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I'm stumped; Circulator runs continuously; Bad Powerheads?

mitchd123 Member Posts: 3
edited August 2019 in Domestic Hot Water
Hot water, oil - 3 zone system, 1 circulator, taco powerheads - used for hot water in the summer.

Woke up this summer morning and heard the baseboards clicking and giving off heat. The digital thermostats were all in the off position. Found out the circulator is running continuously.

Turned off the furnace by the emergency power switch, and disconnected the #1 thermostat wires on all 3 powerheads to rule out a short or bad thermostat. Turning the furnace back on, I would hear the circulator relay click on and the circulator would run.

With all the thermostat wires still disconnected, one by one I started disconnecting the #2 & #3 wires from the powerheads and I thought I isolated it down to a single powerhead. When I disconnected this questionable powerhead and turned the power on, the circulator relay did not kick on. During this process of elimination, I made sure that I did not accidentally disconnect the transformer or circulator control wires.

What didn't make sense is the supposed bad powerhead was not in the zone that was coming on. So to double-check my work, I wired up only one powerhead one at a time. I wired up #2 and #3 to the transformer and circulator control wires. While testing, it appeared that now two powerheads are causing the circulator to run continuously. Is it possible, or could it be something else?

Testing with an ohmmeter further confused me. I thought 2-3 were supposed to show no resistance.

"Powerhead which doesn't run the circulator"
Pin 1 to 3 resistance
Pin 2 to 3 resistance

"Powerheads which do run the circulator"
Pin 1 to 3 no resistance
Pin 2 to 3 no resistance

The furnace runs fine, keeps temperature, starts and stops no problem. I've temporarily disconnected the transformer to keep the circulator from running.

Ideas? What else should I try?

PS, sorry for posting this in the wrong category...can't find a way to move it /delete/repost.


  • Steamhead
    Steamhead Member Posts: 16,835
    Where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Jamie Hall
    Jamie Hall Member Posts: 23,289
    You could have two bad end switches. If that were the case, either one would run the circulator -- but it could well be that the valve isn't open, just the switch stuck closed. That would behave exactly as you have described.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    rick in Alaska
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    Could simply be shorted low voltage wire. Not simple to find mind you.
    delta T
  • delta T
    delta T Member Posts: 884
    do you have a combination aquastat relay on the side of the boiler?
  • mitchd123
    mitchd123 Member Posts: 3
    Thanks everyone for your help. I really appreciate it. I'm trying to figure out what to try next.

    @Steamhead (in transit) I'm in RI. Circulator wasn't wired to run fulltime as some are in Canada. I hope. :-)

    @STEVEusaPA - Thank you, I have 23.6v at the transformer with the zone valves disconnected. I do have another transformer I can try, but I would think too low voltage would not make the circulator relay engage.

    @delta T Honeywell combined aquastat. It's probably pretty old. I've attached a pic.

    Some additional details, The house & furnace are around 50 years old, I've lived here 20. Many parts have been changed over the years, burner, etc. Most recently about 9 months ago I replaced the circulator. (2nd one in 20 years). Also for the past few years, on very rare occasions, the bedroom zone would run too long. Instead of shutting off at 70, it would occasionally run up to 74 degrees or so. Turning off the thermostat really didn't seem to have an effect, but it would always solve itself. The valves seem to be original valves, but I'm assuming the heads were changed through the years. I RI we don't have any issues with sediment build-up like other parts of the country. I checked the valve with a big pair of pliers with the power head removed. It seemed to move freely and wasn't getting stuck. I assumed the powerhead was getting tired, and replaced it about two years ago with another spare I had on the bench.

    I guess I'm going to need at least 1 powerhead, maybe 2, and possibly an aquastat? Glad it's now and not in the middle of a blizzard.

  • hot_rod
    hot_rod Member Posts: 22,143
    You really need a volt meter to track down a wiring issue like this. No reason to replace parts until you determine the cause.

    If power is on the ZV all the time, somehow somewhere there is a call for heat or shorted wire.

    There is line voltage, 120V under that cover, be careful!
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mitchd123
    mitchd123 Member Posts: 3
    Thank you ALL for your guidance and excellent responses. I finally got a chance to work on the system and it seems I have two zone valves which are failing. I put an indicator light on the circulator to help troubleshoot this.

    My Taco zone valves heads take about 45-60 seconds to open. One of the troublemakers takes over 90. (Taco gold head / 572 body) Once thermostat power is removed, even after 5 minutes I'm still getting continity between pins 2 & 3 and the circulator's running. Removing the powerhead, it continues to show continuity between pins 2 and 3, until I can push the head back with my finger which will break continuity. The valve body that it's operating on, starts making a loud vibrating noise as the valve opens and closes. I swapped in another good powerhead, and it operates correctly, but it still makes noise during operation. I'm guessing the guts of the 572 valve body need to be replaced. I've not done one of these before, but I realize it means draining the system, purging, etc. Not trying to start a holy war, but should I just replace the guts with a new Taco 572, or consider a newer style/brand?

    The other powerhead which is sticking is a old round Taco 541 zone valve. Circa early 1970s, even after 3-5 minutes it won't turn off until I bang it gently with a rubber hammer. Are parts even available? Or do I replace with a newer style valve?

    After the valves are replaced, and I'm ready to purge the system, should I be adding anything to the water to lubricate/preserve these valves/boiler, etc??
    EBEBRATT-Ed Member Posts: 15,525
    Those Taco valves are not my favorites. You could try Erie or Honeywell
  • rick in Alaska
    rick in Alaska Member Posts: 1,457

    Those Taco valves are not my favorites. You could try Erie or Honeywell

    Or Taco Sentry"s. Very low power requirement, quick open, quiet, easy to wire, easy to change, and led indicators.
    I can't believe you can get a Taco 555 to open in 90 seconds. I find it is usually closer to 2-3 minutes.
  • hot_rod
    hot_rod Member Posts: 22,143
    Or Caleffi if you want the very best spring return style.

    Press tailpieces make for a quick and easy swap.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream