Nest Lacks Power - Ready to Use a Relay... Will This Work?


  #1  
Old 12-28-14, 08:28 PM
F
Member
Thread Starter
Join Date: Dec 2014
Location: USA
Posts: 2
Received 0 Votes on 0 Posts
Nest Lacks Power - Ready to Use a Relay... Will This Work?

Hello all,

Will try to make a long story short. I have heat and AC. Two Nest thermostats. One works great - and it's connected to both heat and AC. The other Nest is consistently low on power, and it only operates heat (Lochinvar Knight boiler). As a result, I've needed to take it off WiFi in order to maintain it being on... thus defeating the purpose of getting a WiFi thermostat! So, what to do...

The good news is that I have 3 wires in the thermostat line (R, W and C). The bad news is that C is not connected to anything - just hanging back in the wall. The installer didn't hook it up, and frankly I had no idea either. In a perfect world, I could just hook up the C wire to the C terminal on the boiler and from what I've read all over the internet, that should give it the juice needed. But I'm not savvy with electronics etc., so opening up a new high tech boiler and fumbling around for this C terminal doesn't sound great to me.

So, question #1: Does anyone know if the Lochinvar Knight high efficiency boiler has this type of C terminal, and if merely hooking up that wire would work? If so, is this better left to a pro? Or could a novice like me do it? Where is it, and how would I get to it?

Back to my story... my second idea, and one I was about to embark on, was to re-wire with 18/5 thermostat wire and then just hook up a 24vac transformer across C and Rc as it's own circuit. It was a good idea until I realized the dang 3 wire thermostat line already there is stapled behind the wall, and thus I cannot fish it out (while fishing new line). And I'm not about to break open walls etc for a new line...

So, after researching a bunch more, I ended up with a new plan that I think will work, but wanted to run by folks here to see if this truly would work or not. I've purchased a 24V transformer, and a SPST relay. My plan is to hook it up using the diagram provided by hvactechfw (message #13) in the post here: http://www.doityourself.com/forum/th...ansformer.html

Leading me to my final question:

Question #2: Would this wiring scheme work you think? Is there any risk of adding this 24v transformer to the same relay that the boiler is on? I'm not an electrician, so not sure if the boiler circuit would be in trouble with this other 24v, or does the relay block that - or doesn't it matter? Just don't want to fry anything obviously!

Thanks everyone!
fade6
 
  #2  
Old 12-28-14, 08:56 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,425
Received 17 Votes on 14 Posts
http://lochinvar.com/_linefiles/KBXII-I-O-Rev%20G.pdf

You can add a relay and transformer or install a fan center.

7 and 8 would be the 2 wires to the boiler from the old stat.




Is this your boiler?

Name:  Lochnivar.jpg
Views: 1959
Size:  49.7 KB
 
  #3  
Old 12-28-14, 09:13 PM
F
Member
Thread Starter
Join Date: Dec 2014
Location: USA
Posts: 2
Received 0 Votes on 0 Posts
Thanks Houston! Yes, that is my boiler. So if I understand correctly, I can either: add the SPST relay and 24v transformer as shown in the diagram I linked, or install a fan center via the diagram you showed? Please confirm - either will work?

Thanks a ton! I'll look into this. Appreciate it, and the quick response!
 
  #4  
Old 12-28-14, 09:15 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,425
Received 17 Votes on 14 Posts
Yes, either way will work.

Name:  Nest with boiler.jpg
Views: 7108
Size:  37.0 KB


A fan center is only a fan relay and a transformer mounted on a 4 by 4 plate for easier mounting on a 4 by 4 junction box.
 

Last edited by Houston204; 12-28-14 at 09:45 PM.
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: