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Nest 3rd Gen learning thermostat S plan system

DaveM17
Community Member

I have a similar issue to the one community member Curtis1 posted 1 year ago:

"Just installed a S Plan system with a nest thermostat
Live Common to 2 and 5
CH on 3
HW on 6
When creating a demand for CH Both 3 and 6 are live
When Creating a demand for HW both 3 and 6 are live"

I have checked the wiring and have confirmed everything is correct but still the CH and HW are not controllable independently.

Any ideas welcome.

Thanks

DaveM

1 Recommended Answer

DragosC
Community Specialist
Community Specialist

Hi there, @DaveM17

Thanks for reaching out and thanks for the detailed description. That really helps. You'll need to perform a continuity test, not a voltage test. The continuity is more relevant as we need to see if the relays inside the Heat Link are communicating with the wires. Please follow the steps below:

  1. Ensure the relay switch is in the correct position by checking for continuity with feed Live and Neutral connected but all wires disconnected from the relay itself.
    1. When the Nest thermostat is calling for heat, check for:
      1. Continuity between 2 and 3
        • Yes - Correct
        • No - Incorrect
      2. Continuity between 1 and 2
        • Yes - Incorrect
        • No - Correct
    2. When the thermostat is satisfied, check for:
      1. Continuity between 2 and 3
        • Yes - Incorrect
        • No - Correct
      2. Continuity between 1 and 2
        • Yes - Correct
        • No - Incorrect
    3. When the Nest thermostat is calling for hot water, check for:
      1. Continuity between 5 and 6
        • Yes - Correct
        • No - Incorrect
      2. Continuity between 4 and 5
        • Yes - Incorrect
        • No - Correct
    4. When the thermostat is satisfied, check for:
      1. Continuity between 5 and 6
        • Yes - Incorrect
        • No - Correct
      2. Continuity between 4 and 5
        • Yes - Correct
        • No - Incorrect

View Recommended Answer in original post

10 REPLIES 10

Frustratedddd
Community Member

Your connections are correct at the Heat Link for a standard system boiler.

Easy way to test if the Heat Link is switching correctly, use a neon screwdriver, and check contacts 1 & 3, when calling for heat 1 should have no power, and 3 should have power. When not calling the oposite happens. The same test can be done with 4 & 6.

Do you have an oil boiler by any chance?

Can you show a picture of your connections at the Heat Link?

Thanks for the reply.

I have a gas boiler.

I have done the testing with a multimeter and can see the following:

With Heating off & HW off: 1 & 4 have power (correct)

Switch HW on ie Heating off & HW on: 1 & 6 have power (correct)

Switch off HW and switch on heating ie Heating on & HW off: 3 & 4 have power (correct)

Switch on HW ie Heating on & HW on: 3 & 6 have power (correct)

Switch off HW ie Heating on & HW off: 3 & 6 have power (not right - HW not going off as expected)

Switch on HW ie Heating on & HW on: 3 & 6 have power (correct)

Switch off Heating ie Heating off & HW on: 3 & 6 have power (not right - Heating not going off as expected)

Switch off HW ie Heating off & HW off: 1 & 4 have power (correct)

The issue is that when both HW & Heating are ON and either one goes OFF then the switching does not happen as expected.

Any ideas?

ThanksPXL_20221202_160008042.jpg

DragosC
Community Specialist
Community Specialist

Hi there, @DaveM17

Thanks for reaching out and thanks for the detailed description. That really helps. You'll need to perform a continuity test, not a voltage test. The continuity is more relevant as we need to see if the relays inside the Heat Link are communicating with the wires. Please follow the steps below:

  1. Ensure the relay switch is in the correct position by checking for continuity with feed Live and Neutral connected but all wires disconnected from the relay itself.
    1. When the Nest thermostat is calling for heat, check for:
      1. Continuity between 2 and 3
        • Yes - Correct
        • No - Incorrect
      2. Continuity between 1 and 2
        • Yes - Incorrect
        • No - Correct
    2. When the thermostat is satisfied, check for:
      1. Continuity between 2 and 3
        • Yes - Incorrect
        • No - Correct
      2. Continuity between 1 and 2
        • Yes - Correct
        • No - Incorrect
    3. When the Nest thermostat is calling for hot water, check for:
      1. Continuity between 5 and 6
        • Yes - Correct
        • No - Incorrect
      2. Continuity between 4 and 5
        • Yes - Incorrect
        • No - Correct
    4. When the thermostat is satisfied, check for:
      1. Continuity between 5 and 6
        • Yes - Incorrect
        • No - Correct
      2. Continuity between 4 and 5
        • Yes - Correct
        • No - Incorrect

DaveM17
Community Member

Hi @DragosC,

Thanks for your reply and recommendation for further testing.

I have done what you suggested with the relay wires disconnected. The results are as expected:

  1. When the Nest thermostat is calling for heat, check for:
    1. Continuity between 2 and 3
      • Yes - Correct
    2. Continuity between 1 and 2
      • No - Correct
  2. When the thermostat is satisfied, check for:
    1. Continuity between 2 and 3
      • No - Correct
    2. Continuity between 1 and 2
      • Yes - Correct
  3. When the Nest thermostat is calling for hot water, check for:
    1. Continuity between 5 and 6
      • Yes - Correct
    2. Continuity between 4 and 5
      • No - Correct
  4. When the thermostat is satisfied, check for:
    1. Continuity between 5 and 6
      • No - Correct
    2. Continuity between 4 and 5
      • Yes - Correct

So there appears to be no problem with the Heatlink setup and the issue is with some aspect of the external wiring that was possibly there before the Nest was put in but I never noticed.

Thanks again for your help in confirming the Nest/Heatlink setup.

Dave

AndaD
Community Specialist
Community Specialist

@DaveM17

No worries, this is why we're here. I'm sorry to hear about the issues with the wires. Hopefully it will get sorted soon. Don't hesitate to text us again if you need our technical assistance.

DaveM17
Community Member

@Thanks @AndaD - the wiring issue is also identified and resolved.

FYI - The original wiring for the two 2-way valves was not appropriate for the Nest. Changed two wires over to permanent Live and everything is working perfectly now.

AndaD
Community Specialist
Community Specialist

@DaveM17,

This is great news. I'm really pleased to know this and congrats for handling this situation so well. I really appreciate the fact that you shared the solution to these kinds of circumstances, in this way more people will have the opportunity to learn more about the wires configuration. Let me know if there's something else I can assist you with.

AlexD
Community Specialist
Community Specialist

Hi, just wanted to check in. How has it been going so far? Let me know if you need any further assistance.

DaveM17
Community Member

Hi @AlexD 

All good thanks - no further problems. The CH & HW switching totally independently according to the Nest control.

AlexD
Community Specialist
Community Specialist

That is great to hear. I will go ahead and close down the thread. If anything else comes up, feel free to open a new one or reach out to us on any of our other channels. Have a great day ahead!