The setup:

  • The system is a 2-zone system. A. Zone 1 heats the garage floor B. Zone 2 heats the main living quarters upstairs
  • The water is heated by a Takagi Tk-2 tankless water heater. The controller is a *Nix Technology SP82/SP83.
  • I contacted the company that bought out Nix Tech. They said that controller was 17 years out of production. They recommended replacing it with an iLink SP83

The problem: When testing the floors for proper operation (I test once a year because we heat with wood) the heater turns on / the pump fires up and both run for about 15 seconds, then shut down. This happens with BOTH Zones. The call for domestic water heats just fine.

Upon removing the controller cover it seems (I don't know because I don't work on or know this stuff) the previous owner wired in a 3rd relay to handle the domestic water heating action (my guess). If it had been a standard setup I would attempt to do it myself. But because it isn't I'm hesitant to mess with it because if I screw it up and the domestic side stops working I'm in a world of hurt.

The fact that BOTH floors do not heat but the domestic side DOES leads me to believe that the problem is common to both floor a) relays or b) the transformer.

I have a plumber coming out on Monday [tomorrow] that is supposed to know how this type of system works, We'll see.

  • 1
    Can you provide any photos of your system? Hydronic radiant systems are often quite simple once the key design effects are clear. For example are your zones controlled by valves, pumps, or both? Do you have a primary/secondary loop? What thermostats,? Photos should help.
    – Matthew
    Feb 26 at 6:16
  • 1
    While Ecnerwal often provides very good answers, nobody knows what you're thanking him for. If this is in relation to another question here, please edit this question to include a link to the other one. You can right-click the Share text under the other question, then copy the link location. Once you've got that, edit this question and paste the link in so we all know what you're talking about.
    – FreeMan
    Feb 26 at 14:14
  • Please revise your title to ask a clear, specific question and not just state that you have a problem. Make it more informative.
    – isherwood
    Feb 26 at 15:20
  • I’m voting to close this question because there is no question asked.
    – FreeMan
    Feb 28 at 18:08

1 Answer 1


Problem solved. Defective thermostat.

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