A Taco zvc404 puzzler!

brookland718

Hello all,

Looking for some help on my weird multizone heating problem. I have a gass boiler and a 4 zone hydronic system with a zvc404 controller. I have 3 zones in the house and zone 4 is the hot water heater. Each zone has a non smart thermo stat. The whole system is about 20 years old, but has more or less always worked. 

A few years ago I noticed zone 3 seemingly wouldn't work unless zone 2 was on and heating. Today I noticed zone 1 also wont work without zone 2 on. 

The taco shows the tstat light and valve light on for each zone, but what I've noticed is that only zone 2 and zone 4 will trigger the boiler to fire up. Zone 1 and 3 circulate water fine and the tstat lights go on and off fine, but if zone 2 isn't on, the water cools down and the boiler sits idle. I'm fairly certain the hot water heater triggers the boiler fine as the system works fine in the summer when it's just making hot water. 

What in the world could this be? Doesn't seem like a wiring issue. Do I need a new taco? 

Thanks!
Confused in bk

fenkel

purchase a new one.

brookland718

@fenkel so it's pretty much toast? Is this typical of a dead board?

HVACNUT

What make and model zone valves? It could be bad end switches on zones 1 and 3.

brookland718

Yes i did. Sorry didn't expect there to be the same audience! Sounds like it could be bad end switches on the zone 1 and 3 valves. Is there a way to isolate this as the problem?

brookland718

@HVACNUT I'll go check, i know they are the 4 wire Honeywell variety. 

Brent H.

Do the “Valve Open” LEDs turn of for zone 1 & 3? I believe those are controlled by the end switches so if they are working properly I tend to think it is probably the ZVC that’s bad and not the end switches. Give Taco a call and they can assist you. Their support is great and one of them my chime in on this forum.

@SteveSan

brookland718

@Brent H. Yes they do! That is a good point  I was basically convinced it was the end switches but now you have me questioning that! 

SteveSan

@brookland718 Please give Taco Technical Services a call during normal business hours Mon-Fri 8am-5pm EST 401-942-8000. If you can be in front of the control when you call, walk you though some troubleshooting. We will be back live at 1pm EST.

Zman

Put a jumper wire across the terminals that the red wires are connected to and see if the problem goes away. If it does, you have bad end switches. The repair is pretty simple, just swap the powerhead. https://www.supplyhouse.com/Honeywell-Home-40003916-026-Replacement-Head-for-V8043E-Zone-Valves

brookland718

Looks like it's bad end switches. Before I saw @Zman 's suggestion, I tried what @Peakedtoosoon suggested to me earlier which was swapping zone 1 and 2s connection to the valves and I was able to rule out the taco since zone 2 when connected to zone 1 was able to fire the boiler. Zone 1 has a bad end switch. The tip to jump the wires is good! But I think Ive got it now.

Would you replace all of them at once? Or just as they break? I have 4 and 2 will need to be replaced 

Brent H.

Maybe @SteveSan can explain how the LED comes on but the end switch is bad?

brookland718

@Zman any reason I can't keep the 3 and 4 wires jumped on the non firing zones until I can replace the faulty valve head units? Will the taco ignore the jumped wires if the zone isn't active? And if it is active isn't it ok for the end switches to be permanently active? I'm almost failing to see the need for the end switches 

SteveSan

@brookland718 you can leave 3-4 jumped and the boiler will only fire when there is a call and when the call is satisfied will turn off. On a call for heat between 1-2 terminals on the ZVC zone valve connections should see around 24volts or so. When the end switch makes should see the same voltage between 1-3.

Zman

I would want to see more of the system before commenting on bypassing the end switches long-term. Most of the time end switches are not necessary. Do you want to post pictures of the boiler and piping?

brookland718

@SteveSan thanks for the reply. So just to confirm there is no problem jumping the 3-4 terminals (essentially bypassing the end switch signal) semi-permanently? 
I see this is how zone valves without end switches are wired up. What is the point of the end switch then? Especially since they seem to fair somewhat often?

Thanks all!
@Zman I'll shoot a picture of the whole system in the morning.

brookland718

Just a quick report, i jumped the 3 and 4 terminals one zone 1 and 3... This seems to work fine and restored the zones ability to fire the boiler! I read on another older post that the end switches can serve to prevent a boiler call if the valve won't open and I can see a situation where that might happen... But otherwise, it seems fine to live without them for a bit. I've heard bad things about the new Honeywell valves build quality, so I'm debating the long term fix and whether swapping all 4 to a different brand is the right long term solution. Open to suggestions

EdTheHeaterMan

Taco's 571-2 zone valves are not the best choice for the DHW zone. even with priority. They can take over 120 seconds to open in some cases. The Taco Zone Sentry valve opens fast like the Honeywell but has a battery that power closes the valve (Not the spring close like the Honeywell or the Taco 572-2). That battery is a rechargeable and lasts several years. After that, the valve fails open (mostly) and you will need new actuator motors.

If I had your problem, I would replace the Honeywell actuators as they fail.

brookland718

Thanks @EdTheHeaterMan. Does it seem like a horrible idea to keep using the Honeywells with that bad end switch? The valves work fine. 
Now that i know I can bypass the end switch, I'm tempted to keep everything in place until the valves actually fail. 
I read some positive posts here about caleffi valves, but it does seem easier to just replace the Honeywells with Honeywells. 

mattmia2

EdTheHeaterMan said:

Taco's 571-2 zone valves are not the best choice for the DHW zone. even with priority. They can take over 120 seconds to open in some cases. The Taco Zone Sentry valve opens fast like the Honeywell but has a battery that power closes the valve (Not the spring close like the Honeywell or the Taco 572-2). That battery is a rechargeable and lasts several years. After that, the valve fails open (mostly) and you will need new actuator motors.

If I had your problem, I would replace the Honeywell actuators as they fail.

I'm pretty sure it is a capacitor in the zone sentry valves. If they are buying quality caps it should last for decades. If they buy poor quality caps it could fail in a couple years. Easy enough to buy new caps and replace them.

But if they are the honewell valves with removable power heads I would replace the power head. Even if they were the old style i would probably use the retrofit kit to make the power heads replaceable,

brookland718

@Zman see attached pics. This is before I jumped terminal 3-4 on zone 1 and 3.
I understand if one of those valves gets stuck open, there might be a deadhead issues for the pump?
Also really dumb question: does the water in this system circulate up from the valves? Or are they on the return? 

Thanks

mattmia2

In your case the zone valves are on the return.

The issue is that if the zone valve fails to open you can deadhead the circulator, the end switch proves that the valve is open and delays the circulator from coming on until at least one of the valves is open.

HVACNUT

With the circulator motor facing up, you need to keep minimum 20 psi on the system. 

brookland718

@HVACNUT ok thanks for the tip! I had read 13-15psi a while back. System seemed to be working fine under 20, but i charged it up a bit.  the psi changes a bit depending on water temp

 Is the red hand pointing to 40 on the tridicator a boiled shutoff threshold?

brookland718

@mattmia2 ok copy on valves on the return. That's what i thought, but I don't see any others setup this way. 
So if a zone calls for heat and the valve doesn't open, I can have a deadhead for the circulator. But if that happens I won't have heat in that zone, so that would be the indicator? 

I can see this possibly happening, but fairly unlikely as rarely in the winter is only one zone active alone for very long. But it's definitely worth noting And probably means the answer is replacing the Honeywells. 

HVACNUT

brookland718 said:

 Is the red hand pointing to 40 on the tridicator a boiled shutoff threshold?

Move the red indicator to 30 psi which should be the rating on the pressure relief valve.

mattmia2

It will deadhead the circulator during that couple seconds the valve takes to open too. More significant with larger circulators and slower valves.

Valves on the return are less common but not unusual. You close the loop anywhere and flow stops in it. Sometimes you can get enough gravity circulation within the supply pipe to cause unwanted heating.

Zman

I would be comfortable with the end switches jumped in the short term. It is a good idea to have them in a system like yours and they are not difficult or expensive to replace.

Joe Mattiello

Hi everyone, I'm really impressed to see all the support on The Wall...
this is a great forum to share information on and get feedback from some of the best in the industry. Taco also has a tech support department at 401-942-8000 and ask for tech support.
ZVC controls are equipped with diagnostic lights to provide a visual of what is going on in the system. to troubleshoot, validate a demand with a jumper across TT terminals, and see if the boiler fires after approximately 1.5Min. If not, place a jumper across, 3, and 4 terminals on control panel to simulate an end switch closure. these are simple exercises that will not cost anything more than a little bit of your time. If you have gone through these simple exercises, you will know what to replace. It is ok, to run the system with 3, and 4 jumped, but you do lose ability to turn off boiler if the valve is stuck closed.
Hopefully, this was as helpful as all the other comments. thanks for using taco products.

brookland718

@Joe Mattiello absolutely the help here is amazing. Your comment is obviously spot on. I'm running with 2 zones jumped now and debating if i replace the valves now or just wait. I understand the potential deadhead issue if a valve sticks. I'm not sure how big a deal it is for normal operations (short time it takes the valve to open). 

EdTheHeaterMan

@brookland718 On my own home, I would leave it until the winter is over. Then probably forget about it... LOL. but doing any repair that might require shutting down the system completely until the repair is finished, that is not absolutely necessary, in the middle of the winter, if just asking for trouble.