line voltage thermostat

docbar99 · February 16

After recently installed oil burner system (hot water / baseboard) seemed to be using more oil than my 40 year old boiler, I was surprised. My thermostat was not changed and since there are so many new cool thermostats on the market I bought one. When I removed the old thermostat I was surprised to find that it was wired up to line voltage and not the 24V that most thermostats are designed for. I took a look inside my Hydrostat 3250+ aquastat I noticed that the two thermostat inputs were jumpered. I tried to trace all the wiring and came to the conclusion that the thermostat is only turning the circulator motor on and off. It seems to me that all the smarts and effecincies in the aquastat are bypassed.
My question- is this a common practice?
Would it be worth it to install a 24v transformer so that the thermostat wires can be connected to the thermostat inputs? As a newbie in oil burners, I am looking for some advice.

EdTheHeaterMan · February 16

NO. not a common practice line voltage thermostat for oil heat.
NO. Don't use a transformer. Disconnect that wire from the 120 VAC Circuit. Either run an new 18-4 wire or connect some 18 gauge wire to the 14 gauge wire and shove it behind the wall and mount a 24 VAC thermostat on the wall.

At the boiler room end, connect the 14 gauge wire to the T T terminals of the Hydrostat. If the wire does not reach then connect 18 gauge to the boiler room end of the 14 gauge thermostat wire.
Fun Fact: 14 Gauge wire can handle a 24 VAC current safely. The other way around... not so much

But running a 18-4 thermostat wire from the thermostat location to the boiler room is the better way to do it.

Connect the circulator pump to the C1 and C2 of the Hydrostat directly. That will reduce you cost of operation instantly.

docbar99 · February 16

Hi Ed- Thanks for the quick reply- You mentioned not to use a transformer, does that mean that the T T terminals can supply the 24V for the the thermostat? I was hoping that I could re-use the 14 gage wire that is connected now, after I disconnect it from the line voltage. It will not be too easy to add new wires without disturbing sheet rocked walls & ceilings. Since I only have heat only, I think I only need 2 wires.
Let me know if any of that makes sense, and thanks again

Jamie Hall · February 16

The T-T terminals do not "supply voltage" though one of them may have voltage on it. What they are looking for is either an open circuit (no call for heat) or a closed circuit (call for heat). The thermostat is just a switch, unless it is one of the fancy digital ones. Those require either batteries or a common power return wire, which gets a little more interesting in terms of wiring.

EdTheHeaterMan · February 16

You can use the 14 gauge line voltage wire from the thermostat location to the boiler location. I find that when i need to do that it is easy to connect to the thermostat with a short piece (10" to 12") of 18 gauge wire connected with a small wire nut to tyhe 14 gauge wire. then secure it with electrical tape, then push it inside the wall so only the 18 gauge wires stick thru the wall.

On the boiler end you can connect the other end of the 14 gauge wire directly to the Hydrostat screw terminals of the wire is long enough. If it is not long enough, then add 18 gauge wire in the same way as the thermostat end. Just ber sure the connection is secure.

The Hydrostat has a built in transformer so all you need or do is connect the R from the thermostat to the T on the Hydrostat and the W from the thermostat to the TV of the Hydrostat. just like in the instruction manual.

The gauge of the wire does not change the connections process. (in other words 14 gauge wire does not automatically change the 24 volt electricity to 120 volt electricity.) I needed to say that just in case anybody thought that could happen...

EBEBRATT-Ed · February 16

What your old boiler had was called a non integrated control system where the boiler maintained temperature and the thermostat controlled only the pump directly. When the new boiler was installed the installer should have made some changes

docbar99 · February 16

Thank you both Ed and Jamie for your help. Last night I opened up the Red on/off box and it looked confusing at first because there were allot of wires in there. Coming in was 2 pairs of Romex which I assumed were the AC line power from the red switch at the top of the stairs and the other had to be from the thermostat. There were 2 wires going t the circulator motor. There were 3 wires (Black, white , green) leaving the box to the Hydrostat. In the hydrostat the green was jumped to black which was a little confusing at first because in the switch box, green was jumped to white. Once I power the system down I will untangle the wires and see where they go more definitively.

Big Ed_4 · February 16

Line voltage was used on hydronic systems from 1960 -1980's , what I believe Long Island could have been one of the few areas that used them . T451 and if I remember correctly T44 ? You have to make sure the two line voltage wires are isolated to be used . Some electricians picked up the thermostat from the emergency switched .

I would recommend to run a new 18 for internet thermostats , And the old hallway location was never a good spot .

PRR · February 16

In both pictures, I see a Green wire twisted to a White or a Black wire. If this is 120VAC work, that's gross violation and potentially shocking. If this is indeed 24V work using available "120V" (300V rated)/colored wires, that's kosher, but begging for misunderstanding. Especially if a frazzled tech works in the cold dark.

Every time I do a thermostat it wants more wires (usta be 2 was plenty). My HomeDepot has in stock 50 ft. 18/5 Brown Solid Copper CL2R Thermostat Wire $24, and 18/2 (one pair) for less. These will get you through the winter. The 5 wire stuff can feed power to a "smart" t'stat (they should smartly mux onto fewer wires but they are not that smart).

If you do or know network wiring: HIGH-grade ethernet stranded cable is plenty good, and 20' scraps are nearly free. You will have to invent And Document a color code.

pecmsg · February 16

Big Ed_4 said:

Line voltage was used on hydronic systems from 1960 -1980's , what I believe Long Island could have been one of the few areas that used them . T451 and if I remember correctly T44 ? You have to make sure the two line voltage wires are isolated to be used . Some electricians picked up the thermostat from the emergency switched . I would recommend to run a new 18 for internet thermostats , And the old hallway location was never a good spot .

Just be safe
Rewire for 24 volt control circuit

EdTheHeaterMan · February 17

Can you tell us what model number your new boiler is and who makes it? Also, what is the model of the thermostat? The Hydrostat is available from many boiler manufacturers. In order to make this as simple as possible, it would be easier to put your new boiler back to the original configuration.

Then it is important to isolate the thermostat wire from the line voltage. Even remove it from the electrical box so it never gets confused with a 120 volt wire in the future, and possibly ruin your 24 volt thermostat.

With your photograph of the wires "as built" and the wiring diagram from your boiler manual, you can get to a place where it will be easy to connect a 24 volt thermostat. If you are lucky, the 120 thermostat wire has a black and a white and a ground wire. That will be the three conductors you will use for the new smart thermostat If that is what you need.

docbar99 · February 17

First - I want to thank all you guys that have responded to my post. Its amazing, you oil burner guys must have a great pride in your craft and support for each other, kind of like a brotherhood. I feel confident in doing this job myself now after reading your posts. Ok, so you guys were right, the house is on Long Island and built in 1970. The original thermostat was installed free about 10 years by Petro oil company as part of a service contract. It is actually is a Lux ELV1 Programmable Line Voltage Thermostat. (probably installed so it would consume more oil) . The Boiler is a peerless WBV-3 with Reillio burner and the the control is the Hydrostat 3250-Plus. (Three section, one zone) I am thinking, first I will isolate the 14 gage thermostat wires from the AC circuit, splice in some Ethernet Cat5 wire on the ends and connect them to the TT terminals of the Hydrostat.
Same on the new low voltage thermostat.
Then find the two wires for the circulator motor and connect them to the C1 and C2 terminals. If that works out, later I will drill/snake in some new thermostat wires as there are finised wall and ceilings involved.
Hopefully this all makes sense.

EdTheHeaterMan · February 17

What is the brand & model (number) of the 24 VAC thermostat? Actually all I need to know about the thermostat is ... Does it need a C wire connection?. If it is a Google N??T, please DON'T mention it here because @pecmsg will need to say some comment about how troublesome they are and we don't need that conversation again. (LOL inside Joke)

Only reason I ask is that the Hydostat 3250 does not have a C terminal that you can connect that thermostat C wire to. I just purchased a Hydrostat 3250 Plus so I can take it apart to see if the C spade connector for the WWSD and Outdoor reset connections is connected to the C of the transformer. I will have the update on that next week after the part arrives.

EdTheHeaterMan · February 17

It appears that Peerless offered that boiler with a Riello burner, but the only information I could find on line was that the Riello was connected to a L7224 aquastat, and there are no wiring diagrams available for that combination. The original installer may have purchased the "Boiler Less Burner" and the Peerless 91076 Riello Burner kit. There is no wiring diagram available online for that combination.

This is the best I could come up with for what your wiring diagram might look like
https://us.v-cdn.net/5021738/uploads/editor/v0/kup93eukxnoc.png

Big Ed_4 · February 18

If you have one zone you run the new 18 to TT and yes hook up the circulator to C1 hot and C2 neutral . Then make the old line voltage safe .

Tip ... That Lux runs on batteries to switch the relay . When the batteries are too low to work the thermostat , don't let the led screen fool you ....

HVACNUT · February 18

The WBV with an OEM spec'd Riello F5 and the Hydrostat 3250 Plus has been offered since forever.
@docbar99, the romex going to the thermostat goes directly to the thermostat? I've seen some that go from the circuit breaker, to the emergency switch, to the thermostat, then to the boiler with a 14/3 romex. Make sure yours is a homerun.
Some 2 story, 2 zone Long Island homes got a 14/3 (Black,White,Red) from the boiler to the first floor thermostat. White was Common. Red was the first floor Load. A 14/2 from the first floor thermostat to the second floor thermostat. White Common. Black second floor load. Who needs relays?

docbar99 · February 19

Again- thanks for all the replies. I am not a boiler guy, but do have an electronics backgraund. To answer some of the questions. The thermostat I will be installing is the low voltage type with battery backup, non- programmable, so I believe that I don't need the "C" wire. I agree that the Lux thermostat when battery low is switching is flaky, one time I went on a trip with the setpoint on hold @ 62 degrees and game home and it was 86 degrees with a near empty oil tank.
On Monday I am off and will power down the circuit and make sure that the 2 wires I believe are thermostatare directly to the boiler on/off box and not routed through the red switch at the top of the stairs.

docbar99 · February 20

Hi Guys- Thanks to your help I was able to re-wire from my line voltage thermostat that was very flaky lately to a new lo-voltage non-programmable thermostat. Seems to be working nicely.

Original wiring:

Since I don't have a C wire I did not get a programmable thermostat, because you loose all the settings when you change batteries.

I think in the summer I may rewire with new thermostat wire and a C wire adapter so I can get a WiFi thermostat. If anyone knows an easy adapter that can be installed at the burner side that is not too expensive, let me know.

HVACNUT · February 20

Good job.
The only thing I would recommend is get Blue or Red electrical tape and wrap the Green wire with it. With Line Voltage wiring, Green is ALWAYS Ground. And the one on yours is not.

docbar99 · February 20

Thanks- Will do.

Big Ed_4 · February 20

Pull the 24V wires out of the 110V box ....

docbar99 · February 21

Hi Ed- Based on your comment I guess you can't mix hi voltage and lo voltage in the same enclosure. That actually is what I did first, but it looked sloppy, so I made the connections inside. I will be replacing the thermostat wire direct from the thermostat to the hydrostat in the spring. Thanks for your input.

EdTheHeaterMan · February 21

You can have 24 Volt wires in the same enclosure as the 120 Volt wires, it is just that the 24 volt wires must be the same gauge and insulation as the 120 Volt wires. You can't put 18 or 20 gauge thermostat wire in the same enclosure as the 120 volt wires. The insulation on those smaller thermostat wires will not have the same insulation to withstand a little heat that the other wires have.

So @Big Ed_4 has good advise since we do not know if you are attaching the thinner wires to the thicker wires inside the enclosure. It is best to have all the 24 VAC wires outside the box.

docbar99 · February 21

Thank you both for your help in this process. I will be replacing the 14 gage wire with normal thermostat wire eventually so it will not need to go into the ON//OFF box, but directly to the Hydrostat. For today, can I join the 14 gage with the 18 gage wire in a separate J-Box?

delcrossv · February 21

Black to Green is making my head explode. Sorry.

docbar99 · February 21

Thanks for that comment, another person said that I could put some red tape on both ends. The original wiring had green to white one one end and black on the other. That was confusing to me as well until I buzzed it out.

docbar99 · March 18

@delcrossv- Thanks for your previous advice- I hope the changes I made will be OK. I marked the green wire with Red tape on both ends and took the low voltage wires outside of the box. Hopefuly you head will hurt a little less.......LOL

pecmsg · March 18

Using a green conductor for anything but ground is wrong and dangerous!

ratio · March 18

Depending on wire colors is wrong and dangerous too!

Electricity don't know no color. Trust, but verify.

pecmsg · March 18

ratio said:

Depending on wire colors is wrong and dangerous too!
Electricity don't know no color. Trust, but verify.

I agree, but suppose there’s a spice box somewhere else, someone sees a green wire and hooks it to the ground

wrong is wrong

EdTheHeaterMan · March 18

pecmsg said:
Using a green conductor for anything but ground is wrong and dangerous!

What about the G from the thermostat to the furnace or air handler? I always used the green wire for that. I guess I could use Gray but not too many rolls of thermostat wire have Gray?!? I used the Yellow wire for the compressor contactor and the Red wire from the R on the furnace or air handler to the R on the thermostat. When ever I can I like to use Blue for the common. But not all rolls of thermostat wire have Blue. So I end up using what ever is left over like Black, or Brown. or even Green sometimes if there is no fan relay. But I also like to install the NEST thermostat

pecmsg · March 18

That’s low-voltage

ratio · March 18

pecmsg said:

ratio said:

Depending on wire colors is wrong and dangerous too!
Electricity don't know no color. Trust, but verify.

I agree, but suppose there’s a spice box somewhere else, someone sees a green wire and hooks it to the ground

wrong is wrong

Not arguing that the grounding conductor should be used as a current carrying conductor, but you can't trust wire colors. They're just a convenience. IMHO, all wires should be black (or white, or whatever). That way, you'd have to know exactly what that wire does before you cut into it. (Only mostly joking.)

docbar99 · March 19

It's pretty clear from all of you guys that at least in hi voltage, green can only be ground. In my experience I have never seen a green wire for an AC circuit unless it is a chassis ground and that usually has a yellow stripe on it. Since that was installed by my heating contractor, it was not my idea, but I did what another forumn member said to do... cover both ends with red or black tape and that is what I did. Hopefully that is an acceptable solution. If not I can get some 14 gage red wire and replace it.

EdTheHeaterMan · March 22

pecmsg said:
That’s low-voltage

I have found 14 gauge green wires used for low voltage control circuits. And the voltage will work in any color wire and on any gauge wire. Back in 1976 I went to oil burner classes and the instructor used 18 gauge wires to make basic oil burner circuits where a 120VAC light bulb was used to indicate the motor was operating, and another light bulb was used to indicate the ignition was operating, and finally a third light bulb was used to indicate that the circulator was operating.

Now let me see. If the green wire is 14 gauge or thicker then it IS a ground, and if the green wire is 18 gauge or thinner it is low voltage, so it is ok to use for current? Except when it isn't

Of course the instructor let us know that the 18 gauge wires we were using for 120 VAC on the test boards would not be up to code for actual use. It was just easier to use for the test boards for understanding the connection diagrams.

line voltage thermostat

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