I got a good deal on a Honeywell Wi-Fi thermostat, but the downside is that it requires the C wire. Right now I just have the red and white wires going to my current thermostats. It looks like based on the attached diagram, I need to tie in to either the T or TV terminals (or both?), but I am not positive.

Right now the T and TV terminals are run over to the zone control valves and jumped between the 3 valves. How do I get that 24V ("C wire") to the new thermostat?



Thanks!

 

Based on my understanding of your description, the fact that you have zone valves, it means that you have a separate transformer powering the zone valves... is that correct?

If that is the case, the "C" wire will NOT come from the boiler controls, but rather from the transformer that powers the zone valves.

Please fully describe how your zone valves are wired, what make/model they are, and where they are getting their power from.

Is there a 'spare' wire in the thermostat cable that you can use for the "C" wire? If not, you will have to run a new cable (obviously?).

 

Yes, I believe that there is a transformer powering the zone valves. I will have to go down there and either take a picture or draw up a wiring diagram for how they are wired.

Unfortunately there isn't an extra wire in the cable running to the thermostat, so I would have to run a new wire.

 

Yes, a picture AND a diagram would be helpful, but if you tell me the make/model of the zone valves, I can surmise the wiring... that doesn't always mean they are wired correctly though!

 

I am going to try and go in the basement and take a picture tonight. The in-laws were visiting us this weekend so I didn't get around to it. I will do my best with the pictures, but my basement is a crawl space and the installer mounted the zone valves as close to the ceiling as he could (as well as the boiler itself) to reduce the amount of pipe so it is tight.

 

Ok, here are some crappy pictures. It was really hard to get them because of the way it is situated. I will try my best to explain:

This first picture shows the transformer (in the background) and the blue and yellow wires attached to the thermostat wire)


Here is a picture of the zone valve wiring (I couldn't figure out the make because of the way they are mounted):


So in the zone valve wiring I think the transformer goes to the lower left and lower right lugs (which were labeled TH/TR and then TR). Then those were jumped to the two other zones.

The wiring from the terminal block on the boiler went to the top two lugs labeled END SWITCH and were jumped to the other two zones were jumped from there.

The thermostats were wired to the two bottom left lugs (TH/TR and TH).

 

Is that transformer in the background dedicated to running ONLY the zone valves? In other words, it is NOT one of the two transformers in the boiler wiring diagram? Or is it?

If it IS one of those two transformers, why is it not connected to the boiler terminal strip as shown in the wiring diagram?

When you say "...attached to the thermostat wire..." does that wire actually go to a thermostat?

It appears to be a Honeywell V8043F.

By saying "...the terminal block on the boiler..." you mean that the ENDSWITCHES are wired in parallel and are going to the " T " and " TV " terminals on the boiler terminal block, is that correct?

The zone valve wiring appears to be correct, the only thing I'm still not clear on is where the transformer that powers the zone valves is located.

I need to be clear on this because it has everything to do with where your " C " wire is going to connect to the new thermostat.

 

That transformer pictured in the background also has a black and white white going to L1 and L2 at the boiler terminal block. And no, that thermostat wire doesn't go to the thermostats, I just called it that because it looks like it is just thermostat wire.

As far as the End Switch connection, your assumption is correct.

The only wires going to the zone valves are those yellow and blue wires and then the T and TV wires (as well as the thermostats themselves).

 

OK, but I'm still not clear... not a definite answer.

Understood that the primary of that transformer comes from the L1 and L2 120VAC supply.

But, is is one of the two transformers shown in the boiler wiring diagram?

Or is it a THIRD transformer that was added to power ONLY the zone valves?

The blue and yellow wires come directly out of that transformer, stopping NOWHERE ELSE, are connected to that red and white 'thermostat wire', then go the TH/TR and TR terminals of one of the zone valves...

 

Yes, correct, those blue and yellow wires go nowhere else. They added that third transformer specifically for the zone valves apparently. Here is a picture where you can see that they wrote in permanent marker and it says "Zone Valve 24V Power" with an arrow pointing to it (you can also see the other two transformers).

 

OK, that's the answer I was looking for!

Now that's out of the way, the actual answer is easy.

The " C " wire for your thermostat will connect to the " TR " terminal of your zone valves.

Seems like an awful lot to go through for that, doesn't it?

 

Awesome, thanks for the help! Sorry I didn't explain it very well the first time. Now I have to decide if I want to control two zones with one thermostat. The way the heating was originally done is dumb in my opinion. I have a single story ranch home that is about 1450 square feet. The boiler is set up with three zones; two zones of heat and one zone for the water heater. One zone controls the main living area of the house and the other zone controls the 3 bedrooms (with one room on one side of the house and the other rooms on the opposite end. The thermostats share the same wall and are pretty much back to back.

I only got one wifi thermostat because I didn't want to spend the money to get a second. So I am debating on just wiring it up for the main living area or if I should just wire the two together and control both zone valves with the one thermostat (assuming that is even safe).

 

Nothing really unsafe about it...

The way I would do this would be to separate the endswitch wiring on the two zone valves you want to run in tandem.

Disconnect the thermostat from the appropriate zone valve and connect the ENDSWITCH from the tandem zone valve to the THERMOSTAT connections of the second valve.

That's not very clear, is it...

New thermostat wired to one of the heating zone valves as described. Separate the endswitch wiring from THAT zone valve from the other two (the other two will remain wired together and to the boiler).

Remove thermostat wiring that you will NOT be using from the other zone valve.

Wire the endswitch from the FIRST zone valve to the same points that you removed the thermostat wiring from on the second zone valve.

What will happen is this:

On heat call from new thermostat, first zone valve will open.

When that endswitch 'makes' it will signal the second zone valve to open.

When that endswitch 'makes' it will signal the boiler to fire.