Nest issues with dual systems
Comments
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Modulating condensing boiler. These should be set up with an outdoor sensor which lets the boiler adjust water temperature based on outside conditions. The idea is to make water only hot enough to provide just enough heat for space.
Yes, extend the resistor with 18 gauge wire back to the COM terminal. Start with one resistor for each Nest and see how it runs.
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Nest has had sub base issues since they first came out.
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The Honeywell 8000 series thermostats uses relays. It is powered from the Rc (to C) terminal, there's a physical wire jumper from Rh to Rc that needs to be removed for dual transformers.
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Let's try this again. These thermostats — particularly WiFi ones — need a LOT of power to operate (the horrible old fashioned ones didn't need any…). That power is intended to be provided by 24 volts AC between Rh and Rc and C. If there are dual systems — for instance an air conditioner and a boiler — then one system will power Rh and C and the other Rc and C. If there is only one power supply, then you need a jumper between Rh and Rc to power both sides of the pesky little critter.
Now when the thermostat calls for air conditioning or fan on or first stage heat or second stage heat it makes a connection — internally — from Rh or Rc to W or W1 or Y or G or whatever, and that connection then runs to the relay (which may or not be solid state) or contactor on the controlled device and thence back to the common on the respective power supply.
For better or worse, there is no standard for exactly what those control wires are connected to on the control device. It could be anything from a very high impedance Triac or similar device — or it could be (and usually is, with hot water and steam systems) a very low impedance device. The Nest, in particular, assumes a very high impedance (the people who designed it never heard of a "relay" never mind a "contactor").
The way around it is simple. Power the Nest or similar gadget from an independent 24 volt AC supply. That will keep it's tiny brain from having a stroke. Then hook up a relay with a 24 volt AC coil from the appropriate control wire back to the common of the same power supply.
Then use the contacts (one would usually use the normally open contacts of the relay) as a simple closure to tell the controlled device to turn on.
No problems with phasing power supplies. No problems with trying to steal enough power to keep the Nest operating. No problems with complex wiring. What's not to like?
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
You don't trust a Honeywell thermostat to not have a crap ton of exploits but you want to use a Nest?! This has to be the funniest thing I've heard in a long time 🤣. Honeywell has been making great thermostats longer than almost all of us have been alive, but Nest is great because it's popular? Lol, it's only popular because it's heavily marketed and people falsely believe that it has some magic beneficial aspects that will make their system work better, when in fact it's quite the opposite.
If only everything that was popular and trendy was actually good…
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Jamie,
You are correct. Wifi thermostats do need a lot of power. In case of the Nest it takes this from the Rc and C connections to the AC unit.
The only power it needs from the heat side is to run the local electronics that monitor and control W1. This power it steals from the Rh and W terminals which is why it can sometimes turn on the heat.
By adding the resistor to the Taco box, it can now source more power to the W terminal so it won't accidently trigger the heating zone.
Now I don't know if this will fix the OP's problem, but an easy thing to try.
I do agree, simpler is better. All my thermostats are simple setpoint units, don't even bother with setbacks.
I do enjoy a wifi thermostat at the cottage, being able to turn up the heat so it is nice and cozy when you get there. Sometimes it is worth the complications.
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I'm not discounting Honeywell and I'm sure they make very good hardware. But a smart thermostat requires an app, it requires backend services, it requires load balancing, authentication, security, fail over etc. You know, the kind of stuff that a *software* company does. Sadly, Honeywell is not a software company and it very much shows. Just search the app store or Play Store for Honeywell apps - all garbage with 1* or 2* ratings. They may have been making Thermostats before we were born, but they sure as hell don't know how to write software.
So I guess pick your poison? I'll take the better software if I can fix my problem with a $20 relay.
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There is a setup that the Rh and the Rc on the NEST is very comfortable with. The central AC that uses R, Y, G, and C and a single zone boiler with an analogue control (like Honeywell L8124 or L8148 controls that will use the Rh and W. There are no electronic parts in those controls. The problem with the setup that you have is, that your boiler side is using a more sophisticated Taco SR500 series control that may have tiny little bits of electronic chips that want the dry contacts of an analog thermostat.
If you have no problem with spending extra money to use 3 or 4 new thermostats to avoid the cost of two relays, then the Ecobee is the right thermostat for you. I assume that you want one smartphone app for all the thermostats, so that means that all the thermostats need to be able to talk to the same app. There is no app I know of that both the NEST and the Ecobee can talk to without interconnection software issues. Maybe Google or Alexa smart house apps can do that for you, but do they do all the tracking and energy use calculations you want? NO! You have NEST and Ecobee apps that you have to manually add together to get your real totals.
Rib relays don't need an app and two of them are less expensive than 3 or 4 new thermostats. But I get it. If something is hard for me to understand and there is something that I believe will be easier for me to handle myself, I will sometimes throw out the perfectly good gadget and spend thousands of dollars on the one that I can understand. I did that with my doorbell camera. Got 6 new cameras in my home because I couldn't get my doorbell camera to connect to my wifi network. I ended up getting a new internet service provider and new cameras just to get a doorbell camera that I could program myself.
After it was all done, the installer of the fiber optic connection to my home set up a way that my old doorbell camera could be connected to the new Wifi network. Thousands of dollars later, I have the old doorbell camera on my back door now. All because I could not figure out how to get a 2.4 GHz camera to work on my 5.0 GHz wifi. Seems that the old modem has the capability but always defaulted to the 5.0 because both bands had the same name and password. When the doorbell camera stopped working one day, I couldn't reconnect it. And no amount of technical support on the phone with Comcast and Ring was ever going to get it to work. I don't speak that tech jargon language.
I'm sorry that my diagrams and explanations were unable to persuade you to throw away $60.00 for a chance to get your existing thermostats to work. I guess I'm just not that good of a persuader.
Good luck with your new thermostats.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Ed, I actually installed one relay last night and it's working like a charm. I didn't get a chance to thank you yet, so thank you :)
I went ahead and ordered the 2nd relay now that I confirmed this working.
Btw, I still don't understand how the analog inputs on the Taco are different from analog inputs on single zone broiler. That's too complex for me to process :)
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No, I agree that Honeywell/Resideo is not a software company. Nor do they intend to be.
And once one starts up the garden path of apps and software and what have you, that's all very fine — if it all works.
Someone a few years back quipped that if cars had the reliability of software, we'd never make it to the grocery store. Sadly, that's the way cars are going. While the machinery itself may be going strong at 500,000 miles, the various computers and what have you, never mind the 'phone app, failed 400,000 miles ago and the updates and patches are no longer available, never mind replacement parts.
One may sound the praises of fancy apps and software all you like, but it will all be junk in 5 to 10 years and you'll need all new (and fancier and more expensive and more invasive) stuff.
Nope.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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To complicate it even more, different vintages of the Nest thermostats behave differently. Possibly to make them more user/ system friendly? Some work fine with the Caleffi relay boxes, some not so well.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Its hit or miss with them. I don't like the one's that look like an art deco bowl mounted vertically with the mirror finish. Finding the right place to tap it is like trying to... ah, never mind.
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And here it is in pictures. Don't mock my wiring skills lol. But constructive feedback accepted.
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Won't knock the wiring. We've seen much much worse…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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They are not different…. the NEST inputs are different form the contact type thermostats. I believe that Ecobee uses contacts that click. My Amazon smart thermostat clicks. You will never heat a click from a NEST thermostat because of that weird virtual switch.
The receiver of the analog contact switch and the virtual switch are what the difference is for the NEST. The zone control you have has more than just a transformer and a relay coil in the thermostat circuit.
The left control internal diagram shows no electronic junk. The thermostat circuit consists of three things. Transformer (source), relay coil (load), and the thermostat contacts (return path). Only Taco knows what is in that circuit for the individual zone thermostat circuit(s). No internal circuit diagrams are published for public use.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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@backshift_dividers said: And here it is in pictures. Don't mock my wiring skills lol. But constructive feedback accepted
I have seen where the RIB is connected with the 1/2" electric knock out directly on the SR500 box and the extra wires are hidden behind the box cover. Otherwise relay that makes it work so there you go!
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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How come the relay isn't needed when I use a heat-only Nest thermostat? Wow I just can't get my head around this. Like, if there were compatibility issues between Nest and Taco, then a relay would always be needed. Interesting stuff.
Btw, can anyone identify what the other electronics board sitting on top of the frame is? I think it's connected to the isolated end switch. Seems like an odd location lol.
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You are using the transformer in the Taco SR506 to power that thermostat and you are probably connected to RC and W and C. For some reason the use of the Rh on the NEST is the problem with the SR506. When you use the Rc on the NEST and draw the power from the SR506 the problem goes away. You are using only one transformer to operate the NEST in both cases. Air handler transformer for the AC system with the Heat relay. SR506 transformer for the heat only thermostat.
It is that 2 transformer thing that is the problem. When you go to one transformer the problems goes away.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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