Thermostat setup question

[Willyjp]

I have a gas fired boiler supplying hot water to an air handler (hydronic heat system) which provides forced air heating (and also a/c input from separate ac unit).  So ON SET UP:  should I use the “forced air gas” setting OR the radiant or radiators setting?? 

My existing Honeywell thermostat has the simple 4 wire connection ( red wire-power, green wire-fan, yellow wire-a/c, white wire-heat). (No C wire but I’ve got 24 volts ac across R—W) my existing thermostat has a screw setting for heat type (in for warm air, out 1 turn for hot water and was set for hot water). 

if I select radiant or radiator in the Nest, I lose the option of independent fan control.  But I’m more concerned about how the Nest will differ in handling the heat system.  It hears slower than forced air gas fired, but not much slower.  Much faster than any radiant system.  

So how should I set my Nest??

[Houptee · Accepted solution]

I would use forced air setting since you are heating with air not radiation so like you mentioned you need fan control. If you put radiation it will not turn on power to G fan when heat is required.

It will learn the system reaction time and will show when you change settings how long it will be to reach setpoint temp. Hence the name Learning thermostat.

[Houptee · Accepted solution]

I would use forced air setting since you are heating with air not radiation so like you mentioned you need fan control. If you put radiation it will not turn on power to G fan when heat is required.

It will learn the system reaction time and will show when you change settings how long it will be to reach setpoint temp. Hence the name Learning thermostat.

[Willyjp]

My understanding (tentative!) was that calling for heat or cooling automatically turned on the fan because the system was set up that way (external to the thermostat).  But you're certainly correct that I MUST have the fan when I'm heating, so forced air is definitely the way if the fan won't turn on with heating on a radiant/radiator setting.  I tried to get an answer to that question from Chat but it was a disaster......apparently the tech responding was only seeing SOME of my pasts!  Anyway, I appreciate your suggestion and I think I will use the force air setting.  What gave me doubts was that my existing (old) Honeywell generic thermostat had a screw-in/screw-out setting for forced air vs. hot water (which I suspect presumed radiant hot water) and it was set for hot water.  This is a new home (townhouse) to us, but he HVAC system is almost 20 yrs old!  Never dealt with a "hydronic" system before.  It is basically a hybrid of hot water & forced air.  So far it seems to be HIGHLY efficient as far as gas for heat and electricity of a/c, but most mainline HVAC people won't touch it with a 10 ft. pole!!  If anyone else out there has a Nest set up on a hydronic system, I'd love to hear from you!!

[Houptee]

Yes they are a rare type of system but they do work fine.

Now the trend is the new high efficiency inverter heat pumps that can produce heat down to outdoor temps into the teens or some close to 0F. 

Without seeing the wiring diagram of the system you have I would assume it needs the G to get power in a call for heat to turn on the fan, I could be wrong and it might have a wiring setup that if W has power on call for heat it internally turns on the fan.

You can try setting up the nest both ways and see how it reacts and if fan is not coming on when asking for heat, go back into settings and tell it forced air system.

[Willyjp]

Well, thinking it through, in my system, the White wire calls for heat from the air handler, which responds by turning on the hot water pump.  The Nest thermostat has no direct control over the heat source (large gas water heater), which just responds to its own thermostat when hot water starts flowing out and coming back cooled down.   So it seems logical that I should set it up as a forced air system, as far as the Nest is concerned.  With only 1 (white) wire,  all the Nest can do is call for heat, or not.  So the main difference, as far as the Nest is concerned, between a forced air setup where the G wire gets voltage too, or a radiant/radiator system where it does not, must only be in respect to the G wire also being on or off.  At least that would seem logical to me since the only option the thermostat can have is "on or off" to each of 3 wires.  I just now got the thing up and running, so I'm going to let it operate in forced air mode for a day or so.  Once I'm satisfied that it's running OK, I'll try it out in radiant mode to see if the fan comes on when I call for heat.  The reason I though it would, was that there was a step on the setup on the Google Home App (which I cannot seem to duplicate without starting the whole process over) where we can to the toggle between "activate" the fan, or not, when the heat comes on.  There was a little balloon that opened that said something about the Nest defaulting to activate unless NOT was chosen.  Now admittedly it was giving me that choice after I'd selected "forced air".  Maybe that step wouldn't even be there if I'd selected "radiant/radiator".  But I don't want to start the setup algorithm over.  I'll just let it be for awhile and then go in and change the system type, which I see that I can do.  Thank you so much for your interest and comments!

[EdwardT]

Hey folks,

@Houptee, thanks for the help!

@Willyjp, I'm glad to hear that Houptee's response answered your question. Please observe it for now and let us know if anything comes up.

Thanks,

Edward

[Houptee]

Let us know if it is working properly in forced air mode in case others have similar system and need help getting the Nest to work. Thanks!

[Willyjp]

It IS working quite satisfactorily in forced air mode.  Alternatively, I have observed that when heat or cooling comes on, the fan also starts in the "radiant/radiator" mode.  And the fact that such a "forced" turn on of the fan would occur in radiant mode was stated SOMEWHERE in all the copious Nest documentation that I read, though I can't find the specific line now.  

It stands to reason that such a forced turn on of the fan would be available with forced air heat at least, assuming that the air was being heated by local combustion.  If the fan didn't come on fairly soon, I would thing the firebox of a gas furnace would perhaps get dangerously hot!  Of course in my system, a call for heat only  causes hot water (close to 140 deg. F.)  to flow through the radiator coils in the air handler.  So failure of the fan to come on would just mean no distribution of the heat, but no local overheating.  

The warning that qualified that line I remember was that, in radiant mode, the fan function wouldn't be available as in independent option to turn on for a set time as it is with forced air mode.  At least that is how I remember reading it.  

What I'm really curious about though is what function, exactly, of my OLD conventional thermostat might be missing in the way the Nest operates.  I refer to the fact that my old Honeywell 4 wire thermostat had a setting on the back where a particular screw was direct to be "fully-in for forced air gas" and "1 turn-out for hot water boiler".  And my old thermostat was set on the latter setting.  I've thought a lot about that, and mused on it some in my prior posts.  With this classic 4 wire set up, basically you have one wire via which the thermostat calls for heat or does not.  So there can't be much subtlety to it!  The thermostat doesn't "know" if it's calling for hot air from a gas-fired furnace or hot water from a boiler feeding via pump to a radiator in the air handler.  EXCEPT that it knows "something" via that 1 turn difference in the "screw setting."  I have to think that MAYBE that screw setting has something to do with the TIMING of the thermostat's response, given that MAYBE gas-fire heated air is virtually instantly responsive to the call to provide heat or to stop, whereas the hot water pump to the radiator in the air handler is going to take a bit of time to push really hot water into the radiator in the air handler, and, when the pump stops, the hot water in the radiator is going to continue to provide heat for awhile until the now not flowing water in the hot water lines cools down.  

But, as I said, right now, in fairly mild heating conditions, the system seems to be working just fine.  When it gets a lot colder, later in the year, maybe I'll notice something about the way the heating system responds that will make me want to try the "radiant/radiator" setting on the Nest.  That difference in latency and persistence is mentioned in the Nest literature as the difference between the two types of heat.  

If perhaps someone out there knows more about thermostat programming than I do, you comments would be most welcome!!  

[EdwardT]

Hi Willyjp,

Thanks for the update. I'm glad to hear that it's working fine right now. I'm not familiar with how the Honeywell works but please let us know if you have questions with your Nest thermostat and we'd be glad to assist.

Thanks,

Edward

[Jeran]

Hey there Willyjp,

Do you have any more questions or need any additional help? 

Thank you,
Jeran
 

[Willyjp]

Well, since you ask, my original question was well answered, but  I DO have a NEW issue/problem with my new installation now approaching the end of its first month in service:  NEST OFFLINE W/O EXPLANATION

After running just fine for almost a month since install, my new Nest Thermostat was suddenly “OFFLINE”.  Could not address it with the Google Home App.  When first noticed, I was away from home for a couple of days.  On return, the Nest was still offline.  My internet was operating just fine, router App showed no history of any irregularity.  Interestingly, the router’s App on my phone showed the Nest “Online”, but the Google Home App showed it “Offline.”

When I approached the Nest, the display lit up briefly and then went black and seemingly wouldn’t come up again!  My first thought, since I don’t have a “C” wire, was that the batteries had discharged and I had no power to the Nest.  

I pulled the Nest off its base, checked the wire connection (fine) and popped the batteries out.  When I replaced the (original) batteries.  the Nest immediately re-started!  I placed it back on the base and it appeared to be operating normally!  While I was away, it was set to COOL to 76 deg.   With my returen, it auto re-set to COOL to 73 deg..  At that point, the temp reading was 76 (because I had just arrived) and the Nest showed cooling (and my a/c started up).  It cooled to 73 per schedule and showed normal operation now for 24 hrs.  

In other words, it appears that it HAD been working in my absence, even though my Google Home App showed if offline for the previous 2 days.  

I think what I did was “re-boot” it by removing and replacing the batteries.  After it re-started, going into the Settings/Batteries on the Nest showed (the original since install) batteries “Good” and a voltage of 3.18 v.  

GIven all the above, I’m at a loss to explain what happened that took my Nest Offline and, apparently, prevented it from re-establishing its connection to my wi-fi lan.  At first I thought, “Aha!  I have dead batteries.  I will need a “C” wire!”   But it turns out that my batteries were NOT dead, or apparently even low.

So what SHOULD I expect from the Nest:  if my wi-fi goes down due to a power outage (not necessarily what happened this time…not sure), will the Nest automatically re-establish its connection to the network?  Or will it have to be power-cycled/re-booted to get it to connect?

Any help, suggestions, information most appreciated!Well, since you ask, my original question was well answered, but  I DO have a NEW issue/problem with my new installation now approaching the end of its first month in service:

[Markjosephp]

Hi Willyjp,

I'm sorry for the late reply. I'd be happy to take a look into this for you.

Having the Nest thermostat (2020) often requires a C wire to work, though there are cases where it might not be needed.

Right now, the best thing to do is to install a Nest Power Connector or common wire. It could help provide constant power to your thermostat. Here are some references to help you install your Nest Power Connector on your HVAC system and on how C-wire works.

• Nest Power Connector installation article
• How to install the Nest Power Connector - video link
• Learn about the common or C wire.

Feel free to let us know if you have more questions in mind.

Best regards,

Mark

[Willyjp]

I appreciate the recommendation, and I am very aware of the possibility of needing a C wire.  However, my situation is a bit complicated in that my air handler, where the hydronic hot water feed and a/c compressor feed come together to provide heat/cooling, is in my crawl space!  It it completely out of reach to me (a very large but not obese 80 yr old who has the average lack of flexibility of my age!).  So to install a C wire, OR the Nest Power Connector, I will have to hire an HVAC contractor.  I've already talked to several, and they can "maybe get to this in a couple of months!"  

So, not to be arguing with your advice, but I'd like to focus just a bit more on the C wire power issue.  The three times (so far) that my Nest has gone offline, the battery status (once recovered) was "Good" per the Nest device.  Voltage reading was 3.18 v.  On one occasion, when I was fortunately present on-site, the Nest itself appeared to be working fine and I was able to get battery condition ("Good") and voltage readings (3.18 v) right off of the device, which my router reported as connected/online.  It was just that the Google Home App on my phone was reporting the Nest as offline.  But in actuality it appeared not to be!  

In all 3 cases so far, I've been able to re-establish the "online" condition in the App by power cycling my router (even though the router's connection table showed the Nest as online while the Google Home App showed it offline!)  And I've now discovered that I can view it's connected devices and power cycle my router remotely with its App.

The last event, occurring when I was remote, I successfully recovered the Nest to "online" status as shown in the Google Home App by power cycling my router remotely (the router's App showing the Nest online both before and after).

So in light of these observations, does it sound like lack of C wire power is what is causing my problem?  It seem to me that something else was going on here.  Certainly I haven't had to replace the batteries, or ever found them reported as less than "Good" when I check the Nest device directly.  And I've never seen the Nest report a voltage less than 3.18.  

If a C wire is what I have to have, I will gladly pay to have one installed, but the facts that I'm seeing, in light of the Nest literature I'm finding, just didn't suggest that was the problem.  

In just one other note: wi-fi signal strength does not seem to be a problem in that it always shows as "strong" on the Nest, which is only 15 ft. away from the router in the same space.  

[Markjosephp]

Hi Willyjp,

I'm sorry for the delayed response, and I thank you for your patience.

The Nest Thermostat (2020) often requires a C wire to work. In some cases, you might experience odd heating or cooling behaviors after installing your Nest Thermostat. Connecting the Nest Power Connector or a C wire to it may help resolve the issues.

In cases like those described in the articles shared above, the best solution is to contact a Nest Pro. The Nest Pro can diagnose and help fix any problems with your system and thermostat installation. If needed, they can also connect the power connector accessory to the Nest thermostat.

Feel free to let us know if you have more questions.

Regards,

Mark

[Markjosephp]

Hey there,

I wanted to see if you still needed help. Please let us know if you have any other questions or concerns.

Thanks,

Mark

[Willyjp]

Everything seems to be working fine except for the issue that occasionally (maybe 5 times total, twice in about the last month) the Nest seems to lose connection with it’s server (as reported on the Nest device itself; the Home phone App shows “Offline").  Even when the Home App is reporting the Nest “offline” my router can see it and it says it is connected to my network.  

The times I have observed it, I’ve always taken steps to correct it.  It’s possible that, left alone, the Nest would eventually reconnect with its server.  Its possible that very thing happens at times when I’ve never looked at the phone App to see that the Nest was offline.   But when I’ve observed it, it’s been at times when I was going to the App to make some kind of temp or program change.  

The Home App on my phone can’t see it at these times (shows “offline”), even though the router App on my phone concurrently shows that it IS connected to my wi-fi network.  This has probably occurred about 5 times total.  If I’m away, restarting my router remotely through its phone App has seemed to correct the problem, but it’s not something I’d like to do  too often because a remote restart takes about 10 minutes to fully re-establish everything in the house back online.   If I’m home, restarting the Nest from its Settings seems to take care of it.  

From comments I’ve dredged up on searching on this, it seems like at least a few others have had this issue.  It would be a real problem if it was frequent, but when it is only happening on rare occasion, it’s just a nuisance.  Observing the Nest when this has happened at home, it seems to be controlling the heating system just fine during this loss of server connection, even though it’s not connected to its server and the Home phone App can’t see or control it.  

The Nest is only about 15’ from my router in the same space, and no other connection issues have been observed with things in the house I have online, so it doesn’t seem to be a wi-fi connectivity issue.  

I don’t have a C wire, and can’t install one without some considerable expense and pro help because of the nature and location of my heating system (hydronic heat feeding an air handler in my crawl space!).  If that’s what it takes, I’d be willing to do that. But this issue of the Nest losing connection with it’s server does not seem to be a power issue because, invariably, when it occurs, the Nest battery condition shows as good and the voltage reading is always 3.17–3.18 volts.  The same set of batteries has served me for almost 3 months now and still reads as “Good” on the Nest.  So it doesn’t seem to me that lack of C wire power is the source of the problem.  

Maybe it’s just a WAN network gremlin, but any insight into this issue and how it might be avoided would be most appreciated!

[Markjosephp]

Hello Willyjp,

I appreciate your thoughts and your observations. Usually, it's likely that an unknown variable in your network environment (such as Wi-Fi network congestion, router firmware issues, or security settings) is causing it to disconnect from the Wi-Fi network and go offline. But I'd recommend examining your network environment to determine what the unknown variable could be and letting us know if the issue still persists.

Thanks,

Mark

[Markjosephp]

Hi there,

I'm checking back in — how's it going? Still need our help? Let us know so we can assist you right away.

Thanks,

Mark

[Willyjp]

I have been "Reply" responding to your emails.  But clearly that doesn't work because you are not seeing those replies.  So here is what I said in response to your 12/25 email:

I appreciate the answer. It requires some more examples to study…IF they occur.  But IS it really “offline” if ONLY the Google Home App says so??

Not to be overly repetitive, but every time this happens my router and the Nest itself say that it is strongly connected to my Wi-Fi LAN. It’s just that the Nest itself says it has lost its server connection.  To me that suggests something analogous to when one’s browser says it can’t connect to a given url.  I was thinking more along the lines of this being a problem between the App & the server??  A WAN problem rather than a LAN problem in other words.  Your support site has at least one or two other reports of similar nature. 

Anyway, hopefully it will be rare or non-occurring going forward. 

Thanks. 

WJP

[Markjosephp · Accepted solution]

Hello Willyjp,

Thank you for your patience, and I get your point. This happens due to an intermittent connection or bad reception, causing the thermostat to show offline in the app even if it's connected to the internet. For the time being, keep an eye on its behavior, and if the same problem persists, please let us know by starting a new thread, as we'll be closing this one in 24 hours.

Thanks,

Mark

[Willyjp]

Thank you Mark.  Yes, consider the thread answered/closed.   The problem described has been very infrequent and otherwise things are working fine.  If it starts up again, I will open a new thread.  Thank you.

WJP

[Markjosephp]

Hi there,

Thank you for your patience with us, @Willyjp. I'm glad to hear that it's been working well so far. Please don't hesitate to give us a shout if you have any further questions or concerns by creating a new thread, as we'll be locking this within 24 hours.

Best regards,

Mark