Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Taco SR504 EXP constantly cycling

Hi everyone, I have a taco SR504 exp that is hooked to 4 zones and my hotwater heater. Over the last two weeks I have noticed that it is cycling on once every 5 minutes for about 10-20 seconds each time, all 4 zones turn on at the same time and cycle. The lines run through the entire house through the tile floor and I noticed the floor was warm even thought all the thermostats are turned off as it is summer. I cannot find any information on one cycling this often, I thought they typically cycled once ever 24 hours, or once every two weeks, but this is every 5 minutes for all zones. Has anyone experienced this? Thanks in advance.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    I’d try disconnecting the thermostat wires from all zones except the indirect. If it still happens you probably have to replace it. Seems like it may have taken a voltage spike.
    HVACNUT Member Posts: 5,841
    edited July 2021
    Check the dip switches. I don't have much experience with the EXP but I see pump exercising and time intervals there.
  • Joe Mattiello
    Joe Mattiello Member Posts: 706
    Disconnect all thermostats including indirect and methodically put them on proving out each zone until you discover the problem.
    I’m confident it’s not the control. SR is robust and in my years of diagnosing it’s usually a thermostat or aquastat.
    if it persists, contact Taco Tech support at 401-942-8000 and ask for tech support.
    hopefully this helps:-) 
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions
  • Falkor
    Falkor Member Posts: 2
    Unfortunately my SR is an older unit and it does not have the dip switches shown in the schematic above. I disconnected all of the thermostat wires and it still cycles for 30 seconds every 5 minutes. I will call tech support as Joe recommended, it is an older unit that was installed in 2003 so I would not be surprised if it needs replaced. Thanks.