Rewiring an emergency bypass fix + new C Wire connection.

wayngrove

Hello again my HVAC heroes! Time again for another DIY life raft to be thrown my way.

I recently had my zone 2 thermostat burn out on me, but in my ignorance I thought it was the Taco 555 power head (the old green one was very hot to the touch) to my oil boiler. I ordered and installed the new power head but the zone never opened when heat was "called" from the (still unknown to me) burnt out thermostat. I then discovered the burning smell was coming from the thermostat, so I immediately thought I may have rewired the heads improperly and I called in the pro who installed the unit. He said not only is the thermostat burnt out, but BOTH of my power heads were as well. In order for us to have heat, he bypassed the power heads altogether by wiring the Zone 1 thermostat directly to the boiler control panel and set the Taco valves to manual open. I now do not recognize the wiring configuration to properly install the new power heads.

On top of this, I ordered 2 Emerson Sensi Classic Wi-fi thermostats, not knowing a C Wire was needed. I have the basic 2 wire setup, so I fished a 3rd wire through the walls for both zones, but I don't know where to connect on the boiler end.

I need to know 3 things:

1. Where to connect the R and W wires that originate on the wall Transformer and run to the Taco valves
   
2. Where to connect the R and W wires that originate on the Boiler Control Panel and run to the Taco valves
   
3. Where to connect the 2 new C Wire feeds for the thermostats.
   

Thanks in advance.

Steamhead

Those two transformers are probably wired together in parallel. I HATE that hookup- it's way too easy to burn something out.

The basic problem is that with this type of ZV, the incoming 24V power from terminal R on the transformer is connected to terminal 2. The thermostat is connected between terminal 1 and terminal C on the transformer. This means that when the ZV is activated, there is no 24V power to the thermostat, so the electronics go dead.

You'll probably end up powering the thermostats directly and having them operate isolation relays which then actuate the ZVs. Also, you'll want to have terminal 3 of each ZV connect to another isolation relay, whose contacts will connect to the thermostat terminals on the aquastat relay. This will separate the two transformers and drastically reduce the chance of a burnout.

Any convenient relay with a 24V coil will work for your isolation relays. The Honeywell R8222 series is a good choice, since you can screw it directly to the backboard near the wall transformer.

STEVEusaPA

Move those 2 blue wire nuts (especially the 1) away from the relay.

wayngrove

> @STEVEusaPA said:
> Move those 2 blue wire nuts (especially the 1) away from the relay.

Okay will do as soon as I get home. Are you asking for a better view, or is it unsafe as-is?

Steamhead

@wayngrove , where are you located?

wayngrove

> @Steamhead said:
> @wayngrove , where are you located?

Philly Burbs

STEVEusaPA

wayngrove said:

> @STEVEusaPA said:

> Move those 2 blue wire nuts (especially the 1) away from the relay.



Okay will do as soon as I get home. Are you asking for a better view, or is it unsafe as-is?

I'm just saying don't let the wire nut affect the operation of the relay.

mattmia2

Putting the transformers in parallel makes them no longer class 2. The NEC doesn't allow you to do it.

STEVEusaPA

Or just get a zone panel. Newer Taco's are set up for 3 wire.

mattmia2

These are a nice way to do it too, they have leads and you can mount them all to a 4" box and hide the rat's nest behind a cover:
https://www.supplyhouse.com/Functional-Devices-RIBU1C-Enclosed-Pilot-Relay-10-Amp-SPDT-w-10-30-Vac-DC-120-Vac-Coil

HomerJSmith

News Flash, guys. Transformers are wired up in only 2 ways, parallel or series. I always wire up 2 trans in parallel. The only thing to remember is that the phasing of the 2 trans secondaries are correct. The big mistake is wiring up 2 trans out of phase. That can lead to excessive heat and eventual failure.

If there is a direct short of a class 2 trans secondary, it would blow the fuse wire in the primary and render the trans inoperative.

Homer's easy way to tell if 2 trans secondaries are in phase. Wire one secondary from each trans together, then scratch the other secondary wire from one trans across the secondary of the other trans, quickly, then observe the spark. Then switch the secondary of one trans and wire it together and quickly do your scratch again. The connection with the lowest spark is in phase.

Or...

HomerJSmith

When these aquastats were set up the trans in the box operated the circulator relay. The TT connections were only a switched connection by the mercury thermostats. The only loss in the circuit was resistance which was nil.

Along came digital thermos, power robbing thermos, and Wi-fi thermostats as well as zone valves. The power demand by these devices increased. So, it may be necessary to add another power source to the existing transformer. That's where trans phasing is important if they have common connections.

HomerJSmith

wansgrove--What kind of thermostat was it that got blowd up? This inquiring mind wants to know. Anytime something's burning, it's drawing too much current for the rated device.

I would really want to understand how a thermostat burned up.

Think of your situation as two different operations. The boiler circuit and the thermostat Wi-fi charging circuit and ZV heat motor.

The boiler circuit--the aquastat transformer sends 24V out of one of the TT connections, up a wire to the #2 connection on the Zone Valve, the #3 connection of the ZV goes back to the other T connection on the aquastat. That's the circuit that turns on the boiler (it just a switch).

You need another auxiliary transformer to allow the thermostat(s) to turn on the heat motor(s) in the ZV(s).

The power output of the aux transformer must be greater than the power requirement of all the Wi-fi thermostats and ZVs connected to the auxiliary transformer. One secondary connection of the aux trans (let's say the R wire) connects to the R connection in the thermostat (the 24V power wire), the W connection on the thermostat send the 24V down the wire to the #1 connection of the zone valve, which is the heat motor of the ZV, the 24V goes thru the resistance winding, actuating the heat motor, exits out the #2 connection on the ZV, back to the aux transformer secondary connection (let's say the W wire), creating a circuit, switched by the thermosat.

This is important for Wi-fi thermostats! The C connection on the thermostat must connect to the secondary connection on the aux trans W connection. WahLa, all done.

I like the aquastat transformer and the aux transformer to be in phase.

EBEBRATT-Ed

@Steamhead 's approach with using Isolating relays is the best fix.

mattmia2

I was just thinking of @HomerJSmith 's last solution. It solves the problem and doesn't violate the nec.

wayngrove

> @HomerJSmith said:
> wansgrove--What kind of thermostat was it that got blowd up? This inquiring mind wants to know. Anytime something's burning, it's drawing too much current for the rated device.
>
> I would really want to understand how a thermostat burned up.
>

Here's the photos of the dead TS. Just got in from work so I have some reading to do here.

HomerJSmith

That was caused by at least 110V. You wired up something wrong and I suspect crossed it with 110V. If you wired up a transformer and it has primary (110V) leads and secondary (24V) leads, did you hook up the 110V power in to the secondary leads? That would do it. The black and white leads go to the 110V power in leads. Is the transformer a 110V in and 24V out and not 220V in?

A 24V thermostat wouldn't burn like that even if shorted, the fuse wire in the transformer would blow.

HomerJSmith

Look, it's ok to have a white coiled jumper wire between ZVs on the #2 & #3 screws. It doesn't have to be 10' long. Those #2-#3 screws must be connected to the TT connections in the aquastat, so when the end switch in the ZVs close it turns on the boiler. If that red wire that is disconnected in your picture which has the white wire connected to the #2 screw on the left ZV and it goes to the TT connections on the aquastat, then connect the loose red wire out of that cable to the #3 screw. That solves 1/2 of my wiring diagram.

If you have a volt meter ( you can buy one from Harbor Freight for peanuts), measure the continuity between screw #1 & #2. Don't have any other wire connected to the #1 screw. If it shows continuity, the ZV is probably ok. Put the meter on the Ohm setting and do the same. The Ohm reading should be somewhere greater than 5 Ohms, but not 30 Mega Ohms. Perhaps 50 Ohms. If so, that would probably be an ok power head.

Now you need to work on the Wi-fi thermostat, aux transformer ( wall transformer?), and the ZV. Follow my diagram as to hookup and how the C wire connect to the aux trans. Each ZV should have it's own thermostat. The C wire from the thermostats connects to the transformer and not the ZVs.

mattmia2

You could burn something up like that with 24v if it was through a bad connection rather than a short. A short would blow the fuse in the xfmr. Highish resistance could generate enough heat to burn up stuff. Paralleling the xfms means there is more power available that could generate more heat in a fault, that is why the code doesn't allow it (although from an engineering standpoint it is ok as long as the total is under 90 va).

That said, it is very likely something touched in that sloppy wiring in the aquastat-relay.

wayngrove

HomerJSmith said:

That was caused by at least 110V. You wired up something wrong and I suspect crossed it with 110V. If you wired up a transformer and it has primary (110V) leads and secondary (24V) leads, did you hook up the 110V power in to the secondary leads? That would do it. The black and white leads go to the 110V power in leads. Is the transformer a 110V in and 24V out and not 220V in?

A 24V thermostat wouldn't burn like that even if shorted, the fuse wire in the transformer would blow.

The only thing I could have done is wire the ZV incorrectly when swapping it out. The pro did say I was lucky that both the aquastat and transformer didn't blow.

HomerJSmith said:

This is important for Wi-fi thermostats! The C connection on the thermostat must connect to the secondary connection on the aux trans W connection. WahLa, all done.

I like the aquastat transformer and the aux transformer to be in phase.

Your diagram, when I manipulate the physical wires, is exactly the way I remember it prior to the issues. I'm going to wire it and post some more pics prior to throwing the power on. For the C wire, Since it's connected to the Aux Trans W, and the #2 ZV post is as well, is it okay to secure it there, or should I run the wire to the Aux W post? The Aux W post doesn't have a lot of room on it

wayngrove

HomerJSmith said:

The C wire from the thermostats connects to the transformer and not the ZVs.

You already answered this here. Sorry I missed it. Now I have to reread everything to make sure I didn't miss anything else

wayngrove

HomerJSmith said:

Look, it's ok to have a white coiled jumper wire between ZVs on the #2 & #3 screws. It doesn't have to be 10' long. Those #2-#3 screws must be connected to the TT connections in the aquastat, so when the end switch in the ZVs close it turns on the boiler. If that red wire that is disconnected in your picture which has the white wire connected to the #2 screw on the left ZV and it goes to the TT connections on the aquastat, then connect the loose red wire out of that cable to the #3 screw. That solves 1/2 of my wiring diagram.

Now you need to work on the Wi-fi thermostat, aux transformer ( wall transformer?), and the ZV. Follow my diagram as to hookup and how the C wire connect to the aux trans. Each ZV should have it's own thermostat. The C wire from the thermostats connects to the transformer and not the ZVs.

How does this look?

HomerJSmith

Taco Wiring Note:

"While two circuits, each with its own transformer, touch at terminal #2, they do not communicate or interfere with each other in any way ... Each circuit flows only in that circuit. This occurs because the transformer in either circuit cannot cause a voltage or current driving force to be realized in the other circuit when joined only at one point to that circuit."

I'm not sure how your first picture wiring with the blue wire nut and the Tstat 1 and Tstat 2 wires are hook up to the aux transformer and the thermostats.

The coiled jumper between the two ZVs appears correct.

I would want to put a volt meter on the thermostat to check voltages before I felt safe. Unplug the thermostats from the base so that you only have the R W C contacts exposed and unconnected to the thermostats circuitry. Open the manual lever on the ZVs. Jumper the #2 and #3 screws on the ZV for that thermostat and measure the voltage between R & W and R & C for that thermostat. It should be 24V. Measure the voltage between W & C. It should be 0V. Repeat with the other ZV and thermostat base.

I would want to know why that thermostat burned up.

wayngrove

> @HomerJSmith said:
> I would want to know why that thermostat burned up.

I never did anything with the transformer wiring. This boiler was installed in 2011 and has been functioning normally since then. What I think I did was wire the coiled jumper incorrectly, maybe sending two hot wires to each end of the thermostat. Could that have caused the burnout?

HomerJSmith

Two transformers wired up in series would certainly double the voltage from 24V to 48V.

wayngrove

I picked up a voltmeter on my break and I'll start testing tonight

wayngrove

> @HomerJSmith said:
> I'm not sure how your first picture wiring with the blue wire nut and the Tstat 1 and Tstat 2 wires are hook up to the aux transformer and the thermostats.

• TStat W for both are on their respective ZV's 1
• TStat R for both are connected in wire nut with Aux Trans R
• Aux Trans R is between the 2 TStat Rs and the Aux Trans C terminal
•Aux Trans W between the Left ZV's #2 and the Aux Trans R terminal

> @HomerJSmith said:
> Jumper the #2 and #3 screws on the ZV for that thermostat and measure the voltage between R & W and R & C for that thermostat. It should be 24V. Measure the voltage between W & C. It should be 0V. Repeat with the other ZV and thermostat base.

Got 24, 24 and 0 on both TStat bases

wayngrove

Just a follow up; all is well. @HomerJSmith suggestion and wiring was spot on. Thanks to everyone who pitched in on helping out.