C wire & Aquastat L8148E

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  #1  
Old 11-30-18, 07:13 PM
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C wire & Aquastat L8148E

Hello everybody,

Like many people, I would like to use a smart thermostat with my old Burnham boiler and with my old Honeywell Aquastat. L8148E :-)

I have currently 2 wires connected to the thermostat and after reading some threads on this forum, I think I start to understand what I should do :

> The Tv is connected to the W of the thermostat (yellow on the pics)
> the T is connected to the RH of the thermostat (black on the pics)
> I have many other non used wires so I can use one of them for the C wire, and I think I have to connect it to the Z or W on the aquastat.

BUT i found this :
Thermostat/wire/aquastat
RH ---/---RED---/---TV
W----/--WHITE-/---T
C----/--OTHER-/---W or Z

AND as you can see the TV and T on my aquastat are inverted for the RH & W !!! So my questions are :

> what is the Risk of connecting the Z or W to the C Thermostat keeping Tv and T as it is ?
> Is there a risk to invert Tv and T ?
> I am far from being a expert, so doing all of this, if I mix up something, can I break something ?

I am adding pictures to help !

Thank you for your help

Alex
 
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  #2  
Old 11-30-18, 08:20 PM
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It does not matter how the aquastat is currently wired. You will change the wiring as you posted. I put the color wire I'd use after the terminals. This way it matches a standard. Turn boiler power off when changing the wiring.

RH ---/---RED---/---TV -------------> RED
W----/--WHITE-/---T ----------------> WHITE
C----/--OTHER-/---W or Z --------> BLACK
 
  #3  
Old 12-01-18, 08:01 AM
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thank you for your reply, pretty straightforward :-)

Just want to make sure : if I am mixing the wires, wilI I break something like the aquastat ? Or will it just not work ?

Alex
 
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Old 12-01-18, 08:08 AM
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You run the risk of damaging the aquastat transformer.
 
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Old 12-12-18, 05:54 PM
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Thank you.

Mu current thermostat is running on batteries and I will wait spring time to add a c-wire. So in case I break something it will not freeze for days at home 😁

Alex
 
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Old 12-12-18, 06:28 PM
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Good thinking. We'll be waiting for you come spring time. Name:  cool.gif
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  #7  
Old 03-02-19, 07:21 PM
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Lost!

Sorry to rehash this old thread but I kind of had the same issue.
i installed my Nest without a C-wire, just a W and Rh (white and red) and it worked fine. Heated when I asked to, turned off when I asked to. Only problem was there was a slight buzzing sound coming from the Nest when it went into heating mode. Almost sounds like faint relays clicking. It buzzes for about 5seconds then turns off.. 1 min later, buzzes another 5 seconds.. and repeats until the heat mode is off.
I read around and some people had the same issues. Most said that installing a C-wire fixed the buzzing.
So ok, I ran wire from my thermostat down to my furnace and since I have the same Aquastat model from this post, I hooked it up to the W terminal.
So far so good except on my Nest I now get an error that the C-wire doesn't have a constant 24v or it can't read the 24v feed.. furthermore the heat doesn't kick on anymore.
I pulled the C-wire from the Nest and it started working again albeit with the buzzing.
Question is why doesnt that W terminal on the Aquastat work? Do I need to remove the jumper between the W and Z?
Thanks
 
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Old 03-02-19, 08:42 PM
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Please read thru the thread carefully.
The connections between the aquastat and the thermostat are very important.

You must match this...........................
RH -----> TV
W-----> T
C----> W or Z

With two wires between the aquastat and the thermostat...... there is no polarity or connection preference. That changes completely with three wires.
 
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Old 03-03-19, 05:57 AM
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Thanks for the quick reply. Looks like I have some homework to do because both the TV and T terminals have a red and white wire connected to it. Finding out which is which will be quite the challenge in the rats nest of wires the previous owner left behind. Would I be able to just swap the W and Rh wires at the thermostat? I only ask because they put the water heater literally in front of the Aquastat and it's impossible to get to without laying over the furnace and working in reverse from above with a mirror! Took me an hour just to install the c wire!
The heating is 2 zones (upstairs and thermostat). Downstairs stat is only 2 wire (white and red)... Upstairs stat from what I can tell is 5 wire. I'm going to gather that the red and white go to the furnace and the other 3 are going to the AC unit in the attic. I will post a few pictures tomorrow and see if anyone can help me make heads or tails out of this.
Thank you so much again for the quick reply!
 
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Old 03-03-19, 09:21 AM
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Do you have a meter ?

At the stat end....... check from your new C wire to both of the old wires.
Only one will show 24vAC. That wire is R and the other is W.
 
  #11  
Old 03-03-19, 05:42 PM
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I don't, I'm a weekend DIYer with pretty limited tools however I will get one tomorrow while I'm out since that's always a good tool to have.
ill check the voltages and let you know. Again I'll most likely swap the Rh and W wires at the thermostat because getting to the Aquastat was damn near impossible.

I'll be swapping out the upstairs thermostat to a Nest in the coming weeks. Hope I don't have this problem up there!
 
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Old 03-03-19, 08:37 PM
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You don't need anything expensive or fancy unless that's what you want.
The home improvement stores carry analog meters starting around $15. That will work fine.
 
  #13  
Old 03-06-19, 05:28 PM
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So I bought a cheap Lowe's digital multimeter.. Woods model DMMW1.

Tested the C-wire to both the white and red wires and the results were less than satisfying..
Set the multimeter to 200v AC, put the com cable to the C-wire lead and put the V-cable to the white and red wires on the thermostat.
The white wire which I have in the W terminal on the Nest reads 0.0v.. the red wire which I have in the Rh terminal reads 26.4v

Also when I test the red and white wire against each other I also get 26.4v

Seems like I have them correct?
 
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Old 03-06-19, 05:41 PM
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Yes and yes.

Put the nest back in place and go to Settings---> Technical information---> Power---> Voc and Vin.
Tells us what you get.
 
  #15  
Old 03-06-19, 06:47 PM
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Without the C-wire installed:
Battery - 3.842v
Voc - 37.32v
Vin - 33.38v
Lin 40 mA (I)

With the C-wire installed: (I get error "E79" no power to common wire detected)
Battery - 3.794v
Voc - 2.46v
Vin - 2.46v
lin - 8 mA (I)





 
  #16  
Old 03-06-19, 07:06 PM
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Also to add to this.. at one point when I first put the C-wire last week the Lin read 200mA
 
  #17  
Old 03-06-19, 07:13 PM
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The problem is that the transformer in that aquastat is not able to run that thermostat directly.
It doesn't have enough output. It's even borderline on power stealing.
 
  #18  
Old 03-06-19, 07:25 PM
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Sooo just run the Nest without the C-wire?
it seems to run fine without it other that the intermittent buzzing noise when it goes to heating mode
 
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Old 03-06-19, 07:31 PM
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That's basically your best choice.

It probably buzzes when it gets low on charge.
You could consider adding a standalone 24vAC transformer to run the nest.
 
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Old 03-06-19, 07:46 PM
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Winter is almost over and the buzzing isn't crazy annoying. Just hoping that it doesn't prematurely break the Nest.
Plus my furnace is getting up there in age so we will be replacing that with a new one in the next year or 2. At least now I have new wires already run for a future new furnace.

A sincere thank you for all your time and help. Really appreciate it

 
  #21  
Old 03-06-19, 08:25 PM
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You stated that you have two thermostats and zones. Do you have zone valves? Normally there is an additional transformer as the Aquastat is not sized to drive valves or anything else support zoning. See if you can trace the wires coming from the thermostats and valves. It can be a complex job reverse engineering a system.
 
  #22  
Old 03-07-19, 04:31 AM
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Hi Astuff,

Yep, I have 2 thermostats (one for the upstairs and one for the downstairs that I know control 2 Taco valves at the furnace... I just moved into the house 2months ago so I am still learning everything but I also believe that the upstairs thermostat is the one that controls the AC unit in the attic which is one zone; only reasons I think this is because I don't see any other stat and the thermostat upstairs has 5 wires, (2) red, a green, a yellow, and a white) I have not yet bought a Nest to replace the upstairs stat.

To answer your question, yes I believe there is another transformer. Looks like line voltage goes into a junction box and the transformer is attached to the outside of that box.

As the thermostat wires come down from their respective thermostat they go into a rats nest of what looks like splice on splice on splice. Some continue to the transformer, some go to the zone valves, some go to the Aquastat and some go to the tank water heater (the furnace also heats up the domestic water tank)

Are you saying I could be able to pick up a C-wire to that transformer?
 
  #23  
Old 03-07-19, 05:42 AM
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With zone valves your system is different than the OPs so a different a solution is needed. Yes, pick up a C to that external transformer is what is needed.

Assume you have standard 3 wires going to each Taco zone valve and have standard wiring. See PJ's first wiring diagram at https://www.doityourself.com/forum/t...no-c-wire.html There are two wires at the transformer so you need to pick the correct one. Might be easier to pick up C from the center screw of any valve.
 
  #24  
Old 03-07-19, 02:36 PM
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Great, sounds like I might be back in the game!
i will take some pictures tonight.. the other transformer and the taco valves are waaayyy more accessible than the Aquastat so this is good news.
 
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Old 03-07-19, 06:27 PM
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I attached a couple of pictures of the 2 Taco zone valves as well as the transformer that goes with the valves.
Would I be able to tie my C-wire to the NEC terminal of this transformer? Or is it better to tie it into one of the ports on the Taco valve associated with the Nest thermostat?

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Last edited by PJmax; 03-07-19 at 07:10 PM. Reason: resized pictures
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Old 03-07-19, 07:13 PM
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Someone had a great time there with the three wire cable and loads of splices.

The #2 terminal on both valves is common.

Here's the problem...... you need to identify your correct cable from the thermostat.
Then you need to make sure the R and W is correct.

The W from the thermostat needs to go to #1 on the valve.
 
  #27  
Old 03-07-19, 07:20 PM
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You can tap it at either the transformer or the zone valve - doesn't matter which. Do a quick check and measure the ac voltage between each of the transformers two terminals and the center terminal of the zone valve. One should measure 0v and the other 24vac. The one that measures 0 should be C. The one that measures 24vac is R.
 
  #28  
Old 03-07-19, 07:46 PM
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Thanks again guys... I'll whip out the multimeter again tomorrow and do some testing.. might just do the c-wire connection at the transformer if it all checks out..

And yes, someone went splice crazy... It honestly looks more complicated than it should be.. will definitely look to clean that up in the future when it's time for a new furnace
 
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Old 03-07-19, 08:26 PM
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Don't forget to test at the thermostat location too after connecting the C wire.
You need to measure the 24v from R to C and 0v from W to C.
 
  #30  
Old 03-09-19, 01:38 PM
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Looking at my transformer picture. The ''load" terminal reads 0v when I connect it to the #2 terminal on my taco valve.
the "NEC" terminal reads 26v when I connect it to the #2 terminal on the taco valve.

​​​​​​On the taco valves if I measure #2 to #3 I get 24.7v.
if I measure #2 to #1 I get 0v

What I got out of this is I can connect my common wire to the "load" terminal on the transformer and run it up to my Nest.
Once I get to the thermostat I'll measure voltages against the C-wire to make sure the 24v guy goes in Rh.

Kinda funky though no? would have thought that the "NEC" would have been the common
 
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Old 03-09-19, 02:01 PM
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There is no labeling on the individual terminals.
That's not NEC it's SEC or secondary. Secondary and load are the same thing.

You should now put a C and R on the transformer for future reference,
 
  #32  
Old 03-11-19, 09:54 AM
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Gentleman,
1000 thank you very muches!

This looks like it worked. The Nest can read the common wire and the buzzing noise from the thermostat went away!

Really appreciate it guys
 
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Old 03-11-19, 07:16 PM
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Good job. Thanks for letting us know the outcome.

Rather than split the second members thread from the original thread..... they'll stay together.
If you need help with a job like this..... start a new thread and we'll be glad to help you.
Feel free to reference this thread in your new one.
 
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