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One Zone Stopped Working (troubleshooting ideas or call a plumber?)

I have a tankless oil water heater with 4 zones (2 up 2 main level) of baseboard heat. Just yesterday one zone stopped working. Baseboard is cool and both ends up pipe are cool in this zone.

I checked the temp on what I believe are the return pipes for each zone and they are all 100+ degrees.

My main question is how do I troubleshoot whether I have a thermostat issue or something else? As part of an energy audit by Mass Save a month+ ago they put in a timer thermostat in the zone affected. I could try putting back the old thermostat.

I've read several other posts and have heard about possible frozen pipes, air in the system, etc, so wasn't sure where to start. I'm probably not comfortable doing anything to my system that requires emptying the water, so I may be in the 'call a plumber' category. Thanks!

Some pictures of a few pieces of the system attached if that helps.



  • pipeking
    pipeking Member Posts: 252

    i'm going to give u an easy way off testing, take off that thermostat (is it a heat only thermostat) and connect the red+white wires together, i like to use a wire with an aligator clip on each side. u should have heat within 5-6 min, if not then your zone valve needs attention
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    you most likely dont have a water issue

    It's probably something on the wiring/control side.  Could be a bad zone valve, or some other control.  Without knowing what other components are on your boiler, your best bet would be to call a qualified oil tech to come out and do the basic troubleshooting.

    Regarding the thermostat, if the room temperature is below the set point temp, and the thermostat is not indicating a call for heat, then you can start at the thermostat.

    I have a customer with a similiar "energy saver" thermostat from the utility company, that was having a problem.  After talking to the utility company, they told me, the customer should call the utility company, they will come out for free and check the thermostat.  If it is bad they will replace, if not bad, tell the customer to call their hvac company to repair the system

    There was an error rendering this rich post.

  • icesailor
    icesailor Member Posts: 7,265
    Third World Trouble SHooting:

    Try this.

    See that god zone valve in the second photo, look on the left side, to the left of the terminal strip. See that lever that is near the top? pull slightly down. It should stop or get hard about 1/2" down. Go turn all the thermostats up as high as they will go. Wait five to ten minutes. If you find that one zone isn't getting hot, check all the hot ones. That lever will easily come all the way down to the bottom of its travel. Try the one that is cold. Does the lever only travel a short distance? If it does, the power head may be bad. You should get a pro to check it out. If you try t yourself, be sure that you kill all power to the system and first remove the top, red wire from the power head.

    If it turns out that the zone that isn't working and it is the zone with the electronic thermostat, Taco and others actually suggest an isolation relay to power the thermostat and the valve. It needs the full voltage to run properly.

    If you try it yourself, follow the instructions. Remove the red wire. Go have a cup of coffee, come back and remove the rest of the wires. If you notice any small sparks arcing, there is still power to the valve.
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