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

Switch Relay/Circ Pump not listening to Stat

Heat_newbHeat_newb Member Posts: 1
Hello -

I have a Weil-McLain P-WTGO-6 (Series 3) Oil-fired Water Boiler running baseboard radiant. I have a Taco SR504 Switching Relay running 4 Zones.

My issue is that zones 3 and 4 don't seem to be listening to their stats. Despite their set points being satisfied, the zone stays lit (RED zone indicator light) on the Taco, and I can hear the Circ Pump and furnace continue to run. They will continue to run in this manner even if I turn the Stats OFF. The only way I have been able to get it to stop is to disconnect one of the Stat wires where it comes into the respective zone on the Taco.



  • hvacfreak2hvacfreak2 Member Posts: 500
    Does your unit have 2 or 3 terminals for each thermostat input ?

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

  • JohnNYJohnNY Member Posts: 2,591
    Remove the thermostat wires and jumper the T-T (or end switch) connections on each zone. If doing that energizes the pump terminals and closes the X-X contacts, then your problem is in your thermostat/wiring.
    For troubleshooting and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is the Boilers and Hydronic Heating Systems Course Instructor at NYC's Mechanics Institute, a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
    For residential service and installations in New Jersey, please see Toro Plumbing & Mechanical and fill out our contacts page, upload pics, and submit, or call (973-672-1000).
  • hvacfreak2hvacfreak2 Member Posts: 500
    Either way the question is weather or not voltage is present on the input wires. If it is a 2 wire input remove one of the wires and measure it's voltage to 24 volt common ( power input toward the left of the relay board has a common ). If there is no voltage present on that wire than I would suspect the relay board. If there is voltage present than the problem is in the wiring or the thermostats. If this is a 3 wire input use the W wire for testing.

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

  • HVACNUTHVACNUT Member Posts: 3,707
    Are the thermostat wires for 3 and 4 from one cable? For example, zone 3 has red and white and zone 4 has green and yellow and they're from one cable and then split somewhere to there respective stats?
    With 2 zones constantly running but stop when you disconnect a wire from TT, it seems like a dead short on a 4 (or more) conductor cable. Hang any pictures lately? Or any work using nails or screws?
  • ratioratio Member Posts: 2,694
    What stats are on the zones? Stats that use TRIACs to switch loads, as opposed to a relay, can fail conductive, analogous to the contacts of a relay sticking closed. They can also fail conducting in one direction only, i.e. appear in-circuit as a simple diode. They also are somewhat hard to diagnose, as they require a minimum load on the output side to operate—a modern high-impedance multimeter will show them as conducting regardless of the state of the device. A meter with a low impedance range, like the Fluke 116, will give you valid readings.

Leave a Comment

BoldItalicStrikethroughOrdered listUnordered list
Align leftAlign centerAlign rightToggle HTML viewToggle full pageToggle lights
Drop image/file


It looks like you're new here. If you want to get involved, click one of these buttons!