Taco Zone Valve

Discussion in 'HVAC Heating & Cooling' started by emaciat0r, Dec 29, 2008.

  1. emaciat0r

    emaciat0r New Member

    I live in a condo and have floor board hot water heating systems throughout. The system is hooked up to a heat only thermostat and is 24volts. I am having problems with the system and could use some advice. I've checked for power at every point in the system and I have appropriate power everywhere. The problem is that the system does not seem to be responsive. What I mean is that the system seems to be heating but at a very low capacity. I turn up the thermostat and it doesn't heat past a certain temp (about 70 degrees Fahrenheit). I assumed that the problem was the zone valve head so i ordered a new one and proceeded to change it, following the directions precisely. The pipes for both the input and output are extremely hot (i can only hold them for about 10 seconds before i need to let go). Also, i use to hear the valve or something related to it click every half minute or so. Now it doesn't make a noise what so ever. Any advice would be great.

    Thanks, Raymond
  2. helix3

    helix3 Sr. Systems Engineer, Biotech

    A meter is your friend

    I just replaced a dead Taco power head the other day. The 'clicking' that you hear is a mechanical switch inside the valve. It is what sends the signal to the boiler that heat is being demanded. When your thermostat is requesting heat, it may take up to a minute for the zone valve to actually open. If you have hot pipes on both sides of the valve, it would sound like it is working, but if the signal from the valve may not be getting to the boiler, your circulator pump won't know to turn on.

    Easiest to troubleshoot with a meter. Measure the current from the thermostat to the valve. You should have ~ 1 amp when the thermostat is demanding heat. Once a steady-state is reached, the current will change between zero and ~1 amp every few seconds. This is the servo-action of the valve. If that is working ok, then check that the signal from the power head is getting to the boiler that tells it heat is being demanded.

    If you have a lever on the power head, flip it up towards the pipes. This will manually open the valve and manually activate the switch. At this point, your circulator pump should be running and hot water flowing.

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    Last edited: Dec 30, 2008
  3. nhmaster

    nhmaster Master Plumber

    S. Maine
    Jumper between terminals 2 & 3 and see if the circulator starts. If not, you have a problem with the circ relay. If it runs you have zone valve problems, or the thermostat has a burned out anticipator which btw should be set at .9amps
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