High Voltage Thermostat switch to Low Voltage Thermostat w/water baseboard heat?

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Old 03-01-08, 05:58 AM
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Exclamation High Voltage Thermostat switch to Low Voltage Thermostat w/water baseboard heat?

Hello All,

Thanks for the help in advance. I currently have three zones in my house for hot water baseboard heating. 2 of the three are already low voltage thermostats. The last one is a high voltage (which I didn't realize till I went to replace the thermostat). I traced it back to a older Honeywell relay that controls the pump.

My question is how can I switch this to a low voltage thermostat? I thought the best way would be to replace the relay box (I am not sure if thats the proper term).

I already ran a low voltage wire from the relay box to where I want to put the new low voltage thermostat. (ran two actually, because one will control a central air unit that will be going in once we have some $$)

Any and all help is appreciated. This is my first time posting on this forum, but I maintain an active blog about my house activities / renovation here if you interested: http://burm.net

Also, just curious on the Relay the Brown wire is going to the actual boiler, what does that wire do / tell the boiler? Does it tell it to fire up?

Thermostat:

Relay thing:

Thank you,
- John
Http://Burm.net - My Renovation Blog
 

Last edited by burmjohn; 03-01-08 at 06:04 AM. Reason: fix spelling
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Old 03-01-08, 06:05 AM
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Thermostat replacement

Sounds like you have a master/slave thermostat setup did the other stats have anything to do with the pump and boiler or do they just open and close valves?
 
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Old 03-01-08, 06:14 AM
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Originally Posted by mike n View Post
Sounds like you have a master/slave thermostat setup did the other stats have anything to do with the pump and boiler or do they just open and close valves?
How can I check? Should I take a pic of the other thermostat relays?

Thanks
 
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Old 03-01-08, 06:29 AM
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To answer your question you now can add a 24v thermostat. If this is normal boiler and control wiring I would change the wiring a little. The thermostat wire where you have two red wires, cut that and put red & white on the terminals. This control will supply 24v to the thermostat. Run a wire from terminals 5 & 6 to T-T (another power source) on the boiler control. When 5 & 6 closes it will fire the boiler. You have two power sources this way if that wire from the thermostat to this control continues to T-T on the boiler aquastat.
 
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Old 03-01-08, 07:05 AM
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WOW - I need to digest this. On the first 4 passes i'm confused.

Where you say "The thermostat wire where you have two red wires, cut that" - Is that the T T Wire you are referring to? Does that mean T is 24v?

What do you mean if this is normal boiler wiring? How can I tell? By Boiler control you mean (in my terms) the relay box?

Sorry I need more clarification, i'm a plumbing wiring newb!

Thank you
 
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Old 03-01-08, 07:11 AM
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Originally Posted by mike n View Post
Sounds like you have a master/slave thermostat setup did the other stats have anything to do with the pump and boiler or do they just open and close valves?
Mike - the other two thermostats fire the other two pumps (zones) - I hear the boiler kick on all the time when the other pumps kick on.
 
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Old 03-01-08, 09:01 AM
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Hang on a sec ...

That red wire on the 845 relay : That's just a JUMPER between the T - T connections, right ?

And the brown wire goes to the boiler to fire it up ... IF it's coming from 5 & 6 on the 845 and continuing to the T T terminals on the boiler.

Show us where that brown wire connects to the boiler.

What I believe your line voltage thermostat is doing is switching the 120 VAC that powers the 845 relay.

You can check this by putting a voltmeter that is set for 120VAC (or a test light) on the L1 and L2 terminals on the relay box, and cycling the thermostat. BE CAREFUL! 120 VAC present ! If the power to L1 and L2 goes on and off with the thermostat, then that's how it's wired.

If you remove the red***(see note below!) jumper, wire your new tstat across the TT terminals and provide a constant source of 120 VAC to the relay box, it would work exactly the same as before.

*** NOT the red jumper between terminals 1 and 4 on the relay, that one must stay and NOT be connected to the new thermostat.
 
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Old 03-01-08, 09:28 AM
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Originally Posted by NJ Trooper View Post
Hang on a sec ...

That red wire on the 845 relay : That's just a JUMPER between the T - T connections, right ?
Yes it looks like it, it doesnt go anywhere else. How do you know that is 24 V? Is that what is standard?

What does the T stand for anyways, and whats the point of the jumper?

Thanks guys, I really really appreciate the help!!!
 
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Old 03-01-08, 09:49 AM
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I'd still like to see where the brown wire goes on the boiler if ya don't mind. Just wanna be sure what I'm telling you is 100% correct!

The T-T connections are Thermostat.

Yes, 24 VAC... that silver cube in the 845 relay box is a transformer that takes the 120 down to 24.

There's hundreds of ways that these relay boxes can be used. The original installer opted to keep the existing line voltage relay in place, and instead jumpered the TT terminals on the 845 so that when the 120 came in from the thermostat, the relay would close and fire the boiler, and run the circulator (which by the way is wired from 2 to 3 on the 845, yes ?).

If ya wanna 'play' a little bit, remove the jumper between T T in the 845. Turn up the line voltage thermostat until it's calling for heat. The relay will NOT pull in with the TT jumper removed. With the thermostat still calling for heat, touch the jumper back on the TT terminals. The relay will pull in, and the boiler/circ will run. If you wish to further verify what I'm tellin' ya, take your voltmeter and measure between T T with the jumper removed. 24 VAC (nominal) is what you will see there.

By providing constant 120VAC to 1 and 2, and wiring the new thermostat between T and T , your system will operate exactly as it did previously, except with a low voltage thermostat controlling the relay.
 
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Old 03-01-08, 12:06 PM
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Looking at the picture it looks like the brown outer jacket of the wire was slit open and the red wire was cut and put on the two T-T terminals.
 
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Old 03-01-08, 12:44 PM
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I took a few more pics.

This is where the brown wire goes - This is the "relay" for the first floor which is on 24v.

Huge pic here: http://www.flickr.com/photos/burmjoh...16836/sizes/o/



Then it heads over to the relay for the 3rd zone (i think!). Not sure where it goes after that (to the aquastat as you mentioned before??)

HUGE image here: http://www.flickr.com/photos/burmjoh...16764/sizes/l/

 

Last edited by burmjohn; 03-01-08 at 04:28 PM.
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Old 03-01-08, 03:15 PM
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OK, so from what I can see, it looks like the brown wire (red and white leads) goes from terminals 5 & 6 , then jumps to 5 & 6 on the next relay... so on 5 and 6 on that relay, you've got two reds on one, two whites on one, and the next relay in line is the same. Then, those last two red and whites are going to the yellow wire nuts on the front of the boiler ?

See how the thermostat is wired to that next relay terminals T T ? and notice that the 120VAC into that second relay is always hot ?

I can't tell if there's a jumper between 1 and 4 in the second relay box, is there ?

You are basically going to duplicate the conditions at that second relay box in the first one.

sent ya a PM, off-topic ...
 
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Old 03-01-08, 06:49 PM
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4 and 1 are jumped and have black on both relays.

3 has a red on the working 24v and 3 on the 120 VAC has black?

The red on the 120VAC is cut, not doing anything.

Whats the red doing / going on the 24v one?

I touched 1 & 2 together and nothing fired, actually i tested the voltage on every screw in there, it seems they are all dead then the thermostat is off. (all live when its on!)

I also verified that on the 120 VAC with the thermostat cranked, the T-T disconnected shuts it off and touched turns it on.

Sorry
 

Last edited by burmjohn; 03-01-08 at 07:11 PM.
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Old 03-01-08, 07:40 PM
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NO! don't touch 1 and 2 together under any circumstances! That could be like sticking a paper clip in a live outlet !

Luckily for you, it seems as though if you touched them together you did so when the thermostat was OFF ... if you had done that when the thermostat was calling for heat, you woulda got a big BANG! SPARK! and likely would have hurt yerself, and fried the thermostat ... and the relay, and yourself ... please don't do that anymore !

I need to look at the pics again ... do you have a red black white and ground coming in on that box ?
 
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Old 03-01-08, 08:10 PM
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John, on relay #2 , the one on the boiler (blue background), I see one cable coming in, with a WHITE , BLACK and RED . I see the white going to term 2, the black going to term 1, and the red going to term 3. You said there is a jumper from 1 to 4 on this relay, correct ?

I believe you would find that the red wire in this box goes back and powers the circulator for that zone. You will find that circulator has one side connected to a white, and the other side connected to that red.

On relay #1, plywood background, I also see one cable coming in the bottom, but it looks like that cable has 2 of each color ? Are there actually TWO cables there ? Is there a DUAL BX connector on the bottom of that box ?

It appears that there are TWO conductors still wrapped in paper, not terminated, is that correct ?

I think I see 2 WHITE on term 2, 1 black on term 1, a red jumper from term 1 to term 4, 1 black on term 3, and 2 unused conductors (both red ?) is that correct ?

I think you will find that one of those cables goes to the line voltage thermostat, and the other goes to the circulator, yes ?

How is the line voltage thermostat mounted ? Is there a J-box behind it ? Did you run the new thermostat wires into that box ? If so, you can remove the two wires from the line voltage thermostat, wire nut them together (WITH THE POWER TURNED OFF!) and tuck them in the back of the box. If you do this, you won't have to rewire anything on terminals 1,2,3,4. But, ONLY if there is a proper electrical box behind the thermostat. If you are moving the thermostat, you could still do this, but you would not be allowed to cover the box inside the wall. You would have to put a blank cover on it and leave it exposed. (electrical codes). Strictly speaking, you really shouldn't have low voltage and high voltage wiring in the same box, but I really don't see a reason to NOT do it this way.
 

Last edited by NJT; 03-02-08 at 12:26 PM.
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Old 03-01-08, 08:12 PM
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I figured it out, and its working perfect! Thank you all, Trooper, thanks! I traced the old 120 wire back to the a box where it was getting power. Clipped out the wire going back to thermo, and wire nutted it in the box. Then took out the jumper between the TT and hooked that up to the thermo. So far so good!

you guys are awesome! Next task is to learn what the heck all these valves do on the boiler, and how to bleed and clean out the system.
 
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Old 03-01-08, 08:16 PM
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I just saw your other post, looks like I was writing as you were writing.

So if its working, I prob did it correctly right?
 
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Old 03-01-08, 08:36 PM
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Originally Posted by burmjohn View Post
Next task is to learn what the heck all these valves do on the boiler, and how to bleed and clean out the system.
Ask away ... more pics is fine ...

Originally Posted by burmjohn View Post
So if its working, I prob did it correctly right?
I think so! No fire, didn't have to call 911, AND it's working... cool!
 
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Old 03-01-08, 09:47 PM
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I will for sure tomorrow.

I'd really like to learn how to cut / sweat pipe. There are a few baseboards i'd like to extend and re-route.

Again, thanks for the help!
 
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