Thermostat Wiring / Boiler Inquiry

MooseOnaHill

Hello all, 

I attempted to start my Weil Mclain dual system before winter as I always do. After performing routine maintenance, my boiler wouldn’t  fire up. After troubling shooting, I discovered there’s no low voltage reading coming to the boiler which starts at the gas valve. 

I went to the thermostat and discovered there were wires disconnected which was probably from a summer renovation that took place. 

I’m getting 24 V from the transformer to the stat, but from the stat down to the boiler I have nothing. The wires are old (cloth type) but I fear I may be wiring the stat incorrectly. 

There’s two wires from the transformer and 3 low voltage wires from the stat to the boiler - One which isn’t used as I traced it downstairs. 

My Stat has RH RC W Y C B connectors. My guess is the 24V goes to the RC while the other transformer wire goes to the C ? Or is this incorrect ....?
currently the 3 wires from the stat going to the boiler are Red to RH and White to W - the yellow isn’t used. 

Thanks for your help 

Jamie Hall

What wires are connected to which terminals on the boiler control?

MooseOnaHill

This is a old system - Bear with me. 

As the wires enter the boiler, there’s a splice. The red goes to red which also connects to the Low Water Cut-Off and the Aqua Stat which ultimately connects to a single terminal on the gas valve. 

HVACNUT

Red to Rh and White to W. Just like it was. If this is a new 24 powered thermostat, then you need to connect the Common. Yellow is not typical but it's what you've got. Yellow to C on the thermostat and C on the transformer. 

MooseOnaHill

Thanks for the help man. No this is a pre existing System- But, where do The two wires from the Transformer to the stat go? Right now, I haven’t connected those because I’m unsure where they go. The 3 wires from the stat to the boiler are like you mentioned- Red to RH and White to W. The yellow isn’t connected to anything nor is it connected anywhere on the boiler. 

Zman

What model is the t-stat? It may need a common which would go from the C on the transformer to the C on the t-stat.

There is only so much troubleshooting you can do without voltage meter and some know how. One easy test is to jumper (or just touch together) the wires going to RH and W on the t-stat. If the boiler fires, you have a t-stat issue. If this boiler does not fire, try jumping the same wires in the boiler room. If it fires, you have a bad wire to the t-stat, if it does not fire, the problem lies somewhere in the boiler room and will likely require a technician.

HVACNUT

Only one wire from the transformer goes to the thermostat. R. When the thermostat (switch) closes, 24v goes through W to continue the circuit. It may not go directly there though depending on how its wired. Common doesn't go to the thermostat unless the thermostat is 24v (not battery or mercury or bi-metal) powered.
Are you saying the wires are off the transformer and you don't know where they go? If that's the case, we'll need pics and maybe the system wiring diagram. 

MooseOnaHill

Thanks fellas : 

to answer both , the model is a Lux PSP511CA- There is an unused Common port. 

I did discover that  the two wires from the transformer weren’t connected ; probably from a recent renovation. So yes, I wasn’t sure where they connected into the stat because there’s an RH and RC port.  The RH is currently occupied by one Red wire which travels down and connects at the boiler - there’s no power there. 

I’m going to preform the jumper test. But just to be clear, I’m taking the two wires from the Transformer and touching one to the RH and one to the W connection? Wiring isn’t my thing. Thanks in advance. 

Zman

Maybe you should post a couple pictures. As long as no one messed with the wiring in the boiler room, you can jump the 2 wires that are connected to the t-stat. If you can locate those same wires in the boiler room, you can jump them as well.
If the wires in the boiler room have been changed, we should probably take look so you don't let the smoke out of the transformer, they don't work if the smoke comes out.

Jamie Hall

MooseOnaHill said:

Thanks fellas : 

to answer both , the model is a Lux PSP511CA- There is an unused Common port. 

I did discover that  the two wires from the transformer weren’t connected ; probably from a recent renovation. So yes, I wasn’t sure where they connected into the stat because there’s an RH and RC port.  The RH is currently occupied by one Red wire which travels down and connects at the boiler - there’s no power there. 

I’m going to preform the jumper test. But just to be clear, I’m taking the two wires from the Transformer and touching one to the RH and one to the W connection? Wiring isn’t my thing. Thanks in advance. 

If I'm understanding what you are saying... ah, no. What you want to do is to cross RH and W and see if the boiler runs. Leave the 24 volt wire or wires from the transformer alone for the moment.

As far as the boiler control is concerned, all it needs to know is whether or not there is a connection between the two thermostat terminals on the control (a picture of the control would help a lot here). If there, is, heat is wanted and off it goes. If there isn't heat isn't wanted and it stops.

MooseOnaHill

Gotcha.... ok, I did that and got nothing. But without the 24V coming from the transformer, how would the valve know when to open? 

Here is a picture of the gas valve , gas valve up close and wiring diagram

the transformer you see attatched to the boiler is separate from the one I mentioned. This one is for a different thermostat for the H.W side

hot_rod

do you have a test meter to determine if you have 24v at the transformer?

MooseOnaHill

Yes I’m getting 24 V from the Transformer and 24 V from the two wires leading to the T-Stat. 

Jamie Hall

Check all the grounds. Also, if you have two transformers, things can get really messy. It would help -- a lot -- if you could draw a true wiring diagram of the system, showing both transformers etc. etc.

Zman

It looks to me like a millivolt system. It also looks like the boiler safeties are in series with the T-stat. I believe there is a wire missing on the gas valve. The transformer in the picture looks like it is part of a pump relay.
Please be careful in how you proceed, you could easily bypass a safety by accident and create a very dangerous condition.
Try drawing a schematic of this, it probably looks like a big daisy chain.

Zman

Does your t-stat have batteries? For this to work you will need to have the pilot lit and gas valve in on position. Don't get any of that started until you figure out what is wrong with the wiring. With an older system like this it would be very easy to accidentally end up with a runaway boiler, please be careful, if you don't have a high limit, one missed wire could result in a dangerous condition.

MooseOnaHill

Yea, you are correct. It’s part of a milli system and the pictured transformer does go to a circulating pump which controls the Hot Water feed to two radiators on the extension side of the house. 

The safeties are indeed tied to a series. I have a tech scheduled for next week so once they diagnose the issue, I will post here. Thanks for looking into it. The plumbing aspect I fully understand and can trouble shoot  but wiring is beyond my understanding. 

Stay tuned 

Zman

If this were mine, I would have them convert the t-stat wiring to 24 volt using a relay. This would give you a 24 volt common wire and a more robust connection to the t-stat.

MooseOnaHill

First, Thanks everyone for commenting and trying to rectify this issue. I just had a service Tech come in and diagnose this problem. What threw him and perhaps some of you off was that this is indeed a Mili Volt system but the thermo coupling suggested this was a Valve needing 24V ; The combination pictured threw the tech off.
To Zmans point, there was a wire disconnected at the Valve. Once he connected the White spliced wires to the other unoccupied terminal, we got power to the valve..
***How this got disconnected is beyond me***
As far as the thermostat, the wires from the transformer that i originally found disconnected, must of been to a different thermostat before i moved in. They're just to hard wire the stat... They're currently disconnected because of the current model i have in place. you guys were on the right track ,

thanks again