Nest gen 3 Hot water boost not working

[Eatkinson]

Hi,

I've had a Nest gen 3 thermostat for over 2 years now but recently I've noticed that the HW boost function doesn't appear to be working on demand, i.e. firing up the boiler. 

When I turn the 'boost' on via the app, or on the physical thermostat controller, I can hear a click on the heat link so I'm pretty sure the message is being received by Heat link. The Heat link appears to be fine as the Status light is green. 

When I manually override by pressing the central button on the heat link, all 3 lights are on and the boiler fires up.

I am struggling to diagnose the root cause.  

My first question is should I expect the "Heating" indicator on the Heat link to light up when the HW is triggered by the schedule?

Thanks in advance

[Paul_R]

Hi there @Eatkinson! I'm sorry to hear about this issue, but I'll do my best to assist you. To respond to your question, the Heat Link lights only change when you activate manual mode or in case of issues such as being disconnected from the display. The only signal that the Heat Link is being triggered is the click sound that you mentioned, otherwise the only light that should be on is the one green light. In order to establish what the source of the problem is, can you please answer the following questions for me?

What kind of boiler do you have, combi / system?

Are you able to activate the heat from the thermostat/app or it behaves the same as the Hot Water?

The Hot Water cannot be activated by the schedule either, or it is only the boost option that doesn't work as expected?

[Eatkinson]

Hi Paul,

It's a system boiler.

The behaviour is the same regardless of whether I use the app or the physical round thermostat control on the wall.

I think the schedule is working fine - it's just the boost.

[Paul_R]

Thanks for answering. From what you've told me, and the fact that the Heat Link clicks, it seems that the thermostat sends the signal to the Heat Link and the Heat Link also turns the relay, thus the click sound. I'd recommend getting an engineer to check your valve as it may be stuck. The manual mode probably activates the heating because it sends a stronger signal than a normal activation, and that may open the valve. 

[OannaCG]

Hello, just checking in, did you manage to see the message above? 

[Eatkinson]

Hi, thanks for checking in.  Just waiting for some input from my gas engineer

[OannaCG]

Alright, please keep me posted.

[Vladut]

Hi there, just checking in with you. Did you manage to check with the gas engineer?

[Paul_R]

Hi there! Since you haven't replied in a while, I'll have to close this thread. If anything else comes up, please feel free to reach out again. Have a great day ahead!