Trying to troubleshoot some Nest thermostats and 6 Zone Taco Box

D

DustyGmt

Member
Location
Vermont
New member as well as a new electrician, I finished my 4th year of electrical school a few years ago and am working on my own here and there and troubleshooting these kinds of things are not a strength. I guess ill just outline the problem as best I can.

Lady called and said she has 4 nest thermostats that arent working and the hydronic baseboard heaters arent coming on. First thing i did when I got here was pulled one of the dead nest T stats and plugged it into a micro USB to recharge it and then took a voltage reading on the Red and White wires, I was only getting 4V between the red and white at each of the 4 locations. I then went to the Taco box and tested the Line voltage and had 120v, then I tested each of the two transformers and was getting 27V, then I tested Zones 1-4 and was getting the 4V (no surprise) but Zone 6 which does the Hot Water Heater was reading out at 27V between the red and white and that is working properly. There are two transformers in this Taco Box and 2-5A Fuses and I tested those as well and they are working.

I then pulled all of the thermostats off the walls and went back to the taco box and started getting 9v on the red and white zones 1-4. I took the wires off zones 1-3 and was getting a reading of 13V on Zone 4. I apologize if this is scattershot, I'm certain my lack of experience troubleshooting Low Voltage controls is really showing here but just trying to walk you through my probably somewhat misguided process. Also turned the circuit off and put my meter on the Continuity Tone function and rang out each R/W Zones 1-6 and the only Zone having Continuity was Zone 6, the only Zone getting proper voltage and working properly.

Sorry for the giant wall of text, I'm out of my depth here and am ready to punt it to someone more qualified but its kind of eating at me that I cant figure this out, I want to become more skilled at troubleshooting these things but I'm inclined to believe that this may be a bad control box or maybe somewhere in this ugly rats nest of LowV wires there is a problem but it was working fine last winter so I'm not sure. Any tips or help from an old pro would be appreciated. Thanks. -Dusty
 
Not sure what's going on here. The terminal blocks on the bottom connect to the zone valves. 1&2 is the motor and 3&4 connects to the end switch. When the thermostat calls for heat, there should be 24VAC on 1&2. When the valve is all the way open the end switch closes "shorting" 3&4 which, through the Taco closes a relay and turns on the circulator through line voltage contacts marked "pump end switch" bottom left and also closes the low voltage contacts marked XX at the top left. XX would go to TT on the boiler which would control the circulator. Looks like this is the way it's done here.

The terminal blocks at the top connect to the thermostats. I see R&W which when "shorted" should activate that zone's zone valve as above. The "C" can be used to supply power to the thermostat instead of batteries.

Simple.

So, Check for 24VAC at the red and yellow from each of the two transformers.
Then check for 24VAC between R&C on each thermostat connector block.
If this checks out jumper R&W together on zone 1 and look for 24VAC between 1&2 on the zone 1 block at the bottom.

That should tell you if the controller is working properly. After that, expand your troubleshooting to the thermostat, thermostat wiring and zone valve wiring.

Here is a link to the Taco controller installation instructions.

https://www.tacocomfort.com/documents/FileLibrary/102-399.pdf

-Hal
 
Did it ever work with the nest thermostats ? How many VA is each nest thermostat 4?
The instructions @hbiss posted show the transformer A is 40VA and powers zone valves 1-3 so thats 12VA of load for the thermostats.

DustyGmt said:
Also turned the circuit off and put my meter on the Continuity Tone function and rang out each R/W Zones 1-6 and the only Zone having Continuity was Zone 6, the only Zone getting proper voltage and working properly.
Click to expand...
Smart thermostats should be wired with at least a 18/3 to deliver a 'common' for a 24 VAC power at the stat. Like pulling a neutral to a switch box. A old dumb thermostat can be on a two wire like a wall switch. Nest may send trickle thru the zone valve to work off a 2-wire not sure how reliable that would be or if Taco supports that.
You photo shows what looks to be 18/4 to the thermostats with only red and white connected I would connect the blue wire to the common terminal so between red and blue at the nest is 24 VAC.
I am guessing it worked fine with the old thermostats and the nest are unable to use whatever trickery to power its electronics by leaking current thru the zone valve.
Connect the blue wire to common and I bet they will work.
 
tortuga said:
Did it ever work with the nest thermostats ? How many VA is each nest thermostat 4?
The instructions @hbiss posted show the transformer A is 40VA and powers zone valves 1-3 so thats 12VA of load for the thermostats.
Click to expand...
Each thermostat only powers one zone valve, and zone valves are designed to be controlled directly by a thermostat. Not sure how the Taco controller works, are there relays that go between the thermostats and zone valves? So, you may be right about how the Nests are powered.

But you do make a valid point, did those Nest thermostats ever work? They are finicky and AFAIC not worth the trouble. Also, I question why the Taco controller was used. Normally a conventional thermostat just controls the zone valve directly. Thermostat turns on the motor/actuator and the end switch contacts close and turn on the boiler and circulator through the TT terminals on the boiler controller. Only use for that Taco controller is if the boiler didn't control the circulator, and I'm not seeing any evidence that the line voltage contacts are used.

I would probably get rid of the whole thing as well as the Nests.

-Hal
 
I found a Taco instructional video I saved from years ago. This one is on circulator and zone valve controls, just what we are talking about. Unfortunately, it's an mp4 video so I can't post it here. It seems that the only reason they used that zone valve controller is because it provides priority for the water heater. When the water heater aquastat calls, the controller shuts down any heating zone that may be calling until the hot water is satisfied or a time limit is reached. Depending on the size of the boiler, a cold start and all zones calling including the hot water would take a long time to reach temperature.

-Hal
 
hbiss said:
I found a Taco instructional video I saved from years ago. This one is on circulator and zone valve controls, just what we are talking about. Unfortunately, it's an mp4 video so I can't post it here. It seems that the only reason they used that zone valve controller is because it provides priority for the water heater. When the water heater aquastat calls, the controller shuts down any heating zone that may be calling until the hot water is satisfied or a time limit is reached. Depending on the size of the boiler, a cold start and all zones calling including the hot water would take a long time to reach temperature.

-Hal
Click to expand...
What is the voltage between terminal R and C at the taco zone control thermostat terminals, it should be 24 volts if not there is something wrong between transformer A and the R terminals, the thermostat should only provide a N/O dry contact, no power output. It looks like there are enough conductors in the thermostat cable to provide 24volts to power the thermostats so all the battery does is save the programming in the thermostat if the power goes out,
 
As an electrician for an hvac shop ( I am the one who gets to figure out why the controls on a new install dont work, aside from just "good old" electrical troubleshooting) I am going to throw a couple thoughts out here....... Knowing that the TACO controller has a bunch of electronics in it the voltages and currents at "R and W" man not what we are expecting.

My first line of testing would be to jump R and W at the stat(s)and see if things are working. If all is good, the issues lies with the stat. If this test fails, take the stat to the controller and connect it there with a short jumper. If this test passes, then it is a wiring issue wirh rhw cable from the TACO box to the stat location.

There is one thing that most of us dont know, the nest, and the ecobee ( as examples) use triac's to control the loads. These need specific ( i havent found the amount yet) current draws through them to operate properly.. The are are also VERY sensitive to overloads and shorts (found this out the hard way).

I do know for a fact that a Honeywell T6 PRO, and the internet connectable t6 PRO wifi have relays in them.

Hope this helps.


Howard
 
I confess I did not read the entire post but I also hang out on the "Heating Help.com" web site and Nest problems are very common. I have worked on a couple myself.

The NEST has a large battery and needs 24 volts to charge it. The 24 volt trickle to charge it when the stat is not calling does not work for very long and the battery will eventually go dead.

The consensus is that for heating you have to use constant 24 volt power to thee Nest and in some cases a separate 24 volt transformer and a relay.

My drawing is one way to do that and is attached. If you use a relay with a built in transformer the small transformer in the relay may not be enough to power the nest. be advised.
 

Attachments

  • RIB RELAY & TRANSFORMER FOR NEST.pdf
    91.7 KB · Views: 6
Eddie702 said:
My drawing is one way to do that and is attached. If you use a relay with a built in transformer the small transformer in the relay may not be enough to power the nest.
Click to expand...
No need for any of that insanity. If the Nest has a C terminal, just connect the C (with blue or black) to the C on the Taco. That's what it is there for. C is the other side of the transformer from R, should be 24VAC between them. If the Nest doesn't like that give it a new nest in the garbage can! I've not heard of one customer that had them being satisfied in the long run. Just a techi toy.

But, we're getting off track here blaming the thermostat. First determine that the control is working properly.

-Hal
 
hbiss said:
No need for any of that insanity. If the Nest has a C terminal, just connect the C (with blue or black) to the C on the Taco. That's what it is there for. C is the other side of the transformer from R, should be 24VAC between them. If the Nest doesn't like that give it a new nest in the garbage can! I've not heard of one customer that had them being satisfied in the long run. Just a techi toy.

But, we're getting off track here blaming the thermostat. First determine that the control is working properly.

-Hal
Click to expand...
I don't know what Taco relay he is using but most of those switching relays have small transformers that only have enough power to run the relays in the switching relay. They do not have enough power to recharge a Ecobee or Nest thermostat.

Its the same thing with oil burner primary controls. They have a small transformer. My Nephew installed his own nest and it worked for a year until the battery died. The Nest takes some power to charge. They were supposed to charge when the equipment is off because they would then have 24 v across W & R due to a small back feed. In most all cases this has proved not to work and they need a "C" wire and 24 volts across R & C to recharge.. When the battery gets low the Nest acts wonky.
 
Eddie702 said:
My Nephew installed his own nest and it worked for a year until the battery died. The Nest takes some power to charge. They were supposed to charge when the equipment is off because they would then have 24 v across W & R due to a small back feed. In most all cases this has proved not to work and they need a "C" wire and 24 volts across R & C to recharge..
Click to expand...
That's called "power robbing" and if it's unreliable to charge the battery it just goes to show the poor design. It's not like there are all kinds of control systems out there, it's always 24V in series with either a relay coil to turn on a circulator or the actuator of a zone valve. (Or power pile, but then forget it.) Not a tough thing to figure out. Seems to me that the C must be used, but that probably would make sales go way down because the majority of home thermostats do not use it and only 2 conductor wire is used. Probably the customers I heard of had experiences the same as your nephew and went back to conventional thermostats.

-Hal
 
hbiss said:
That's called "power robbing" and if it's unreliable to charge the battery it just goes to show the poor design. It's not like there are all kinds of control systems out there, it's always 24V in series with either a relay coil to turn on a circulator or the actuator of a zone valve. (Or power pile, but then forget it.) Not a tough thing to figure out. Seems to me that the C must be used, but that probably would make sales go way down because the majority of home thermostats do not use it and only 2 conductor wire is used. Probably the customers I heard of had experiences the same as your nephew and went back to conventional thermostats.

-Hal
Click to expand...
I used the rib relay and transformer (the drawing I posted) at my nephews' house and it's been fine for four years. I had no choice as his oil burner control had no "C" terminal. He ran his nest as a two wire for about a year until the battery finally died. I was in luck the two-wire cable pulled up to his stat actually was a 3 wire.
 
Oh I see right there on page 2 of the taco box under
Troubleshooting:
• Problem: Digital thermostats do not work cor-
rectly when connected to a zone valve control.
• Solution: Some thermostats are a “Power
Stealing” type which means they are powered by
the zone control with just 2 wires (R & W)....
Click to expand...
Yeah thermostat is closing a teeny tiny relay on the taco box not controlling the zone valve directly, so there is no 'load' for it to leak thru and rob its power like old wall timers and occupancy sensors did.
Hence the best solution is to connect the blue wires to 'common' bringing 24V to the stat.
 
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