Taco ZVC403-4

Bill1856

I just installed a taco zvc403-4 controller and am having an issue. I have my first floor t-stat hooked up to zone 3 for priority. I added the basement to zone 2. When I fired up the system I tried zone 3 first. No problems, t-stat called for heat, valve opened, boiler fired. I shut it down and tried zone 2. The t-stat called for heat, the light when on on the zvc and then went off. I tried again and blew the fuse on the zvc. Checked all the wiring and moved everything to zone 1. Same problem. Any ideas?

Bill1856

Also, I'm using two Taco 3 wire zone valves.

hot_rod

Try taking it off priority if possible. Sometimes the priority function causes a problem.

I know it does with the WR 1361 valves, they lose their common path and will not screw close. But it doesn't cause a fuse to blow?

Paul48

There's gotta be a short. Get the ohm meter out, and start checking.

Bill1856

Hot rod, would it make sense that the priority zone was the one that was working, though?

No other voltage to the thermostat.

Bill1856

Here's a pic.

Bill1856

Both thermostats are Honeywell RHT2300B, wired directly to the ZVC. I only have one fuse left and can't get any more till tomorrow so I'm hesitant to do too much troubleshooting today. It turns out the thermostat fried when the fuse blew, too. Perhaps zones 1 and 2 are running over voltage? Don't have a meter till later today. I kept the upstairs tstat on the priority zone and wire the downstairs zone valve to the same zone and it's working. So that eliminates the valve as an issue.

hot_rod

Sounds like you have something mis-wired? Really one one way to fry a t-stat, unless you applied line voltage?

Bill1856

Alright, took a chance and jumpered the r and w on zone 1. Got the t1 light to light, but the zone valve light did not illuminate. Does it make any sense that zone three, with all the same components, is working and 1 and 2 aren't? Checked all the wires and connections, no frays or shorts.

Hilly

I know you wired those 3-wire zone valves the same color on 1,2,3 terminals but are you 100% sure the wiring is the same on the zone valve end of it? Worth a double check considering the thermostat is giving the go ahead.

Bill1856

Yes. I've checked every connection and color. Made sure they're stripped clean, no frays. Finally got to check voltage. All three zone are identical at the t-stat terminals at the panel and at the t-stats. Totally stumped.

4Johnpipe

Where does the end switch connect to the boiler? is there another transformer possibly in line with that connection? What voltage do you get when you manually open the zone valves?

Joe Mattiello

Good Morning
I just arrived at the office, and decided to check out the wall. I had a funny feeling someone was having wiring issues I see this type of stuff all the time. The best advice I have for you; take all the wires off, of zones 2, and 1: If you have to strip the control completely.
After removing thermostat, and zone-valve wiring from the control you can perform some diagnostic exercises with a couple of short pieces of wire. Place a jumper across the thermoset terminals, and a jumper across # 3, and 5 at the bottom of the control (end-switch terminals) to simulate an end-switch closure. The main, and pump end switch should close. You can validate closure by measuring continuity, or if the boiler fired.
If your diagnostic exercises went well, the control board is working fine, and you know you have a wiring issue. You can methodically place the thermostats back onto the control, and corresponding zone-valves until you have identified the root cause of fuse failure. If you experience any issues with the thermostat acting erratically, or not closing R, & W, you might need to place a resistor across W, and Com terminals to provide a trickle of voltage to thermostat to mitigate any issues.
Hopefully this was helpful. If you’re still having issues, give me a call at Taco, 401-942-8000

Bill1856

I put a jumper between r and w on the zone one t-stat terminal. The fuse blew after about 45 seconds....

TacoJones

It sounds like a failure in the zone valve. The short you're probably looking for is across the 1 & 2 terminals of the Taco zone valve.

Bill1856

The zone valve never opened. It takes about 1:20 for the valve to open on zone 3, which works fine. I've wired both valves individually to the working zone (3) and they both work on that zone.

Bill1856

Ok. So I've got this happening: if only one valve and one thermostat are hooked up, regardless of the zone, the system works. As soon as I hook up a second zone valve, to either other zone, I blow the fuse.

TacoJones

Take the thermostats out of the equation. Place a wire between R & W to trigger each zone on without any zone valves wiring attached and place a wire between 3 & 4 on the zone valve side. That will ensure the board is working properly. The yellow Thermostat light will come on along with the red Valve light. Use your multimeter to check your wiring to the zone valves, determine there isn't a short, along with checking for nicks in the wire that may short it to the chaise of the board. By now there shouldn't be any wires connected to the zone valve, check the resistance across terminals 1 & 2 on the valve head. You will find between 18 & 23 Ohms to achieve proper operation. Make sure none of the levers are in the OPEN, or down, position. They must be in the AUTO, or up, position if you are applying power to the heads.

Bill1856

Found the problem. Turns out one of the wire staples holding the zone valve wires was tight and was causing an intermittent short to one of the zones. That explains why it worked when I switched the wires and worked a few times on the original wire. It was the staple right above the valve so every time I messed with or checked the wires at the valve, it was fixing or causing the short. Thank you all very much for taking the time to help me troubleshoot the problem. Your suggestions were all very helpful.

Zman

Joe Mattiello said:

Good Morning
I just arrived at the office, and decided to check out the wall. I had a funny feeling someone was having wiring issues I see this type of stuff all the time. The best advice I have for you; take all the wires off, of zones 2, and 1: If you have to strip the control completely.
After removing thermostat, and zone-valve wiring from the control you can perform some diagnostic exercises with a couple of short pieces of wire. Place a jumper across the thermoset terminals, and a jumper across # 3, and 5 at the bottom of the control (end-switch terminals) to simulate an end-switch closure. The main, and pump end switch should close. You can validate closure by measuring continuity, or if the boiler fired.
If your diagnostic exercises went well, the control board is working fine, and you know you have a wiring issue. You can methodically place the thermostats back onto the control, and corresponding zone-valves until you have identified the root cause of fuse failure. If you experience any issues with the thermostat acting erratically, or not closing R, & W, you might need to place a resistor across W, and Com terminals to provide a trickle of voltage to thermostat to mitigate any issues.
Hopefully this was helpful. If you’re still having issues, give me a call at Taco, 401-942-8000

@Joe Mattiello thanks for posting. It good to know you guys are paying attention.

Hilly

Great follow up from Taco.
Bill1856 thanks for updating, I like when a thread has closure.

hot_rod

One other point if I may, the resistor between W& Com is often needed to dissipate the voltage coming back from power sealing t- stats.

If you connect a power stealing T stat with two conductor wire the stat sends some current back down the one conductor, using it as a common essentially.

We have measured that current as high as 18 V on some stats in the off position! That can be enough "leaked voltage" to cause a relay to buzz, lights to flicker, or even pull in the relay when there is no heat demand.

The resistor, which are usually included in the box with the T-stat turns that "stray" voltage into heat. So don't touch it, or put your tongue against it

Best to wire power stealing t-stats with 3 wires, power, common, switched leg, to provide a dedicated common.
Nest finally acknowledges that.

Some brands of relay boards now include a 750 ohm, 3 W pull down resistor populated right on the board, no need to wire one into the T-stat connections anymore, or use the various ones in the t-stat package.