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Running two circulators from a TACO SR501 Relay

I have a AO Smith GT15C-540-NI (similar I think as a TK-540P-NIH) gas tankless water heater. I have a one zone hydronic floor system (on a single manifold with three small loops) . I have a Honeywell thermostat. I have a fluid heat exchanger. I have a circulator on one side with 3 small radiant floor loops. I have a mixing value for domestic water on the hot water heater, some of which which can travel to the heat exchanger. Both loops (radiant floor side of heat exchanger and heater side ) have circulator pumps. This is how the water heater suggests plumbing. Both pumps are Grundfos 1/25 hp .7 amp pumps. I'm wondering if I can wire both pumps in parallel on a SR501 one zone relay. In simple terms the thermostat when needed should have the water heater pump running to bring heat to the heat exchanger, and the radiant floor pump should take the heat from the heat exchanger to the floor until the thermostat stopse calling for heat. Any help or advice will be most appreciated.


  • hot_rod
    hot_rod Member Posts: 21,820
    Should be at least a 5A, maybe 10A relay in that control, fine for two small circs.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Hithere
    Hithere Member Posts: 3
    Thanks Hot Rod! I had looked everywhere but could find anyone doing what I was wanting. That is what I recall reading somewhere else some time ago. I didn't want to hook things up and find it wasn't going to work My electrician had suggested I could hook everything up and he would check it over beforehand. BTW I don't have any boiler connections so I'm assuming the TACO SR501 one zone relay will work without them being connected. If you are in the US Happy Thanks Giving! t
  • GroundUp
    GroundUp Member Posts: 1,865
    Yes, but is the 15-58 big enough to circulate the water heater?
  • Hithere
    Hithere Member Posts: 3
    Hi GroundUp, I am using Grundfos 59896155 and see others have used similar circulators in similar setups. Thanks for the comment. t