Troubleshooting a Taco Zone Valve: Checking the Voltages

Some background: I have a forced hot water system with five zones. One of the zones wasn't working and I had to debug the system without having much knowledge of plumbing & heating. I took the wires from a working zone valve and put them on the non-working valve and the valve worked, so that meant the trouble was with the electric circuit in the zone. A little research helped me find out that when the thermostat calls for heat, 24 volts is sent to the zone valve and can be measured using terminals 1 + 2 on the valve head. If you don't get 24 volts, then there's a break in the system that could be the thermostat, the wire, or the transformer and I wasn't getting any voltage. I measured and got 25 volts at the transformer so that was okay. That left the thermostat or the two-wire cable from the thermostat to the furnace. I tried another thermostat and that didn't make a difference, so it was something to do with the cable. I had to trace the wiring through a spaghetti-like maze of wires and found that the red wire that goes from the thermostat at the RH terminal to the transformer at the R terminal was loose at the transformer. I tightened it up and turned up the thermostat to call for heat, measured the voltage and there it was.

[hmdwn]

This doesn't prove the valve is bad, it only proves the thermostat (when on) is sending 24 volts to the valve, and that's it!
I just experienced this, I had 24 volts to the Taco zone valve, the circulator pump would come on however, the boiler burner would not fire. The end switch in the zone valve was bad terminal #3 did nothing.
I replaced the Taco power head and it and the boiler operated as should.

[lisav]

Thank you for the clear and concise checking of the zone valve function. I truly appreciate you giving the details of a Camera you used in producing this video. TY

[rrpo]

just because you get votage to a zone valve, that doesn't mean the valve woks.

[robertkoretsky]

If you have two or more of them on your manifold, just switch out one you know is good for one you suspect is bad to test! And they’ve gone up in price 100% in just a few years, to ensure that the Taco owners can continue to vacation in a high priced resort.

[newyork]

gread video tnx, gave an idea to bring my thermostat down to the boiler and test all there, instead of running up and down the stairs scared that Transormer is burned again =) tnx man

[eastcoastHVACtech]

You need to see 24v across terminals 1 and 3 to prove the end switch is closing, you can have voltage all day long on 1 and 2 but you won't have heat of the end switch isn't closing.

[kellybaa]

Thanks for the helpful video. It was clear and easy to follow. It helped me figure out what was going on with my zone valve. In the end it was a dead thermostat. Thanks!

[copkhan]

Step#1 Turn the thermostat on and check the voltage across #1 and #2, it should read 24 volts.

Step#2 Discount the wire from terminal #3 and now check for continuity between terminal#2 and #3 using Ohm meter. If Ohm meter reads 0 the valve is good and if you see infinity or an open circuit the valve is bad.

[ryanbard]

All you did is confirm that the zone valve is receiving voltage... That tells you nothing about the zone valve. It just tells you that the thermostat is working.... 🤦

[stasiawierzbicki]

How is this a troubleshooting video when you don't explain what to do when it isn't working correctly?

[John-xxzj]

if zone valve woldnt be working how wud u know if its zone valve or faulty thermostat?

[johngallati]

AS HE PUTS HIS HANDS IN FRONT OF THE METER

[johngallati]

AND HE DIDNT FINISH THE TEST THERES MORE TO IT.

[jeffreylonigro]

Am I understanding this: no call for heat is 22v and heat call is 25v? That doesn’t sound right.

[mortsdans]

You should also check resistance across 2 and 3. Dial the thermostat up after being off and watch it. After a minute or so of power the resistance should drop to nothing and your boiler turns on. Turn the thermostat back down and it should reverse after a while

[mohawkmike]

Thermo off 22 v thermo on 25v..where did the 3v come from? wish I hadn't watched this video.

[jaybaar]

Great video, very helpful thank you! Why do you think I would have 25 volts with boiler and all t stats off as well? Happy Thanksgiving! 🦃

[jimbo]

Hey, that's great. Glad it helped someone.

[jeffjohnson]

stupid video  to do this correctly you also should be showing what one that was not working read for voltage.  also should have identifited the voltage on terminal 3.  nice try but not enough info

[bostonkid]

Isn't the arm on the valve supposed to move?