Taco ZVC406 Priority Mode - Shuts off boiler when activating priority?

kipper

Just installed a Taco ZVC406-EXP-4 zone controller. I have PRIORITY ON and PRIORITY PROTECTION ON. Burnham LP boiler, Superstor 60gal indirect DHW storage tank, combination of in-floor and baseboard radiant, 2 heating zones.

Ive noticed while the Zone 1 in-floor is calling for heat, the boiler is running, and Priority DHW starts calling, the boiler shuts off for a brief period (5-10sec) while the Taco waits for the Zone 6 DHW zone valve end switch to complete. The boiler then fires back up to satisfy the DHW call. When DHW is satisfied, the boiler shuts off, switches back to Zone 1 t-stat call, and fires up the boiler again. Seems like the boiler should remain on during this process?

Is this normal? Should I jumper the end switch on Zone 6 and ignore the Zone 6 zone valve end switch? Not sure if this would fix it, and seems like a bad idea and may lead to the DHW constantly calling for heat if the zone valve fails.

Thoughts? Here's a photo for reference. Ignore the mess, I'm still in the testing phase

STEVEusaPA

You shouldn't jumper the end switch.
Do you still get the delays when zone 2 calls? If not, maybe the zone valve head is bad (bad end switch)?
How about if you switch off priority?
Do you actually need priority?

kipper

STEVEusaPA said:

You shouldn't jumper the end switch.
Do you still get the delays when zone 2 calls? If not, maybe the zone valve head is bad (bad end switch)?
How about if you switch off priority?
Do you actually need priority?

The zone valve head is brand new, and when the zone 6 valve opens and the end switch clicks, the valve open LED on the Taco lights up, so I dont think this is it. I havent tried without priority on, but my guess is it'll run both Zone 1 and 6 simultaneously. No, I dont really need priority at this time, 60gal is plenty for two of us, but maybe in the future as my household grows.

I'm still wondering, is the Taco Priority designed to fully stop the boiler during a Non-Priority > Priority > Non-Priority situation?

Tom_133

If im understanding correctly, you are saying that when the boiler comes off priority it shuts off then theres a delay then it kicks back on with zone 1. Even though zone 1 hasn't stopped calling.

If I have that right than it makes perfect sense. Zone 1 is off while it prioritizes and when the call for priority is satisfied, then the zone valve for zone 1 gets powered the motor spins, hits the end switch and then it calls again. That takes 5-10 seconds.

If you dont want the delay you got to shut off the priority.

lchmb

I'm guessing once zone 6 on priority see's a call it shut's off all other zones.. Of course this will drop out t-t to the boiler. I've never honestly watched this happen but it makes sense. It wont call t-t on til it know's its open. Are you using a condensing boiler and if so, are you using multiple temps? If you have a 60 gallon tank with a mixing valve I wouldn't use priority anyway..

Zman

@SteveThomas or one of the other Taco guys could verify that the controller is operating as designed.
If your system is piped in a way that failure of the DHW valve will not damage anything, I don't see a problem jumping the end switch. If it would cause a circ to deadhead or a boiler to not get the required flow, I would not. It just depends on your setup.

ChasMan

Is the priority end switch closing when the aqua stat calls? Or just when the end switch closes? The manual says it closes whenever there is a call for heat on the priority zone. Perhaps you could wire them in parallel. If that does not work, the only other thing I can think of is have the aqua stat switch on the DHW zone valve and then wire the zone valve's end switch to the thermostat terminals and jump the end switch for that priority zone. That way the priority call would not hit the ZVC until the DHW valve is open.

1sttimeposter

Our system does this too. We also have a zone controller.

As soon as DHW priority calls when other zone(s) on, flame from boiler goes out, goes thru its post-purge and shuts off.

Then restarts immediately with the pre-purge, ignition, gas valve and then flame on to satisfy DHW.

When DHW satisfies, at this stage, if zones still require heat, flame from boiler goes out, goes thru its post-purge and shuts off and restarts right back up immediately after with pre-purge, igniting...

Not sure if it's normal. Wish it does not do that.

Dave H_2

This does sound normal. The -EXP controllers have two independant "XX" end switches.
One for a heat call and the second for a Priority call.

These are two different circuits on the board. The idea is on a boiler that has two independent inputs. When the heat call occurs, the boiler (if it has outdoor reset) fires and modulates based upon outdoor temperature.
The the DHW calls, the second end switch is closed and the boiler will not look at the outdoor reset system and then go to full fire.

The reason for the delay is the different circuits and to wait for the zone valve to open to allow flow to occur. If it remained firing and the zone valve was closed, there would be no place for the heat to go.

Dave H.

newagedawn

looks like your priority zone has a separate end switch in the panel, i would recheck your wiring and the manual i think you missed something, also what type of t stat for heat only uses 3 wires ? usually its 2, r and w

Tom_133

@newagedawn
many new tstats use 3 wire, nest, lyric, they use the green as a common for 24v. I was taught to never install 2 wire when running tstats alway 3 or more depending on application.

Mark Eatherton

He has Nest thermostats in his home. I've heard problems with the Nest due to the required third wire, and would have thought that most good control manufacturers would have gotten it figured out by now.

ME

kipper

@newagedawn @Mark Eatherton
Correct, I have Nest Thermostats that use the green for 24V common to keep the t-stat internal batteries charged. They consume more power than a normal t-stat given it's wifi & bluetooth with a touch screen. I have all the "smart" functionality disabled, and use the Nest at a set 67/68F year round.

I just installed the newly released Nest Temperature Sensor near my sofa in the living room to get another temp reading. You can prioritize the external sensor over the internal t-stat sensor, or use the external on a schedule. Right now Im just using it to gather information about the variances in temperature across my living room. Both the Nest and remote Sensor are in the same room, on the same Zone 1. See photo of Nest status below:

kipper

newagedawn said:

looks like your priority zone has a separate end switch in the panel, i would recheck your wiring and the manual i think you missed something, also what type of t stat for heat only uses 3 wires ? usually its 2, r and w

Per the Taco manual, the stand-alone Priority End switch is for "TT" ON BOILER WITH DHW "TT" INPUT. My boiler does not have a separate DHW input, Im guessing this allows you to run DHW calls at a different temperature than other heat zones.

The Taco manual also states:

The main end switch closes when any zone thermostat calls for heat and the mode switch is set to NORMAL. The main end switch also closes when the mode switch is set to RESET and a PC Series boiler reset power control is calling for heat. The priority end switch closes only when the priority zone thermostat or aquastat is calling for heat.

Im reading this to mean the Taco Main end switch opens for any call, so it wouldnt affect the cycling issue described here if I wired my boiler to both the Main and Priority end switches.

@Dave H
It would be nice if the Taco supported: when Non-Priority was calling and a Priority call started, the Taco would have a preset delay waiting for the Priority end switch, keep the boiler running, and switch off the other zones afterwards. If it didnt get an end switch update from Zone 1 after a preset delay, it would do it's normal routine of shutting off the boiler and waiting for Priority end switch. If this didnt occur during the Priority Protection period, the Taco would return to the other Zone calls.

Thoughts?

STEVEusaPA

kipper said:

Per the Taco manual, the stand-alone Priority End switch is for "TT" ON BOILER WITH DHW "TT" INPUT. My boiler does not have a separate DHW input, Im guessing this allows you to run DHW calls at a different temperature than other heat zones.

The Taco manual also states:

The main end switch closes when any zone thermostat calls for heat and the mode switch is set to NORMAL. The main end switch also closes when the mode switch is set to RESET and a PC Series boiler reset power control is calling for heat. The priority end switch closes only when the priority zone thermostat or aquastat is calling for heat.

Im reading this to mean the Taco Main end switch opens for any call, so it wouldnt affect the cycling issue described here if I wired my boiler to both the Main and Priority end switches. It would be nice if Priority and Non-Priority were calling simultaneously, it would keep the boiler running.

I think @ Dave H from Taco addressed that.

Did you try it with 'Priority' off?
Maybe you just need the ZVC406-4 and not the ZVC406-EXP-4

kipper

I think @ Dave H from Taco addressed that.

Did you try it with 'Priority' off?
Maybe you just need the ZVC406-4 and not the ZVC406-EXP-4

I disabled Priority for now, everything is working (switching DHW/Zone1 calls dont interrupt boiler). The only priority difference between ZVC406-4 and ZVC406-EXP-4 is the latter has the ability to disable Priority Protection, otherwise they both function the same (i believe).

ChasMan

No, same issue with the 404 non exp model. The issue is the delay between end switches. I would just parallel those end switches and try it. Well, I would confirm operation with an ohmmeter first but it can't hurt. And if it doesn't work, just run the zone valve from the setpoint directly and wire the end switch to the thermostat. Then you can jump the end switch in the taco. Where are your pumps wired?

kipper

ChasMan said:

run the zone valve from the setpoint directly and wire the end switch to the thermostat. Then you can jump the end switch in the taco.

I was trying to keep all the t-stats wired directly to the Taco for cleanliness, but this does seem like a good solution that would probably work.

ChasMan said:

Where are your pumps wired?

My boiler pump is wired directly to the boiler, my zone 1 pump is currently self-powered on 120v, and gets called by the endswitch of it's zone valve. See this thread for more info if interested, but long story short I recently installed a zone valve just upstream of the zone 1 pump because the DHW calls were heating the whole house!

hot_rod

> @Mark Eatherton said:
> He has Nest thermostats in his home. I've heard problems with the Nest due to the required third wire, and would have thought that most good control manufacturers would have gotten it figured out by now.
>
> ME
Caleffi relay boxes work fine with Nest, no pull down resistors needed. They have 3 end switches that can be configured several way

ChasMan

It will operate like this no matter what zone panel is used. He has to trigger priority with the zone valve end switch which kind of sucks. But he will get over it. In this case, I haven't had time to read the other thread but if he is happy with the pump operation as it is then the zone valve end switch and not the set point control should trigger priority to avoid restarting the boiler. Not as classy wiring wise for sure but otherwise you can't make use of the end switch safety and could deadhead the pump which I know some people don't care about.