Honeywell aquastat and nest thermostat problem (wiring)

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  #1  
Old 10-06-18, 11:10 AM
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Honeywell aquastat and nest thermostat problem (wiring)

my setup used to have dumb honeywell thermostats and i am trying to replace them with nest thermostats. It is a 2 wire Rh W1 setup. This is a instant heating radiant system with an aquastat and 3 honeywell zone valves (2 yellow and 2 red wires)

The current setup is a 24V transformer that is wired to the aquastat and then the aquastat is wired to the Rh terminals of all 3 thermostats. I replaced one of the thermostats and I get the error message "no power to Rh" wire after asking for heat for about 10 min likely because the aquastat is cutting off the power once the boiler has reached the temperature threshold.

My question is if I wire the thermostat Rh terminal directly into the 24v transformer instead of the aquastat, would that be a problem? I have attached 2 photos, one of my old setup and one of the new potential setup.


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Old 10-06-18, 02:36 PM
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Welcome to the forums.

I'm trying to figure out why the C line is shown as passing thru the L4080 aquastat. That does not look correct. If that's being used as a temperature controller it should be in the RR line from the valves to the boiler. When it reaches temp it opens the zone valve power which is not what is supposed to be happening.

I guess your second diagram will work for stat 1 but it should not have to wired like that..
 
  #3  
Old 10-06-18, 03:16 PM
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i have no idea since the builder set it up that way long ago. i spoke to the plumber that did the wiring and he's not very knowledgable

i'm guessing the 24v C power wire is connected to the aquastat to give the aquastat power? i spoke to an HVAC person and they're not sure why an aquastat was needed to begin with since the boiler is smart enough


it's also important to note that the boiler provides both instant hot water and radiant heat.
 
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Old 10-06-18, 04:14 PM
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i spoke to the plumber that did the wiring and he's not very knowledgable
That's terribly helpful.

L4080 is a generic model number. The letter and numbers following it determine its function. For the most part it's just a basic aquastat and does not need power. It may have been installed to not allow the zone valves to open without a high enough boiler water temperature.

It could possibly have been intended as some sort of high temperature safety cut-off but if that was the idea.... it's completely wired wrong.

I only install nest thermostats with a C connection. Members here have used zone valves to power the nest without a C connection with mixed results. It is highly recommended to get a C connection to it.
 
  #5  
Old 10-07-18, 10:54 AM
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I added a faststat common maker on thermostat 1 but the no power to Rh wire still existed in the old setup because I guess the aquastat was cutting off the power.

Therefore I was thinking of using the new setup method to remedy the problem and bypassing the aquastat and it seems to work ok.

i thought the old setup was odd because all the wiring diagrams online usually show the aquastat only wired to the boiler and never to the thermostats.


The the aquastat is a L4080 B1352
 
  #6  
Old 10-09-18, 01:36 AM
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I find that once I replaced the basic thermostats with a nest thermostat, the floors are a lot hotter.

I guess the old wiring diagram allowed the aquastat to cut off the thermostat power at a certain temperature so that the floors wouldn’t get that hot?
 
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Old 10-09-18, 11:01 PM
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Kind of silly but it is possible.
 
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