How to safely replace a thermostat connected to Taco ZVC406

jimmypenance

Hi all! First post. The heat is running constantly in our apartment making it too warm, I'm pretty sure that it's a thermostat issue because:

1. The thermostat is a really old dial dial thermostat and it's probably at end of life
   
2. I'm used to hearing a clicking when I turn the dial, that never happens anymore
   
3. Everyone else's in our 6 unit building's heat seems to be fine
   

I am not at all handy, but I'd like to attempt the replacement myself since it seems like it might be doable. But I definitely need some expert help! What I know:

• It's a simple 2 wires connecting from the wall
  
• We have a Taco ZVC406 controller hooked up to the different apartments
  
• Our boiler is BURNHAM - Boiler Model P-209, Pressure Type Low Pressure
  
• 
  

The main thing I am worried about - how to stop power to the thermostat wires, since I've just read that if I don't I could damage our control boards etc., which sounds like a great way to make my neighbors really annoyed at me. (We are self managed, there's no property management company)

So to kill the power to my thermostat - Is turning off the Taco unit enough? Do I need to turn off the boiler too?

Anything else that I should be aware of that I'm not thinking about?

Thank you!

HVACNUT

If it's low voltage (24v) wire at the thermostat, then really no need to shut off the power. As long as you don't ground a wire to metal. 

The new thermostat is battery powered digital?

Are you sure it's not a faulty zone valve or something else? If you're looking to upgrade the thermostat anyway, fine. But it's a crap shoot as far as fixing the issue. 
"C'mon SEVEN! Baby needs new shoes!"

Joe Mattiello

Hi
youll have to find the power source for the ZVC controller to assure power supply to your thermostat has been shut down. It is 24 volts so it won’t harm you, but it may hurt the thermostat. I can’t speak to that because I don’t know what you’re using. It shouldn’t, 
if it’s a two wire thermostat simply remove the two wires from the old one, one at a time, and reverse the two steps using the new thermostat. Hopefully that resolves your issue.
if it doesn’t, I suggest calling Taco tech support at 401-942-8000 and have a technician support you.
hopefully, this was helpful 

jimmypenance

Thank you both for the responses! Sorry for the delay, I turned on email notifications but for some reason never got those!

So I replaced the stat with a new version of the same model (which I found out is a CT87K4446) since I read it might be a dead and un-replaceable battery. I just switched the new unit onto the already-mounted backplate. When I first did that I thought it fixed the issue, but a couple of days later I can't get the heat to engage at all. What's weird is the new thermostat also seems to be giving an inaccurate reading of the room temperature, and when I turn past that number, there's still no clicking sound at all.

It still seems like my apartment is the only one impacted.. but now it seems unlikely to me we have 2 bad thermostats in a row? So maybe an issue with the taco somehow after all? Appreciate any ideas

Intplm.

That T-stat should have a selection for the heat anticipator applicable to your system. Check to see if it is properly selected.

As too the click sound. The new thermostat might not make a sound.

A simple thing to try is jump the two wires together when you have the t-stat disconnected.Your heat should come on and stay on when you do that. If it doesn't then you have other issues.

jimmypenance

Thanks for the ideas! I was poking around the t-stat and I think I may have figured it out, and it's kind of silly... the wire into the thermostat is a little on the thicker side, and so the face came loose just a hair. But when I press in on it and turn the dial I can get the clicking sound to happen (which has something to do with the circuit being completed right?) and the heat comes on.

It seems like this is going to keep happening so I'll need to figure out a real fix, but at least the house is warm again!

It's interesting that you mention the selector settings on the thermostat... the old owners had the model set to "Hot Water, 90% efficiency Warm Air, Heat Pump (3 CPH)" .. when it seems like with our radiator set up "Steam, Gravity (1 CPH)" sounds closer to the system we have. But I figured maybe they knew something I don't... Think I should change the setting?

Intplm.

jimmypenance said:

Thanks for the ideas! I was poking around the t-stat and I think I may have figured it out, and it's kind of silly... the wire into the thermostat is a little on the thicker side, and so the face came loose just a hair. But when I press in on it and turn the dial I can get the clicking sound to happen (which has something to do with the circuit being completed right?) and the heat comes on.

It seems like this is going to keep happening so I'll need to figure out a real fix, but at least the house is warm again!

It's interesting that you mention the selector settings on the thermostat... the old owners had the model set to "Hot Water, 90% efficiency Warm Air, Heat Pump (3 CPH)" .. when it seems like with our radiator set up "Steam, Gravity (1 CPH)" sounds closer to the system we have. But I figured maybe they knew something I don't... Think I should change the setting?

You should change it to the type of system you have so the t-stat can work at its best.
It depends on your system described in the thermostats directions.

On your NEW thermostat on a (hot water system). Switch one OFF. Switch two On.


If its steam. both switches switched to on.