What are these devices in my system?

andrew000

First off: thanks everyone helping on this forum!

I've recently moved into a new home and now have in-floor heating powered by a boiler.  This is the first and only boiler I've seen in my life and motivated by "it's not working right" I'm trying to understand the system to figure out what's right and needs changing.

Google and YouTube got me to a point where I understand the theory, but when I start tracing my system I still have questions.

Starting with the flow of electricity, I'm led to expect a transformer that will take the 120v down to 24v.  But I have some other device that I don't even know how to Google (or search these forums).  Can someone tell me what this is?  Bonus for telling me why it would be used instead of the transformer, but with a name to search I can probably piece that together myself (eventually).  I do note it has Y G W C R labels, which sounds like what a thermostat might have 🤷‍♂️

My next puzzle after that is another device I don't know how to search about.  The diagram on it makes me think it's a type of switch.  But why would some of the zone valves be going through this guy on their way to the boiler while other ones don't?

bburd

As the label says, that is a relay. It's labeled to allow a 24 volt, 40 VA (watt, more or less) control circuit to switch a 120 volt, 300 VA power circuit. For instance, a 24 volt thermostat can switch a 120 volt burner or circulator pump through this relay.

There must be a 24 volt transformer somewhere.  It may be the black box on the right, I'm not familiar with that particular device.

what is wrong with your system?

HVACNUT

The first pic is a Fan Center. It's a transformer (on the left with the thermostat terminals), and a relay (on the right).

R is 24 volts out. 
On a closed switch from wherever (usually a thermostat or zone panel end switch), 24 volts will travel back to G on the Fan Center and energize the coil of the relay. (See the Black wires leading from G and C)
When the coil is energized, the Normally Open contacts on the relay will close and send 120 volts to wherever the B/X cable on the right is going.

The other pic is also a relay. Double Pole, Double Throw (DPDT).
It's only using 1 set of Normally Open contacts. 

andrew000

Thank you both for your prompt and useful replies.

Okay, so the first one IS a transformer (with bells and whistles). I opened it up to see what was going on and to map to what you've both described here.

I see the romex feeding it from behind, so all the exposed terminals should be 24 volts. Gotcha.
The circuit from R to G run to 3+ zone values in parallel (3 immediately available, and another line that I presume is running up to the 3 valves on the upper floor). Those are the red wires on the valves, so that would be the end switch circuits I'm looking at here.

The black on G and C connect to the relay sitting beside it with black+yellow on the relay's other side that are interrupting the circuit to one of the pumps. This is good. It means that pump should only be running when a valve is open. Better than what I thought was happening -- that the pump was permanently running. It's just pretty much always running because those valves are pretty much always calling. And I can feel that pump running, so I know this part of the system is functioning. Nice.

As for the power to the valves themselves, I see them connected to C and R (with thermostats upstream). That seems good.

To @bburd 's question:

bburd said:

what is wrong with your system?

When either of 2 zones call, the boiler fires. When the other 6 zones call, the boiler sits idle.

So now I see the circuit with the End Switch. When closed, it connects R to G. That will then activate 2 other circuits on G and C. The first being the relay on the same box that connects to a pump. The second is the DPDT relay in the second pic of the original post.

If I'm seeing it right, when any of the End Switches are pressed, then I'll get 24v coming from the Fan Center. Wouldn't those be usable directly to tell the boiler to light up? Instead there's a DPDT relay. The other side of it is connected up with the 2 remaining zone valves (the working zones) before feeding into the boiler. So this relay should not be transforming the voltage in any way or one side wouldn't be 24v.

Theory: it's there so that when one of the remaining 2 zone valves call, that closed circuit doesn't flow back up to the top relay and turn on the pump for unrelated zones. Did I get that right?

If my understanding is correct, then it should be safe for me to bypass and connect the outputs of the 2 working zone valves with G and C on their way to the boiler. Then if my boiler fires when only one zone upstairs calls, then my DPDT switch must be dead.

I'll attach more photos so people can see the whole system; though wires everywhere makes it hard to trace. I have no idea how/why the zone control board is wired the way it is; but since it's working for some of the zones, I figure it does function as-is. Not sure why the extra hoopla with the second pump when the board has connectors for 2 pumps already /shrug

andrew000

Photos:

Jamie Hall

A perhaps minor correction -- or maybe not. The boiler does NOT need 24 volts on anything to fire up. What it DOES need is a closed circuit between T and T on the control. In fact, depending on the source of the voltage, applying voltage to one or the other of the T terminals can have very unhappy results. This is why end switches or relays are often used on more complicated systems (such as your spaghetti bowl), while a thermostat is in essence just a switch which may be either open or closed, depending on whether heat is not wanted or wanted, as the case may be.

mattmia2

The boiler has its own transformer, the thermostat just closes a contact for it to call for heat so the second relay likely is to isolate the transformer in the boiler(these are usually the TT terminals on the boiler but they can be labeled other things, especially if the boiler manufacturer used a fan center in the boiler).

Do the 2 zones that do work connect their end switches directly to TT on the boiler?

When R-G closes on the fan center that should close the relay in the fan center.

24vac on the fan center, R and C, probably goes to the thermostats and zone valves to control the zone valves. The zone valve end switches then control the fan center relay which controls the circulator and the isolation relay for the boiler.

Is there more than one circulator in this system? My first guess without tracing anything is that the fan center controls a circualtor with a mixing valve for the radiant floor heat zones.

Try sketching this out, it will be a lot easier to follow for both you and us.

andrew000

Jamie Hall said:

A perhaps minor correction -- or maybe not.

Excellent point. And not minor at all. Okay, now that relay makes 100% sense. And you've saved me from doing a Bad Thing to test it. I'll test that relay a different way. After work.

andrew000

Update. Did a quick test.
Relay has continuity on the coil side (expected). Disconnected the leads to the boiler and tested continuity with zone valves open. Nada. I guess I need a new relay?

So I understand I need one that triggers on 24v. Not sure what other parameters I need to check to ensure it's up to the job. The existing relay has ratings with 125V and 250V. But I guess that's because it doesn't really care what voltage is on the switch side?

Current relay:
W-R/RBM
91-132006-13083
90-340
CONTACT RATING
12 AFL 60 ALR 125V
6 AFL 35 ALR 250V
60HZ

Do I need to find the specs of my boiler to know what current it would be sending through the circuit for the end switches? Or would something like this guy https://www.amazon.ca/TWTADE-Electromagnetic-Indicator-（Quality-Assurance/dp/B07DHGXMLW/ref=sr_1_1?crid=ZMDRQV7AAP9D&keywords=24v+relay+din+rail&qid=1701474732&sprefix=24v+relay+din+rail,aps,124&sr=8-1&th=1 be good enough and call it a day?

andrew000

Follow-up to this:

I found the circuit diagram for my boiler and it showed a 2.5A fuse for that circuit. So I grabbed a relay and swapped it in. Magic! Looks like one zone valve isn't sending the signal (so either zone valve itself not hitting the end switch, or the wiring). But that's down from 6 zones not firing the boiler down to 1 zone not firing the boiler. Excellent improvement!

Thanks again to everyone here who helped me navigate my way through.

mattmia2

was the relay bad or were you testing with the zone valve with the bad end switch?

andrew000

The relay was bad, which stopped 6 valves from triggering the boiler. (the remaining 2 valves were connected directly to the boiler).

Once the relay was fixed it was possible for the valves to trigger the boiler. And 5 of them do. It seems one zone had 2 faults. So additional work will be needed to get that one going.