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Taco Zone valve troubleshooting. Heating issue...*

ShacharShachar Member Posts: 36

Sorry if this discussion is showing twice. I posted this question, then after posting the table I created did not show up properly, so I edited it and saved, but then the discussion disappeared. If the previous one shows up, I'll delete/close it to avoid duplicating of it.

I tried searching the forums, and searched google for answers, but didn't find an clear explanation of the following:
I have hot gas/water baseboards for heating, 2 zones, and Taco valves.
Heating for zone 1 does not work properly. Seems that during the day it's not heating at all and zone1 temp is around 63F even if I set the thermostat to 69 or 70.
At night the temp in zone 1 is about 68. outside it's actually colder (24F) so I don't know what's going on.
Trying to troubleshoot this to see if my zone1 valve is defective, or maybe the transformer or the wires.

I tested with voltage meter and these are the readings:

Thermostat ON Thermostat OFF
Screws 1&2 2&3 1&2 2&3
Zone1 21.4V* 25V 0 25.1V
Zone2 24.4V 0 0 25V
Zone1Only 22.5V 24.5V
Zone2Only 22.5V-24.5V 24.5V
When Zone2 Thermostat is ON then Zone2 manual Valve opens all the way if I pull it.
When Zone1 Thermostat is ON then Zone1 manual Valve goes up just a quarter of the way if I pull it.

*Another time I tested Zone1 with Thermostat ON Voltage was 19.4V-21.1V

Note: When Zone2 Thermostat ON then Zone1 2&3 showing 0 volt. Tested this twice.

Thermostat for Zone1- tested wall wires = 24.5V. Tested Thermostat itself for continuity when ON = YES, when OFF = NO continuity.

Can anyone please help shed light on what is going on?
I got a new Taco zone valve from the store, but I want to understand all this before attempting to install it to see if it resolves the problem.

I can attach pictures of the transformer and the valves, but I believe this is enough info.



  • SteveSanSteveSan Member Posts: 75
    Good morning Shachar, please call Taco Tech Support today. We are here from 8am-4:30pm EST and can help you with your issue.
  • SteveSanSteveSan Member Posts: 75
    Shachar, phone # is 401-942-8000
  • HVACNUTHVACNUT Member Posts: 3,710
    Sounds like a simple zone valve motor needs to be replaced.
    rick in Alaska
  • ShacharShachar Member Posts: 36
    Thanks SteveSan. I called and talked to Ben from tech support. I explained the issue over the phone. He said that most likely I have air in the system for zone 1 that doesn't work and I should try to purge the air out of the system. Was that your reasoning too...?
    According to him the voltage readings are fine and the Taco zone valve will open for any voltage over 19 point something (don't remember exactly what he said).

    I'll try to purge and see if there is any difference.
  • SteveSanSteveSan Member Posts: 75
    Ben is correct Shachar, sounds like you have an air issue and all of your readings are correct. Valve only needs 19 volts to open.
  • NY_RobNY_Rob Member Posts: 1,370
    You could manually open the zone valve on a call for heat... if you get heat at that point it's a bad ZV, if you still don't get heat it may be air.
  • HVACNUTHVACNUT Member Posts: 3,710
    If you have 24v to the zone valve but you say you have to manually open the valve, it's a bad ZV motor or linkage.
    Like @NY_Rob said, you can lock the lever manually open and that zone will heat whenever the other zone calls.
    Replace the actuator head.
    rick in Alaska
  • ShacharShachar Member Posts: 36
    Thanks all for the useful suggestions.
    I did manually opened the zone1 valve while the thermostat was ON and it did start to heat properly.
    I then replaced the valve with a new one I got from the store ($75) and tested again, and it works now. So I guess it was a bad zone valve. I did notice that for screws 1&2 when it thermostat is on there is about ~22V until the valve fully opens and the heating starts, then it's ~24V+ - why is that?

    Anyway, thanks again for the help in troubleshooting. The wife is happy now :smile:
  • Mook531Mook531 Member Posts: 8
    once The valve opens, and the heater that opens the valve is disengaged, the amperage applied to the valve goes down, so voltage goes up. Once it needs the heater back on, amperage goes up, so voltage goes down. Only usually have 40 va....use it wisely 😁

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