Need some advice with boiler heat zone wiring - DHW priority wiring issue

[lml999]

Hearth fans may remember that we moved to Cape Cod in June, to a house with five hot water heat zones and a gas hot water heater. The hot water heater, recently installed, was too tall for the flue setup and was backdrafting.

So I had a local heating/plumbing firm replace it with an 80 gallon SuperStor indirect, fired off the boiler. (It has a second set of coils for solar heating, and I'm planning on adding a couple of solar collectors next spring).

This firm added a sixth heating zone to the boiler and installed a TACO control box to provide DHW priority -- when the SuperStor calls for heating, the hydronic zones shut off.

The issue is that the TACO box also shuts off power to my Nest thermostats and they don't like it. They pop up with error messages (no power on power line) and the batteries start to discharge. When the DHW priority is satisfied, power goes back on to the Nests and they usually clear the error.

Here's a link to the factory TACO box wiring diagram: (broken link removed to http://www.taco-hvac.com/uploads/FileLibrary/102-092.pdf)

At our old house, we had a fifty year old boiler with three zones and indirect DHW. Similar setup with DHW priority, unknown electronics. Never had this issue with the Nests. In that house, and this, the Nests are each connected by two wires. One way to address the issue is to run a separate power line to feed each Nest, but I've checked, and I've only got two wires to each thermostat. Running an additional line for power would be a huge PITA.

The right approach would be to use a control box that retains power to the thermostats even if DHW priority is being called. I don't know if the TACO box can handle this or if I need a different box.

The service provider has not been particularly helpful, and I'm a little frustrated. I'd like to go to them with a definitive solution to the issue...

Would appreciate your recommendations on how to move forward...

Thanks!

 

[fbelec]

take off the cover to the zone control. inside you should see a switch in the top right that says priority on or off. shut it off. you shouldn't need it. it only works better for over taxed boilers. the superstor should only take about 40,000 btu if piped correctly. you probably won't notice a difference. i have a 45 gallon superstor and it only takes 10 minutes to recover from a shower.

 

[maple1]

take off the cover to the zone control. inside you should see a switch in the top right that says priority on or off. shut it off. you shouldn't need it. it only works better for over taxed boilers. the superstor should only take about 40,000 btu if piped correctly. you probably won't notice a difference. i have a 45 gallon superstor and it only takes 10 minutes to recover from a shower.

My thoughts as well. Can't see needing DHW priority at all with 80 gallons of reserve.

 

[velvetfoot]

If the Nests were working okay without the indirect, I think they used an inappropriate control addition or miswired it.
If the original zone pump controller had 6 zones, it would likely have a priority switch on it.
It sounds like the controller they may have added, since you may not have 6 zones, might not be compatible with the original controller. Like an add-a-zone kind of thing.
Running a lot of thermostats with only 2 wires is tricky though, I've read.

 

[lml999]

If the Nests were working okay without the indirect, I think they used an inappropriate control addition or miswired it.
If the original zone pump controller had 6 zones, it would likely have a priority switch on it.
It sounds like the controller they may have added, since you may not have 6 zones, might not be compatible with the original controller. Like an add-a-zone kind of thing.
Running a lot of thermostats with only 2 wires is tricky though, I've read.

That's what I thought as well. The Nests are certainly able to work without a common wire...I used them that way for three years at our last house.

I talked to the TACO tech support. They said that they don't support the Nest without a common (third) wire.

Turning off priority is a thought...would be easier than running new wire to each of the thermostats. 4 of the five are pretty straightforward...the fifth will be a PITA...

Just picked up the last two Nests at Lowes yesterday, Had a couple of gift cards that I used for them, and for a new garage door opener. Did think about a compound miter saw, but....

 

[beardley]

Not sure what boiler you have, but I have the HTP superstor and an HTP boiler. When I had the system installed, the HVAC company put the DHW in the same zone controller as the heat zones, with priority. The problem I ran into with that, was the outdoor reset on the boiler was running the boiler at a lower temp than the set temp on the storage tank, so it would run endlessly.

This of course didn't become an issue for 6 months after the install once we got to warmer weather. Even though I could (and should) have called him back, I like to take care of things myself, and what I ended up doing was moving the DHW out of the zone controller, and back to the boilers main control board. Maybe an option for you, depending on the age/sophistication of your boiler.

 

[lml999]

So, to keep things afloat here, I turned off DHW priority. The Nests appreciated that.

Then I had a local electrician run 5 conduit wire to each of the Nests and provide the common feed from the TACO box.

Three of the Nests are now happy. Interestingly, two are still grumpy...they see the common wire but don't seem to be getting anything from it. These two are the furthest from the boiler. It just occurred to me that these are also the two newest ones, bought within the past 90 days. The other three are several years old, and were moved from our old house.

Unfortunately the bases are different on this version versus the three others, so swapping them around is a PITA. I don't know if it's a setting on the Nests or something else. Might give Nest another call...rather than moving bases...

 

[fbelec]

when you run the nest thru it's settings does the nest see the common wire? what happens does the nest go dead? i recently got called in to troubleshoot a nest not working right. the guy who installed the 3 nests for these people did not hook in a common wire which meant that once a week the thermostat had to be pulled off the wall and charged up with a phone charger. one of the nest tstat was bad out of the box. even with the common wire attached it would not charge so the customer called nest and they sent him out a new one.

 

[fbelec]

Not sure what boiler you have, but I have the HTP superstor and an HTP boiler. When I had the system installed, the HVAC company put the DHW in the same zone controller as the heat zones, with priority. The problem I ran into with that, was the outdoor reset on the boiler was running the boiler at a lower temp than the set temp on the storage tank, so it would run endlessly.

This of course didn't become an issue for 6 months after the install once we got to warmer weather. Even though I could (and should) have called him back, I like to take care of things myself, and what I ended up doing was moving the DHW out of the zone controller, and back to the boilers main control board. Maybe an option for you, depending on the age/sophistication of your boiler.

how new is your htp boiler? is it a wall hung? most boilers that have their own computer in them have to be wired with the dhw tank into the computer so that when the tank calls for heat the boiler will shoot for a 180 degree boiler temp and also disregard the warm weather shut down temp

 

[lml999]

when you run the nest thru it's settings does the nest see the common wire? what happens does the nest go dead? i recently got called in to troubleshoot a nest not working right. the guy who installed the 3 nests for these people did not hook in a common wire which meant that once a week the thermostat had to be pulled off the wall and charged up with a phone charger. one of the nest tstat was bad out of the box. even with the common wire attached it would not charge so the customer called nest and they sent him out a new one.

Yep, each of the Nests sees the common wire. Interestingly, the depression of the wire holder is what signals the presence of the common wire, not voltage on the wire.

The two (newer) upstairs Nests show the common wire but don't show the same voltage readings as the other three. Eventually, the two will go dead and I'll have to pull the common wire and let them recharge via the two wire (power stealing) setup.

I'm going to get on the phone with Nest to see if there's a setting I can change.

I should also swap one of the (older) downstairs Nests for one of the upstairs ones just to see if the problem follows the (newer) Nests. As I mentioned previously, the mount is just slightly different so I need to swap both the mount and the Nest itself...

 

[beardley]

how new is your htp boiler? is it a wall hung? most boilers that have their own computer in them have to be wired with the dhw tank into the computer so that when the tank calls for heat the boiler will shoot for a 180 degree boiler temp and also disregard the warm weather shut down temp

Yea, what you're describing is exactly how I have it wired now. When I had it installed about a year and 1/2 ago, they put the DHW in the external Argo zone control box. Depending on the age of Mr. lml999's boiler, this could be a potential solution as well.

I currently have 2 nests attached to the Argo, with only 2 wire, no common, and they've worked flawlessly for that year and half, even when set to "off" for the summer.

 

[fbelec]

Yep, each of the Nests sees the common wire. Interestingly, the depression of the wire holder is what signals the presence of the common wire, not voltage on the wire.

The two (newer) upstairs Nests show the common wire but don't show the same voltage readings as the other three. Eventually, the two will go dead and I'll have to pull the common wire and let them recharge via the two wire (power stealing) setup.

I'm going to get on the phone with Nest to see if there's a setting I can change.

I should also swap one of the (older) downstairs Nests for one of the upstairs ones just to see if the problem follows the (newer) Nests. As I mentioned previously, the mount is just slightly different so I need to swap both the mount and the Nest itself...

run a volt meter from the red to the common and you should get around 24 volts if not that is your problem. if you get 24 volt ac at those terminals then a call to nest is in order. i had one bad out of the box also at the customers home.

 

[fbelec]

Yea, what you're describing is exactly how I have it wired now. When I had it installed about a year and 1/2 ago, they put the DHW in the external Argo zone control box. Depending on the age of Mr. lml999's boiler, this could be a potential solution as well.

I currently have 2 nests attached to the Argo, with only 2 wire, no common, and they've worked flawlessly for that year and half, even when set to "off" for the summer.

depending on the control if using in current robbing mode sometimes a resistor has to be install. glad yours is working well. from what i'm told nest works better 2nd year into it.

 

[lml999]

run a volt meter from the red to the common and you should get around 24 volts if not that is your problem. if you get 24 volt ac at those terminals then a call to nest is in order. i had one bad out of the box also at the customers home.

Thanks, will do. Seems mine has gone missing in the move, I'll pick up a new one.

In the meantime, I swapped two of the Nests around. The older Nest, which is working fine downstairs, reported no power on RH just as the new one does. Looks like I've probably got a wiring issue. Too many shortcuts have been taken in this house, and the guy that ran the new wire for the thermostats upstairs only used the white common wire. Guess he didn't want to mess with the existing wire...but whatever, it's not working.

Speaking of shortcuts, the previous owner finished the basement of our house a couple of years ago and I can't find a shutoff for an outside faucet. D'oh. Had a plumber come in, cut a nice hole in the finished wall, install a frost-safe outside faucet and an inside shut off valve....

 

[lml999]

run a volt meter from the red to the common and you should get around 24 volts if not that is your problem. if you get 24 volt ac at those terminals then a call to nest is in order. i had one bad out of the box also at the customers home.

Great suggestion. I checked one of the two in question. No voltage between red & common. Looks like it's a wiring issue...

 

[fbelec]

hopefully you have a spare in the group of wires. i've seen the wires break at where they come out of the sheath they are bundled in. check the cable it self to see if it looks like the same as the cable at the boiler. i can't even count the times i found a splice and a bad wire at that splice. once you get voltage at the red and common you are home.

 

[lml999]

hopefully you have a spare in the group of wires. i've seen the wires break at where they come out of the sheath they are bundled in. check the cable it self to see if it looks like the same as the cable at the boiler. i can't even count the times i found a splice and a bad wire at that splice. once you get voltage at the red and common you are home.

When I had the gas hot water heater replaced with an indirect and added the TACO box, the installer created a bit of a rats nest of wiring. Also, as I found out last week, the installer didn't run a proper feed to the indirect, just created another zone. So I'm heating the 80 gallon SuperStor with an undersized zone. Jerks. I paid them for a proper installation, and they mentioned something about two options, but didn't explain to me the details. They just didn't want to do the extra work to do it right.

Hasn't been an issue for us so far...we've had plenty of hot water, but when we replace the boiler, we'll set it up properly. Not sure it's worth reworking in the interim. The boiler is 22 years old and seems to be working fine.

The guy that pointed this out will rewire the TACO box, getting rid of the rats nest. He seems to have a clue.

 

[fbelec]

that's the name of the game having a clue. most plumbers can wire them but don't because it takes them to long and don't now control wise what's right and wrong. most electrician's can power them up but the rest of the wiring is done blind. i'm fortunate enough to know it well including the computerized set ups. i troubleshoot them when the other guy can't figure it out. if your guy piped in your tank with half inch pipe it will work fine but will take just a few more minutes to come up to temp that's all. it should be done in 1 inch pipe. i have a htp superstore 45 gallon tank the time it takes for one to shut off the shower towel off and get out the tank is up to temp for the next shower.

 

[lml999]

The guy that pointed this out will rewire the TACO box, getting rid of the rats nest. He seems to have a clue.

Confirmed. He has a clue. In a few short hours, he removed the rats nest and wired the five Nest thermostats to talk with the TACO box. He used the new five conduit wiring run by another guy (retired electrician, somewhat out of his league) and each of the Nests is now reporting proper wiring and power.

We can close the chapter on this one.