Taco zone zvc406 valve system flashing yellow light for nest thermostats zones

pwaghwani

Hello,

I have a weird issue going on with my heating system. I have a 6 zone valve gas heating system with steam boiler and baseboard heats/radiators across the house.

Recently, I have started to replace the Honeywell thermostats with google nest thermostats.

I have installed two google 3rd gen and two E gen thermostats.

For some reason, the taco valve couldn't power on the 3rd gen thermostats but they work fine for E gen thermostat so I powered the 3rd gen with the AC/handler wires.

My problem is that when not in use, I am seeing yellow light flashing on my taco valve system for both E gen thermostats, however, when the heat is turned on at the req temp, the yellow light becomes solid, then the red light comes on and heat seems to be working through radiators.

Is the flashing yellow light normal or is there anything I should do to fix this?

Thanks!

Jamie Hall

The Nest thermostats -- any combination -- must have a common wire (C) in addition to the R and W wires for the heat -- in this case, the R and W are the zone valves. Provided the W and C for the thermostat come off the same transformer, it may work...

pwaghwani

The heat works and the thermostat is powered on as well however my only concern is about the flashing yellow light on the zone valve when its not in use. This didn’t happen with the old honeywell thermostats.

Nest says that thermostats should work without requiring c wire.

Jamie Hall

pwaghwani said:

T...
Nest says that thermostats should work without requiring c wire.

Not in our experience.

pwaghwani

okay.. Well in my case the issue is more about the zone flashing yellow light on the taco valve system when the heat is not in use. But when in use, it becomes solid yellow, then the red light comes up and heats starts which is how it should be.

gaabbee

Is yours on zone 5 and 6 by any chance? I have the same thing on mine but seems to work fine so I've never messed with it. I have honeywell wifi stats not nests

Zman

My guess is that because the nest has no common, it is stealing a little power which is causing the light to flash on the taco.

pwaghwani

gaabbee said:

Is yours on zone 5 and 6 by any chance? I have the same thing on mine but seems to work fine so I've never messed with it. I have honeywell wifi stats not nests

I have a 6 zone. The old honeywell thermostats worked fine but the nest E seems to have some issue. Do you have a c wire connected to your honeywell thermostats?

pwaghwani

Zman said:

My guess is that because the nest has no common, it is stealing a little power which is causing the light to flash on the taco.

I am thinking that could be the reason. Could that create any problem on the taco valve unit? I checked the wiring and there is no C wire so the only option I may have is to hardwire it directly via external transformer.

hot_rod

Certain combinations of t-stats and relays can cause that leakage. With our first generation relay box we had to send out "pull down" resistors to "shed" that strays current that cause flickering. We engineered a solution that is now populated on the circuit board.

A dedicated common seems to solve the problem also.

The 3 wire type zone valves are the trickiest to solve, if that is what you have. The 6 connection "continuous spin" White Rogers can also be a challenge.

gaabbee

pwaghwani said:

gaabbee said:

Is yours on zone 5 and 6 by any chance? I have the same thing on mine but seems to work fine so I've never messed with it. I have honeywell wifi stats not nests

I have a 6 zone. The old honeywell thermostats worked fine but the nest E seems to have some issue. Do you have a c wire connected to your honeywell thermostats?

Yes all have common wires and all are the same thermostats. For some reason it only happens on 2 of the zones. Doesn't seem to change anything and everything operates well.

pwaghwani

gaabbee said:

pwaghwani said:

gaabbee said:

Is yours on zone 5 and 6 by any chance? I have the same thing on mine but seems to work fine so I've never messed with it. I have honeywell wifi stats not nests

I have a 6 zone. The old Honeywell thermostats worked fine but the nest E seems to have some issue. Do you have a c wire connected to your Honeywell thermostats?

Yes all have common wires and all are the same thermostats. For some reason, it only happens on 2 of the zones. Doesn't seem to change anything and everything operates well.

I see okay. Yeah, my system doesn't have any C wires but it seems to power it up. Maybe it's not powering enough, not sure.

One of the E thermostats, still has heat coming on even though the temp set is lower. For eg: if I set it at 70F, and the room temp is 73F, the heat will still be on. On the taco valve unit system and the red light is off for that zone but the switch/valve which opens and close was only half-closed.

The only to fix that is by increasing the temperature to 75F on the E thermostat (room temp is 73F) temp and then the red light comes on, the valve opens up and after few mins, I reduce the heat back to 70F and then the valve closes properly.

Has this happened with you?

Zman

I am surprised one of the @SteveThomas Taco guys have not chimed in. If you are not hearing relay chattering, while this is happening, it probably is not hurting anything. It is possible it will shorten the life of the controller.

pwaghwani

Zman said:

I am surprised one of the @SteveThomas Taco guys have not chimed in. If you are not hearing relay chattering, while this is happening, it probably is not hurting anything. It is possible it will shorten the life of the controller.

thanks @Zman . What would the relay chattering sound like? I don't really hear anything other than the sound of opening and closing of the valves and the sound from the gas heating system.

@SteveThomas - do you have any suggestions for my issue? thanks!

pwaghwani

Zman said:

I am surprised one of the @SteveThomas Taco guys have not chimed in. If you are not hearing relay chattering, while this is happening, it probably is not hurting anything. It is possible it will shorten the life of the controller.

I have started hearing the chattering where the valve is opening and closing by itself. It stopped when i powered off the thermostat. It seems I def need to install a C wire to provide enough power. How should I do this?

Zman

How many conductors are running to the t-stat?

pwaghwani

Zman said:

How many conductors are running to the t-stat?

you mean wires? I can see only two red and white for heating.

I have a 6 zone system:
4 zones have Google E thermostat doing only heating and being powered by the zvc406 taco unit.
2 zones have Google 3rd gen doing both heating and cooling and are being powered by the air handler.

hot_rod

If the stats do not have a dedicated common, they "search" for a common thru the other switched wire. That can cause some odd symptoms.

Not all relay boxes give you easy access to a common without cutting into the transformer wiring.

Also be sure you have enough transformer Va to power all the loads connected. Some of those power stealing stats are energy hungry. The thermostat spec sheet should give you the power draw. Same with the valves connected.

pwaghwani

> @hot_rod said:
> If the stats do not have a dedicated common, they "search" for a common thru the other switched wire. That can cause some odd symptoms.
>
> Not all relay boxes give you easy access to a common without cutting into the transformer wiring.
>
> Also be sure you have enough transformer Va to power all the loads connected. Some of those power stealing stats are energy hungry. The thermostat spec sheet should give you the power draw. Same with the valves connected.

Thanks! Thats a good point. I will check the transformer and see if it can support and provide power to the five thermostats.

I have no C wires. I am thinking of running new wires to all thermostats. Do you think this will fix it?

One company told me that the open and close of valve on taco unit is not compatible with google nest.

hot_rod

Here is how Nest explains the compatibility issues.
I suppose Taco would know or have tested their relay boards with various, common stats? Did you try them?

Possibly Nest has tried hydronic relay boards, although these listed seem to be air side relays.

It really comes down to who you talk with at Nest, and their actual hands on knowledge of the product. There are some sharp support people there once you get a first name, to ask for They grabbed some engineers from Honeywell early on, so there is some experience there.

https://support.google.com/googlenest/answer/9246656?hl=en&ref_topic=9361965


At Caleffi we buy all sorts of thermostats, take them to our lab and test compatibility with our relays. Probably a few file cabinets full of t-stats up in Milwaukee now. That eliminates any guess work when doing tech support.

FaceTime us and we will take your brand and model of stat to the lab and show you how it should wire and assure it works with our product.
Although currently the lab is being remodeled. Dan, Cody, Greg can help with phone support on our relays.

pwaghwani

> @hot_rod said:
> Here is how Nest explains the compatibility issues.
> I suppose Taco would know or have tested their relay boards with various, common stats? Did you try them?
>
> Possibly Nest has tried hydronic relay boards, although these listed seem to be air side relays.
>
> It really comes down to who you talk with at Nest, and their actual hands on knowledge of the product. There are some sharp support people there once you get a first name, to ask for They grabbed some engineers from Honeywell early on, so there is some experience there.
>
> https://support.google.com/googlenest/answer/9246656?hl=en&ref_topic=9361965
>
>
> At Caleffi we buy all sorts of thermostats, take them to our lab and test compatibility with our relays. Probably a few file cabinets full of t-stats up in Milwaukee now. That eliminates any guess work when doing tech support.
>
> FaceTime us and we will take your brand and model of stat to the lab and show you how it should wire and assure it works with our product.
> Although currently the lab is being remodeled. Dan, Cody, Greg can help with phone support on our relays.

I spoke to taco tech support and the rep made it clear that i need to have conductor wires ( C-wire) for google thermostats.

He also said to make sure the transformer can handle the load of all thermostats otherwise i will have to add an external transformer.

I have a hvac tech coming tomorrow so will keep you posted.

Thanks all for your help.

pwaghwani

The taco valve control has two builtin 24v 40Va transformers. Does anyone know if 80va is enough to power for 5 Google E thermostats?

If i need to add external 40va transformers, how many do i need? Thanks!

hot_rod

Rumor is when the stats go into battery recharge mode they pull a bit more current. IF all stats happen to go into that mode at the exact time, I suppose it could add up to more than the transformer can offer?
I don't know what the current draw is or for how long in that recharge mode? Does the spec sheet show that info? If you can find out from Nest, let us all know.

SteveSan

You should be fine using the 5 Nest t-stats. We tested 6 Nest on a ZVC406-4 with no issues. Just make sure the Nest have been pre-charged and have a common wire tied to our board. If you need a resistor, our 1000ohm 1/2watt resistor won't work with the Nest. Nest suggests using a 220ohm 5watt resistor across the W-C terminals on the Taco board.

pwaghwani

SteveSan said:

You should be fine using the 5 Nest t-stats. We tested 6 Nest on a ZVC406-4 with no issues. Just make sure the Nest have been pre-charged and have a common wire tied to our board. If you need a resistor, our 1000ohm 1/2watt resistor won't work with the Nest. Nest suggests using a 220ohm 5watt resistor across the W-C terminals on the Taco board.

thanks, @SteveSan and @hot_rod . I had the HVAC guy over and he said that installing new wires will cost me $ of dollars and he proposed the following solution:

He will install three external 40 va transformers powered up 120 volts and connect two thermostats to each transformer via the red conductor cable.

I currently only have two conductors - red and white so one will get power directly from the transformer and other will be for the heat.

What do you guys think of this solution? thanks!

HomerJSmith

The heating circuit is thru the R & W connections and the charging circuit is thru the R & C connections. Since you have only two conductors to the Nest and the third charging wire is missing, you have to charge thru the W wire. (Just to be sure, you looked in the wall and made sure you only have two conductor wire and that other wires are not hiding behind the drywall. Sometime they are push into the wall cavity.)
The original Taco ESP series 1 zone valve had a charging problem and the recommendations were to put a 220 ohm 1/4 watt resistor to keep the capacitor charged. I would have to look this up.
What the resistor does is steal a little current from the transformer thru the relay coil in the ZVC 406. 5 watt resistor seem to me to be a bit hefty. You probably couldn't fit it in the Nest case. You would probably have to put in the wall.
Nobody publishes their schematics. They just give you a connection diagram.
This is my thinking.

Jamie Hall

Look. To charge the Nest -- or any other wifi thermostat, for that matter -- you need to have a transformer -- somewhere -- and a circuit to the thermostat which is complete. That is, the current will go through one wire -- colour is irrelevant -- to the thermostat, through the thermostat, and back to the transformer through another wire. Those two wires are connected to C and to R, Rh, or Rc depending on the exact thermostat. In a heating circuit, the wire connected usually to W is energized by the thermostat when heat is called for, and is connect variously to a zone valve, relay box, TT on a burner control, or what have you -- and the circuit is completed back to the transformer common terminal with another wire (the common terminal being the one you hooked up to the C terminal on the thermostat).

There are a variety of ingenious ways to do the wiring -- but the bottom line is absurdly simple: the thermostat must have constant 24 vac power between C and one of the three possible R terminals. There must also be a switched wire to carry the signal back to whatever to turn it on to get heat, whence -- in most cases -- it will go back to the common terminal on the 24 vac source.

Two wires, no matter how creative you get, simply will not do the job.

pwaghwani

Jamie Hall said:

Look. To charge the Nest -- or any other wifi thermostat, for that matter -- you need to have a transformer -- somewhere -- and a circuit to the thermostat which is complete. That is, the current will go through one wire -- colour is irrelevant -- to the thermostat, through the thermostat, and back to the transformer through another wire. Those two wires are connected to C and to R, Rh, or Rc depending on the exact thermostat. In a heating circuit, the wire connected usually to W is energized by the thermostat when heat is called for, and is connect variously to a zone valve, relay box, TT on a burner control, or what have you -- and the circuit is completed back to the transformer common terminal with another wire (the common terminal being the one you hooked up to the C terminal on the thermostat).

There are a variety of ingenious ways to do the wiring -- but the bottom line is absurdly simple: the thermostat must have constant 24 vac power between C and one of the three possible R terminals. There must also be a switched wire to carry the signal back to whatever to turn it on to get heat, whence -- in most cases -- it will go back to the common terminal on the 24 vac source.

Two wires, no matter how creative you get, simply will not do the job.

thanks @Jamie Hall and @HomerJSmith for your comment. I really appreciate it. I had a doubt about the suggestion that i got from the hvac guy that it wouldn't be this easy. I have only two conductors running to the thermostats from the taco sentry. I have another hvac company coming tomorrow. I will see if i can run a new wire if possible.

HomerJSmith

Jamie, what you say is partially true. The connection diagram below was provided by me from NEST engineers. It applies to a furnace, but just as well applies to a boiler.
As you can see, 24V goes to the R connection on the Nest. There is a connection circuit (not shown) that is temperature sensitive. When the temp is below set point, the circuit closed and the current goes back thru to the relay coil from the W connection to the common on the transformer and closes the points activating the boiler circuitry providing heat.
I looked up Taco constant charge resistor. It was White, brown,brown = 910 ohms, 1/4 watt. I would try something similar to that rating resistor between C & W connection on the Nest. What Steve San talked about is different.
You might take a volt meter and put the probes on the C & W screws of the Nest. You should get some kind of voltage reading.
You want just enough current to charge the Nest, but not enough to activate the relay. I'm not sure that it will work.

tim w

Nest stats are too smart for their own good, do crazy things sometimes, can drive u nuts!!!!

Jamie Hall

@HomerJSmith -- what you say is true, of course. If you can get just enough current on there to charge the Nest, but not trip the relay, it will work. If. But that will depend critically on the exact value of the pullin current on the relay -- which is not, and is not intended to be, constant. As I say -- and you say -- if you get it just right, for a particular relay, it will work.

It is also about as close a definition of "kludge, kludge to the max." as you are likely to hit in heating work.

HomerJSmith

I would probably start with a 1K ohm 1/4 watt resistor with one lead tied to the W screw and then use my RMS meter set on current and touch one probe to the other lead of the resistor and the other probe to the C screw and read the current.
You could run this idea with the Nest engineers.

pwaghwani

Hi All,

I installed four new five conductor wires for my four nest thermostats on the first and second floor and installed a 40va transformer on the second floor to power two add'l thermostats on the second floor.

The taco board was crashing with just four thermostats so the tech installed three isolation relays and it worked fine after that -- though I still don't quite understand how the relays work.

I am happy with the job he did. thanks everyone for your help!

Mike_I

After reading this thread I'm wondering if ZVC406 still needs a resistor to make this setup work. I have a common from the air handler that I can use but I'm still running into the flickering that started this thread.

Tom_133

I am resurrecting this thread because I am in the same flicker, and sentry zone valves opening with no call. Nest E Tstats, and ZVC 406-4. Four have C-wires and 3 outta the 4 work. Two do not have a C-wire and this thing is tormenting me. Does anyone have a KNOWN solution for a work around?

pecmsg

Why is it always a N E S T?
that might be the problem!

Jamie Hall

Junk the Nests?

pedmec

the thermostats are trying to recharge the internal battery. its called pulsing the thermostat, basically on/off relay fast. because it doesn't have a c common most electronic based controls sense the pulse so its because pulsing is turning on the system to energize the battery

hot_rod

Frustrating about the Nest is trying to get info from tech support. I’m not sure anyone at support really understands how they work. We have received various explanations.

The mist logical one suggested the battery drains and eventually goes into a fast charge mode that pulls high current, not a slow trickle.

Others tell us it has been re engineered and no longer pulls that high current. There are a number of different versions, but no one knows or will tell how they differ as far as internal logic changes 

We have had them work fine for a year or more then suddenly start popping transformer fuses of frying transformers. Perhaps the battery lasts that long before it tries to recharge?

Tom_133

this is a headache only in that I didnt notice all 6 zones were nests before I took on the job. Just after the boiler is on the lawn homeowner asks "will this system work with my thermostats?" I said rather quickly "sure, no problem. What do you have for Stats?" Then my heart sunk... I am willing to buy another control if the caleffi version works. I just want this to work. Any suggestions on Thermostats that work, and are like nest in that he can monitor all zones on his computer?

hot_rod

Tom_133 said:

this is a headache only in that I didnt notice all 6 zones were nests before I took on the job. Just after the boiler is on the lawn homeowner asks "will this system work with my thermostats?" I said rather quickly "sure, no problem. What do you have for Stats?" Then my heart sunk... I am willing to buy another control if the caleffi version works. I just want this to work. Any suggestions on Thermostats that work, and are like nest in that he can monitor all zones on his computer?

It is hit and miss with the Caleffi relays also
 We do have two 40 Va transformers in parallel so you have 80 Va across all terminals
We added the resistors onto the board, so you don’t need to wire those
There are both surge and self resetting fuses on the transformer
But still, ocassionally we get calls with failures.
It could miswired or older versions of the Nest.  it’s hard to tell on a phone call🥴
High current Gold top zone valves need to be accounted for in the load on the transformer

A dedicated “C” wire is a must and solves most issues, the Caleffi boards have C terminals for each stat

When all else fails, separate power and iso relays.