Nest Thermostat E Heat Link damaged boiler

[Maurio]

I had an issue with my heating the other day where the boiler was not switching on when told to by the best thermostat E.

an engineer has looked at it today and confirmed that the PCB on the boiler failed. He noted that the thermostat e heat link was putting out 120 volts to the boiler at all times, increasing to 230 volts when heating was demanded. The heat link should have been inputting 0 volts when demand is removed. He believed that the heat link putting 120 volts out to the boiler at all times is what has caused the PCB in the boiler to fail, potentially due to a part in the heat link going wrong.

Is this an issue that anyone has encountered before? My thermostat is out of warranty so I would like to replace it but I don’t want the same issue to happen again.

[AlexD]

Hi, thanks for reaching out to us here @Maurio . I am sorry to hear you are facing difficulties with your system and I would be happy to try and assist. 

Voltage leak can be measured in the Heat Link relay but that does not meant that there is actual continuity through it. Regardless, that should not affect the boiler as 230V or any other amount will not  directly into the boilers PCB. And even if it did, in a very cold period where the thermostat would keep your heating always on, it would have a constant flow of 230V. So it is unlikely that 120V, even if it was provided, would affect the boiler as it is designed to receive 230V most of the time. It is more likely that a component from the boiler failed.

Do you still have the Heat Link at the location? There are a few things we can check together to see if we can narrow down what may have occurred. Also, how long has the thermostat been installed for and working before this occurred? 

[Maurio]

Yes, the heat link is still in place though the plumber has recommended I remove it when the new PCB is installed. He said the heat link should be giving off 0 volts when no heat is being demanded, is this correct?

The thermostat has been installed and working for 3 years prior to this.

[AlexD]

Thanks for the information. There can be voltage leaking in the thermostat relay so the voltage will not necessarily be 0. What we would need to check is the continuity. If you have a multimeter and are comfortable in doing so or can get the installer to check it I can send you an email with instructions on all the steps to check it. 

Would it be ok if I reached out over the email associated with your account here with more information? 

[Maurio]

Hi Alex, yes that would be fine, thank you.

[UanaC]

Hello there @Maurio! I've just sent you the email my previous colleague told you about. Let me know when you've replied to it.

[Maurio]

Hi @UanaC , thank you. I have replied with the information. You will get two replies, in the first one I forgot to include the number that was requested in the email. The second reply should be correct. Let me know if you need anything else.

thank you.

[AlexD]

I sent the email your way with the steps. Let me know once you've gone through them and reply to my email with the results. 

[Maurio]

Thank you @AlexD I have the email.

i don’t have a multimeter so I’ll need to see if the engineer can do the test. Could you please advise what results would be indicative of an issue and what results would indicate normal operation so I can verify with him whilst he is here if he can do it?

The engineer’s concern was that the boiler would have been consistently getting a 120 volt demand and this would have caused the PCB to break down as it wasn’t sure if heat was being demanded or not.

[AlexD]

The expected behavior would be to have continuity between C and FP and no continuity between C and NO when the heating is off and continuity between C and NO and no continuity between C and FP when the manual mode is active. If this is that case that would indicate that no power is being sent when the heating is off as the internal relay switches between NO and FP depending on the demand. 

[Paul_R]

Hello! Have you managed to check my colleagues previous message?

[Maurio]

Hi @Paul_R , thank you for following up.

the engineer has just checked this today. He replaced the PCB on the boiler and the Nest was still not functioning to turn the boiler on. He then fitted a standard thermostat and the boiler was working fine. He therefore didn’t do the continuity test as the heat link was clearly not functioning correctly as even in manual mode it wouldn’t turn the heating on. So it seems that the PCB in the boiler failed and then caused the Nest heat link to fail, or vice-versa. It looks like I require a replacement heat link for my Nest Thermostat E.

[Paul_R]

I see, in order to process a replacement for this we would need a continuity test done, and a diagnostic report to attest that the Heat Link is not functioning properly. We checked the device and it seems to have been out of warranty for over a year now, to be more precise it ended on February 20, 2022, so even with the diagnostic report a replacement would not be possible.

[Maurio]

Ok no problem. I think I will leave it then in that case as it seems I would need to purchase a new thermostat regardless due to it being out of warranty.

please feel free to log this incident in case it is needed for product development. As mentioned, it is not clear if the heat link caused the PCB to fail or the other way around but it may be worth looking into how better to protect the two devices from combined failure should one of them go wrong.

Thank you for your help.

[Paul_R]

You can rest assured that I'll log that in and make sure that it will be passed to the suitable department for further reference. Is there anything else I can assist you with at the moment?

[Maurio]

No that is all for now, thank you!

[Paul_R]

It was my pleasure. I'm going to close this thread now, but if anything else comes up, feel free to reach out. Have a wonderful day ahead!