What is the AC Motor doing in this boiler configuration?

4lane

I have a new home with an old Weil McLain gas boiler. I am looking to run a 3-wire to it so I can put in a new thermostat but I see a transformer and an A/C motor in the wiring flow which is one more element than expected. The wiring is a bit confusing as a result. What is the transformer and AC motor doing exactly?

EBEBRATT-Ed

I can't see an AC motor in the pictures. That looks like a limit control. Is this a boiler (heats water) or a furnace (heats air)? Weil Mclain used to mke both

In any event. the common wire you need can be connected to the transformer in the picture

JakeCK

I'm curious who or what told you that was an AC motor?

And the transformer is transforming 120vac to 24v for use by the t-stat, gas valve, and any other low voltage devices such as auto dampers. It is also used for proving all the safeties are good. 

4lane

I actually don't know what that thing is for, but it says AC Motor on it, so that's what I'm referring to it as. Here is the current wiring flow, if that helps.

JakeCK

It say ac motor on it? I cant read the the writing because the photo is to low of a resolution. Is that a wiring diagram you made or found?

Now if that WM boiler is like mine, that is the aquastat and controls the opening and closing of the gas valve based on water temperature. It is a high limit safety to keep your boiler from over heating. No motor involved as far as I know. The only motors you should have on that old of a boiler is perhaps a circulator, which would be 120v, and a vent damper if equiped, which would be 24v.

mattmia2

It isn't an ac motor, that is a rating of the contacts for an AC motor load being switched by that limit thermostat if it were connected to an ac motor instead of in the low voltage circuit.

4lane

It does also say Limit Control on it. Here's a close up. I made the wiring diagram so I could document the current set up. With the new 3 wire, I'm planning to keep the exact same wiring, with the addition of the 3rd wire to the C terminal, like this:

Jamie Hall

Are you quite certain of the existing wiring? I'm not...

ChrisJ

That's an aquastat no?

4lane

Yes, I am certain of the existing wiring.

STEVEusaPA

ChrisJ said:

That's an aquastat no?

Looks like a high limit aquastat to me. You can see the bulb going into the well.
Boiler probably just bounces off high limit all day.
Is this a gravity job, no circulator?
I also thought you aren't allowed to use a street ell on gas piping, @EBEBRATT-Ed ?

ChrisJ

STEVEusaPA said:

That's an aquastat no?

Looks like a high limit aquastat to me. You can see the bulb going into the well. Boiler probably just bounces off high limit all day. Is this a gravity job, no circulator? I also thought you aren't allowed to use a street ell on gas piping, @EBEBRATT-Ed ?

Depends on who you ask honestly.

I have one on my line outside right at the meter.  Some guys say you can't use plugs but others do.

The only consistent thing I think I've heard it's no bushings.

HVACNUT

4lane said:

It does also say Limit Control on it. Here's a close up. I made the wiring diagram so I could document the current set up. With the new 3 wire, I'm planning to keep the exact same wiring, with the addition of the 3rd wire to the C terminal, like this:

Yes, that will work. 
It should be a 40 va transformer there so it should be fine, but check its rating.
Your diagram is right but the colors of the wires are wrong. 
R- Red/ 24 volts. The one with the black wire nut at the transformer. 
And your diagram shows you connected to Rc at the thermostat. What thermostat are you installing? Typically Rc is power for cooling. R or Rh is for heating. Double check what the thermostat instructions ask for.
W- White wire to the wire that has the orange wire nut at the transformer. 
C- Common to C on the transformer. 

P.S. when I asked what thermostat you were installing, if it's a Nest, don't tell me. Thank you.

mattmia2

ChrisJ said:

The only consistent thing I think I've heard it's no bushings.

And I think technically that is only a bushing between 2 adjacent pipe sizes because the material is very thin. If it is a couple nominal sizes difference the problem goes away.

ratio

The schematic looks good to me. I've seen that style of transformer before, the W, Y, and G terminals are just splice points, only the R and C are connected to the xfrmr. @4lane, your added C wire looks good too, although I might pull in an 8 conductor wire just to have everything you'll need if you ever upgrade.

4lane

Thanks all, I have an Ecobee thermostat I'm putting in. Here's how the new wiring will look per your suggestions:

EBEBRATT-Ed

@STEVEusaPA & @ChrisJ

As far as I know street ells can be used but i hardly ever use them....just don't like them. But i have seen them used on gas valves when in a tight spot.

As far as plugs you can use them even though the larger ones (Usually over 1" or so plugs are CI )are CI the smaller ones are usually steel.

CI bushings are a no no.

The old MA gas code no longer in use used to say something about "no bull head plugs" or something like that .....no one ever knew what they meant but some took that to mean no plugs....not true. But then MA follows NFPA 54 (natural) and 58 (propane) with some amendments (like no galvanized pipe) which other locations seem to approve and in fact recommend

mattmia2

Last I looked the michigan code allowed galvanized if the sulfur content of the gas was below some threshold. so then what if the source of the gas changes?

retiredguy

The company I worked for was domiciled in a suburb of Pittsburgh, Pa. and we did both new and old commercial/industrial boiler work all over Pennsylvania with most of our work being west of Harrisburg. As far as the use of bushings, street elbows, and couplings on gas lines, we were not allowed to use them. However, the gas companies all used them on the lines before the gas meter. I frequently asked "how come you can use them and we can't". Their answer was always that they are the gas company and they could do what they wanted. And believe me, they used all of them. And @4lane, that AC motor part you are referencing, is an aquastat.

ChrisJ

retiredguy said:

The company I worked for was domiciled in a suburb of Pittsburgh, Pa. and we did both new and old commercial/industrial boiler work all over Pennsylvania with most of our work being west of Harrisburg. As far as the use of bushings, street elbows, and couplings on gas lines, we were not allowed to use them. However, the gas companies all used them on the lines before the gas meter. I frequently asked "how come you can use them and we can't". Their answer was always that they are the gas company and they could do what they wanted. And believe me, they used all of them. And @4lane, that AC motor part you are referencing, is an aquastat.

I've watched propane companies do the same thing. They do whatever they want.

dave1234

EBEBRATT-Ed said:

 Weil Mclain used to mke both In any event. 

I was surprised to learn they still do (forced air) recently 

EdTheHeaterMan

Does your boiler front door have this diagram on it? (or something like it?)



This will help in determining the actual wiring that is supposed to be there.

If your diagram is accurate then your proposed diagram will work just fine.

4lane

4lane said:

Thanks all, I have an Ecobee thermostat I'm putting in. Here's how the new wiring will look per your suggestions:

Wired this up today and I’m up and running. Thanks all!