for a moment and instead access whether the wiring for the zone valves is even correct?
As a rule, we avoid zone valves and have never installed them, having watched this video from Dan years ago:
Seems to us the cure is worse than the disease.
Does anyone have a schematic for wiring these zone valves properly? It doesn't make sense to use that in Photo 1 there is a connection to a 24v transformer, when both zone valves are connected to transformers via their T5 & T6 terminals. It further doesn't make sense that the zone valve green conductors are not connected to anything in the photo 1. And then there is the yellow conductor at the TT Y terminal, which never appears again (that we can find).
Perhaps if we simply wired the zone valves correctly (assuming it's wrong), the first problem would resolve itself?
Any help greatly appreciated!
Service, Installation, & Restoration of Steam Heating Systems
newenglandsteamworks.com
Comments
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Hello you have power feeding back through relay. Trace it by disconnect all then test after each stage.
Brentharlowbuilder@gmail.com
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Make life easy, ditch the 120v/24v step downdown transformer buy an SR relay box that matches the # of zones you will be using and wire accordingly. The end switch from that new SR control will be the only set of wires now pulling in the boiler.
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Do not worry about zone valves, Dan's example refers to steam not water. I would do what was suggested in getting a Taco Zone control like a ZVC 403 or whatever model matches your zone valve amount. A 403 is 3 zones, a 404 is 4 zones and so on…
Out of curiosity I would perform your experiment of removing the red wire at the thermostats each and see what that does. The zones are obviously wired together somewhere, and the zone valves may be in the manual open except for the operating ones.
LANGAN'S PLUMBING & HEATING LLC
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yeah, double check the wiring. Did it work correctly before now? What is the history here?
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Hard to narrow down the problem. You may have a zone valve with a bad end switch. The guys are right, a zone valve panel would separate the wiring and make it easier to diagnose. If its an end switch… the thermostat signals will be ignored and the boiler would think there is a call for heat and run. I have seen this with Taco zone valves and Honeywell. If you have Taco its the bottom 2 posts that are the end switch ( one wire is actually the common leg of the 24V transformer ). What confuses me is you said if you take the thermostat wire off, the boiler shuts down. When you do that, you deny the zone valve of power on post 1 but the common should stay active. This is a head scratcher. I do believe you will be money ahead by going with a panel. They do have lights that show if the end switch is open or closed. You will be able to check and test right on the landing points. You should be better able to trouble shoot with a panel.
Many of you guys remember what we had to do before zoning panels. It looked like spaghetti with all the wires to zone valves. Quite often all the wires ran to the transformer area for termination and splicing.
I apologize for my ramblings but maybe it will help.
Steve
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Sounds like it might be a stuck relay in the taco box. Could try taping on the one connected to the boiler with the tip of a screwdriver.
I've had this happen to my blower. It was stuck on despite no call going to it. I think in that case I made my thermostat do a call to trigger the taco. Somehow that call unstuck the relay and the blower shutdown after.
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Key piece of information needed. What is the make/model of the zone valves? I don't recognize them from the photos. However, some zone valves are not spring-return to close: they are motor-open and motor-close. They require a compatible thermostat that can send an open signal and then a close signal.
Has the thermostat been replaced? If so, the new stat may not be compatible.
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There is something missing in the pictures shown. Two zone valves should mean you have two thermostats. Zone valves have 5 conductors connected but only the two for 24v are shown connected. Where are the other 3 going? Do you have a model number for the zone valves?
order of operation should be - thermostat opens zone valve, zone valve signals 501 to turn on boiler. Unless there is a cooling system connected the Y and G connections at thermostat are useless.0 -
Try reversing terminals 1&2 on the SR501
I know On my zone system, the wall 24V transformer supplies power for the thermostat loop, the control has it’s own 24V supply to power the zone valve motors.
Interpret how I say it, not how you think it.0 -
Good point John. Is it a smart thermostat? They need 3 wires, one being a common. The power company is giving away free smart stats that need a common. We installed 3 at one house just yesterday. We had to pull a common to all 3. Taco sends a resister on their panel to install on the white wire which eliminates the need for a common.
It could be that simple. Power robbing thermostats require so many VA to operate. The problem is if you run out of VA in the system transformer, all kinds of issues arise.
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These are motor driven zone valves. Standard spring zone valves for hot water and Taco relays not applicable to this situation. Thermostats were changed and are compatible. It used to work.
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
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There are two thermostats, they are identical, so 2nd photo omitted. The other 3 conductors go to the TT. They are motor driven zone valves, one conductor to open, another to close. Standard Honeywell motor driven valves.
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
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Not smart TTs, not the issue. Boiler runs if zone valves and TTs completely disconnected. These are motorized zone valves.
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
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Without attempting to trouble-shoot from a far. Living out yonder in Montana where we hit -35° this past winter, I strive for simplicity and dependability on the control side of my systems. Not only because of the potetntially severe weather, but also because of isolation and the 'out-in-the-country' living relished by many. Indeed, even after installing a brand new system, my next patented question is,"And what are we gonna do for back-up heat ?" With many responding with a blank stare. Common sense is at an all time premium. My personal now-a-days preference for zone valves is in fact the Taco Zone Sentry. Basic trouble shooting made easy. Is the indicator light on ? Is the valve in the open or closed postion ? And for testing, the modular connections make the need for a pocket screw driver a mute point. Not demeaning ANYONE'S product. But, I don't use zone valve relays. Why ? Because simply, how many P&H techs are versed enough to trouble shoot an ESS board ? Ahhhh, being in this biz 55+ years, I'm comfy saying,"Not many.". I hardwire my zone valves end switches to the boiler. This in keeping with the my WW2 submariner, life long oil burner/heatingman father's advice to,"Keep it simple stupid.", the 'KISS' method. A 'call back' is just that. Just saying.
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if that is a normal heat/cool thermostat only operating a hydronic heating system the G terminal should not be connected to anything. I somewhat feel sorry for the rep at the distributor where you go shopping for a “standard” motorized valve.
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The actuators are power open - power close so the Taco ZVC (or other brands) won't work. I have used Honeywell TH5110D-1006 thermostats in the past because they can be programmed for Series 20 system operation. I can't see where the problem is, but I have attached a wiring schematic. Maybe something to do with the "extra" 24V transformer wires?
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We didn't go shopping for it, it is pre-existing, installed by others. Not hydronic, steam heating. Valves are Honeywell ML784, ML984, or ML6984, all valves (standard) = same wiring protocols.
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
newenglandsteamworks.com0 -
Thank you for the wiring diagram. We tried disconnecting the transformer, -no luck.
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
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What is the model of that stat? I’ve not seen a stat that used G as the power close terminal. I’m pretty sure someone did some wiring mods, the way it’s hooked up it would run all the time. You’re going to need that third wire in the pic with the wire nuts to bring power back from w on the zone valve to w on the 501. Make sure the transformers are in phase.
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That's all I got…
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
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the actual connections to the Taco 501 are not shown. If the R/W connections go to the 24v transformer that is your issue. The zone valves cannot control the boiler as they do not have end switches. The 501 is supposed to control the boiler using a thermostat, outdoor controller or simply a switch connected to R/W
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@New England SteamWorks , I looked up the ML6984 actuator manual- it's here:
So far, we've all been assuming these actuators have end switches. But looking at the terminal strips and wiring diagrams, I don't think they do. If that's the case, there is nothing to shut down the boiler when the ZVs close.
We've run into similar situations. Our solution was to substitute a DPDT fan center relay for each ZV's transformer, such as the Honeywell/Resideo R8285B which mounts on a standard 1900 box:
With this setup, the transformer can power both the ZV, and the thermostat if needed. The thermostat operates the R8285B using the usual 2-wire 24V circuit, with common wire if needed. One set of R8285B contacts goes to B-W-R on the ZV to open and close the valve. The other set uses the normally open contacts to control the SR501, in parallel with the other zone valve hookups.
Might be a bit more work than you expected, but it will get the job done using off-the-shelf parts.
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting1 -
Edit: Deleted the irrelevant. Sorry, I was looking at the wrong valve. Looks like 24v control does work but it needs a 3 way controller. It's designed to float. I don't know if you can: use a spdt relay to continuously power closed while the relay is in the normally closed position. Until, the relay switches over to normally open to continuously power open for the call for heat. The continuously powering open or closed is the question. Still don't see an end switch. If the relay control idea works you could use if a DPDT and use one pole as an end switch.
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😀
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
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After re-reading the problem and seeing some other information the solution can be quite simple. Those thermostats are not correct to operate the zone valves. Use one those stats (where it is or relocated) Rh and W connected to R&W on 501. That will control boiler. You indicated multiple other zone valves not connected. If you wish you could find proper stats for the 2 zone valves or simply temporarily jumper R/W or R/B to drive the valve open.
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@Don_4 @Teemok great minds think alike!
@New England SteamWorks , let us know how you make out.
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting
1 -
Thinking this through further @Steamhead, attached is how the 501 is wired to the burner, and how it SHOULD be wired to the zone valves. Except the current ZV wiring appears wrong. If my diagram is followed, a call for heat will energize the the 501 and fire the boiler. When the call ends, the 501 will de-energize, no fan center needed? What's confusing is they say it USED to work. But I can't see how with the current wiring….
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
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I wouldn't do it that way. That diagram would probably work, but it's too easy to fry the transformers (remember the SR501 has its own) if you get wires crossed. When we wire up a multi-transformer situation, we always completely isolate the different 24V circuits from each other. That way, if a component needs replacing, you won't (or shouldn't) fry the transformers.
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting0 -
Got it. I think this is how it is wired now:
Don't see how that could ever work…
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
newenglandsteamworks.com0 -
It can't.
I've often found it's best to just start over on jobs like this. If existing cables can be used, fine, but start connecting things from scratch.
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting
3 -
Agreed, and thank you for all the help @Steamhead !
New England SteamWorks
Service, Installation, & Restoration of Steam Heating Systems
newenglandsteamworks.com0 -
I can't see how it could be currently correctly wired.
The quoted below from the instructions answered my question about if you can continuously power either W or B. You can. You should not power both at the same time. I would use a DPDT relay for each zone valve and existing thermostat combo. One pole of each relay would be wired parallel to the SR501 RW terminals so that when the relay activates POLE #1 send the external trans. 24v power R to B and On Pole #2 it calls to the sr501 by connecting sr501's R and w. When the relay is not activated by the thermostat the trans.24v R would power W to close the valve.
"Operation:
The recommended valve actuator power source is a
class 2, 24V transformer or 28Vdc across terminals
T5 &T6. Internal circuitry provides dc power for the
electronic sensing and drive motor circuits.
The motor is controlled by a microprocessor.
Connecting B to R tells the microprocessor to cause
the actuator to drive open. Connecting W & R will
cause the actuator to drive closed. For "floating"
control, if R remains open, the actuator will remain in
the last position.
At the end of the valve stroke, the actuator will
develop the necessary force for positive valve close
off. As forces are developed, the current to the motor
increases. The microprocessor stops the actuator
automatically when the motor current, and forces
reach the predetermined level."1 -
You need an Auxiliary switch as an end switch for the ML6984
Also the thermostats need to be set up for series60, to power open/close the zone valve
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Another thought on the use of the Taco SR-501 because of the 2 transformer issue - I would suggest an isolation relay like a RIB U1C that can be powered off the transformer for the zone valve and have the N/O dry contacts go to your boiler.
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That would work if you used one RIB for each ZV and wired the dry contacts in parallel. If doing this on a 120V burner circuit the RIB(s) would need to be mounted on a suitable box. The SR501 is already there, so that's why I included it.
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting0 -
@New England SteamWorks, any updates?
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting0
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