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Grundfos pump controller relay clicking on and off with Nest...

I am installing a new system and when I jump the R W on the pump controller, it works fine. When I use an old Honeywell thermostat, it works fine. When I use a Nest, It comes up, but then at random intervals ranging from every few seconds, to 30 seconds or more, the relay clicks off for a second, and then on.

I didn't install the Nest myself, but it must get it's power from the AC condenser, as the hydronic heat wire is only two wires. Also I suppose it can get power from the RW of the heat to charge itself, but I suspect it does get C wire power from the AC controller since the heater transformer has been turned off for many weeks and the Nest stayed powered up.

Any idea why it is clicking off and on, and what the fix is? A bleeder resistor?




Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,913
    edited October 2022
    Have you always had this issue?

    Nest thermostat gets powered from Rc and C. If you are using Rh and W1 for operating that multi zone relay, there should be no problem. However the Nest does not use conventional switching contacts in the thermostat. There is some type of lowering and increasing of resistance between the R terminals and the other letter terminals. That said, your Zone controller may not like that and will require the addition of a resister. Call Nest tech support and have all the part numbers available for the zone controller pumps and air handler. Also have a multimeter available. After you talk to the first tech support person there and they are unable to solve the problem, they will bump you up to the real technicians that can help. Time consuming I know, but this is the way the tech world works.

    If all else fails, an isolation relay will work.
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • rsilvers
    rsilvers Member Posts: 124
    "Have you always had this issue?"

    I am installing a new system. This is happening for the first time, during the install. It worked fine on the old zone relay that I removed.

    Yes, the first tech person can never help me. If they could, the problem would have been simple enough that I could have fixed it myself.

    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,913
    Agree with you @rsilvers. There are many different parts that can be used to solve this. I really like having the RIB brand of relays on the service truck at the end of my service career. The R8222 and R4222 relays were my GoTo relays before that. look at this discussion I just helped with for another way to use an old style "Fan Center". Price is about the same as purchasing the transformer and relay separately (under $30.00) https://forum.heatinghelp.com/discussion/189342/thermostat-losing-power-lwc
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,913
    edited October 2022
    What I dont get in the Zone Control is that there are thermostat wires to zone 2 and zone 4. There are circulator pumps wired to Primary Pump P and Pump 4. There is no pump associates with zone 2 ????

    Someone has done some serious control engineering to get this system to work (if it does). Looks like Primary Pump P will operate on a call from either thermostat. Primary pump 2 and pump 4 will operate on a call for heat from zone 4 thermostat. In that scenario, zone 2 will heat when ever zone 4 calls for heat. Not sure why someone might need to do that.

    But If it ain't broke... don't fix it.

    However if the thermostat attached to Zone 2 on the zone panes is in a room that is overheating regularly, then there is a good chance that the system needs some "control wiring" attention
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • rsilvers
    rsilvers Member Posts: 124

    What I dont get in the Zone Control is that there are thermostat wires to zone 2 and zone 4. There are circulator pumps wired to Primary Pump P and Pump 4. There is no pump associates with zone 2 ????

    Because I took the photo after I hooked up the thermostat wire to zone 2 and before I hooked up the pump to zone 2. As I said, I am installing a new system. Like installing it right now.

  • rsilvers
    rsilvers Member Posts: 124
    I called Nest and as soon as they asked me to log into my google account to verify my ID, I decided I can't deal with customer service at google. I hung up.

    I ordered some 5 watt 500, 1000, and 2000 ohm resistors to see if putting one across W and C will solve the issue.
  • rsilvers
    rsilvers Member Posts: 124
    edited October 2022
    Won't have resistors until Tuesday since hard to get these large ones quickly. Will jump the zones for now to test. In the meantime, the I connected the fuel and the new boiler started.