Thermostat stuck to 'on'

[aclark7]

My boiler appears to be on permanently at the moment, even when everything has been set to off on the Nest thermostat.

I have tried restarts of both the thermostat and the heat link, but this has not worked.

The only thing that appears to turn the boiler off at the moment is to remove the Nest thermostat from the wall!

Any ideas? Thank you

[jenniffert]

Hi aclark7,

Thanks for reaching out to the community! I understand that your boiler is running continuously, even when your Nest Thermostat is off, and removing the display is the only way to shut it down. I appreciate you sharing the troubleshooting steps you've already attempted. No worries, I’d be happy to help!

To better investigate this situation, I’d like to ask for the following information:

• What is the specific model of your Nest Thermostat? Here’s a helpful article about how to identify your thermostat model.
• When was the thermostat installed?
• When did the issue first occur?
• What color is the LED status light on the Heat Link?
• Is there a wiring report or error message on your thermostat or app?
• Have you had any recent maintenance done on your electrical or heating system?
• Were you experiencing the same behavior with the previous thermostat?

I look forward to your reply.

Best regards,

Jenniffer

[aclark7]

Hello Jennifer, thank you for replying. I hope that you can help me.

To answer your questions... 

• The model is Display-3.4
• It was installed approximately 7 years ago
• The issue first occurred last week, shortly after a software update
• There is a green light on the Heat Link
• No error messages have appeared
• I have had some maintenance on my heating system; the diverter valve was replaced on the hot water tank as the heating came on at the same time as the water was heated, even though the heating was switched to off. Everything worked fine for about 5/6 weeks before this new issue arose
• I have never experienced this issue before, either with this thermostat or a previous one

In addition to removing the thermostat from the wall to fix this problem, I have found that performing a 'factory reset' also fixes it. However ... after this, it only behaves itself for about 24 hours, switching the boiler on and off at the programmed times, before it switches itself back on permanently again.

I have just removed the thermostat off the wall again as I don't want my water heated permanently throughout the night!

Please help!

[jenniffert]

Hi aclark7,

Thanks for following up! I appreciate you sharing these important details.

To move forward, please make sure you're near your Heat Link and have the Nest app open. We'll start with a simple test:

• Use the Nest app to turn on the heat or hot water.
• Listen carefully for a clicking sound from the Heat Link.

Please perform a click test on each relay individually. This will help us determine if one or both relays are stuck in an always-on or always-off position.

Keep me updated.

Best regards,

Jenniffer

[aclark7]

What do you mean by 'each relay individually '?

[jenniffert]

Hi aclark7,

Thanks for your reply! 

Testing each relay individually means that the heating and hot water relays must be assessed as separate components. The Nest Heat Link has two main relays:

• Relay 1: Controls the central heating.
• Relay 2: Controls the domestic hot water.

A correctly installed Nest Heat Link with a functional boiler and proper connections should produce a distinct clicking sound when the heating and hot water are activated and deactivated.

Please keep me informed of the test results.

Best regards,

Jenniffer