Nest Learning Thermostat 09AC 3rd Gen - gas boiler operates independently

[stevetwood]

My 3rd Gen Learning Thermostat was installed by a local Nest Pro. He changed it from a Thermostat E to a 3rd Gen Learning Thermostat. At the time of the Nest 3rd Gen install, my gas boiler started operating independently of the Nest app and fires up regularly day and night for 2-5 minutes burning gas. I have had the Nest Pro back, he spent an hour checking the install and said the 3rd Gen is installed correctly! I have now replaced the Danfoss 3 way physical motorised valve and pipework and the Honeywell hot water tank thermostat and the boiler continues to fire up and burn gas for several minutes, then switch off, only to ignite again immediately afterwards. 

Today, I switched off the boiler and all the electronics for the hot water system and heating system, disconnected the Gen 3 thermostat from its powered holder and switched them all back on again to reboot them. Now the Gen 3 thermostat refuses to talk to the Heat Link and I get an H71 code on the Gen 3 thermostat and the heat link just shows a permanent yellow light.

I'm at the end of my tether on this and ready to scrap the Gen 3 system and start again with another brand of Smart Thermostat.

Can you help me overcome the H71 link error first and then help me help the Nest Pro installer to diagnose the problem with the boiler just firing up when the app is set to hot water and heating both set to Eco/Off.

The Thermostat E worked brilliantly for a year - I installed it myself with the excellent instructions and it worked first time. I later upgraded to the 3rd Gen Nest because I wanted to remotely control the hot water on my boiler too. Its looking like I made an expensive and massive mistake, and now I can't go back to the Thermostat E easily because I have thrown away the original boiler controller when the 3rd Gen Nest Controller was installed by the Nest Pro.

I have a Potterton Suprima 80L gas boiler

[AlexD]

Thanks for reaching out @stevetwood . I am sorry to hear you are facing difficulties with your thermostat and I would be happy to try and assist. 

Let's see what we can do to have the thermostat connected back and we can check other details after. First a few details for us to log together so I can get a better understanding of the details there: 

1. What is the colour of your Heat Link's light?
2. How is the Heat Link being powered when you're trying to pair it? Over the L/N connection on the Heat Link?
3. When was the thermostat installed?
4. How long after the installation did the issue occur?
5. In what order did the installer set up the device?
   • Was the display paired with the Heat Link when they were close to each other and then moved to the usage location or was it paired with the Heat Link from its usage location?
6. Have you had any recent power cuts in your area? 
7. Was the Nest thermostat moved to a new location? During the troubleshooting you've done so far from the original location?
8. What is the distance between the Heat Link and Nest thermostat? Are the Heat Link and display on the same floor?

[stevetwood]

Hi @AlexD ,

Thanks for the offer to help.

1. I've followed the nest.com/h71 instructions, rebooted the Heat Link for 20 seconds and placed the Thermostat next to the Heat Link and now got the Heat Link connected to the Thermostat, the Heat Link light is now green.

2. It's connected over the LAN to the Thermostat.

3. Autumn 2022

4. Whilst the Nest Pro installer installed the solution, I requested him back a week later and he said he thought the system was working properly but could not understand or explain why the boiler kept firing up and pointed his finger at the motorised 3 way actuator valve which controls the hot water/heating valve. I've now just replaced that 3 way valve for a new factory one, like for like. Nothing in the system has changed.

5. It was paired with the Heat Link in the usage location at the time of installation

6. I switched the gas boiler off in May this year because we don't require central heating and I now heat the hot water tank with a solar diverter which heats the hot water tank via an electrical immersion heater.

7. No - but I moved it closer to the heat link to re-establish the connection between the two Nest devices

8. About 8 metres on the same floor - I will move the Thermostat now so it within 1.5 m of the Heat Link

Both the Water Heating and the Heating are set to OFF on the Nest Thermostat and the App - In fact I have now cleared each and every day in the schedule for both heating and hot water and still the boiler fires up, burns gas for a couple of minutes and then stops burning gas.

[AlexD]

It's great to hear that it's connected back. Thank you for all the information provided. 

Did you happen to notice any pattern to the activation, like a particular time of day? 

Also, did you happen to catch any of these activations to see if the display on the thermostat, or in the Nest app, turned to orange and to a higher set temperature? 

[stevetwood]

Hi @AlexD,

Thanks again for your help.

Did you happen to notice any pattern to the activation, like a particular time of day? 

It will do it all day and night. The boiler turns itself on, burns gas for 1-2 minutes then switched itself off, then 5 minutes later the boiler receives another call for heat, and does a 1-2 burn then switches itself off. 

Also, did you happen to catch any of these activations to see if the display on the thermostat, or in the Nest app, turned to orange and to a higher set temperature? 

Meanwhile the Nest Thermostat 3 was set to heat off and water off with no heat schedules set in the app, the ambient room temp of 22C was showing along with the green leaf. The screen was a black background and the numbers were in white. It is as though the boiler is completely ignoring the Nest device. The Heat Link had a single green light and I didn't call for heat by depressing the button on the heat link.

[AlexD · Accepted solution]

Thank you for all the details. Next, let us have a look at the heating history page. In the Nest app, select the thermostat heating side and at the bottom you'll see the energy history. This will be a record of the past several days and activation it logged.

Tap on each of the past days to get the expanded detailed view for that day. All activation, for heating as it will not log it for water, with orange dots at the time that a activation was logged and inside that dot the temperature for which it was logged. If you see any of these dots that should not be there tap on them. You should get a description on what activated the heating at that point for that temperature. Let me know what you managed to find there, you can also take some screenshots if you want and share them here. 

[stevetwood]

Hi @AlexD ,

Thank you so much for your help, I'm hoping that I have found the solution to my trouble, I'm keeping my fingers crossed. The boiler continued to fire up for 45 seconds overnight several times every hour as it received a 'heat call' from somewhere.

On my 21 year old Potterton Suprima 80L, there is, in plain sight - but that doesn't mean that Captain Observant here has ever seen it before in the previous 22 years, a Temperature Control for the boiler. A plastic knob that you can turn easily turn with your fingers, which is even marked, "Temperature Control".

And I quote from the Potterton Suprima 80L user manual.

"Confirm the Status LED shows continuous Orange (Yes, check). Turn the temperature control knob to adjust the radiator temperature between approx 55C and 82C (there are no values, just an increasingly sized curved line printed on the surface surrounding the Temperature Control knob) Hot water temperature is usually controlled by a thermostat on the hot water cylinder (Yes, check and set by me to 57C)

This "blooming" knob controls the temperature of the water for the central heating system feed! The value on the dial was set at ⅔ max range. I have turned it down by half that value as I don't need central heating in the summer and so the boiler is not trying to heat the central heating feed water adjacent to the boiler anymore...... I can even turn the boiler off at this point without disconnecting the electrical supply, which is something I was doing before.

I want to give it another 24 hours, but I think I have found the culprit. And all the components that I previously replaced probably didn't need changing...

Feeling a bit of a fool, but I am very grateful that you have caused me to think through the problem and arrive at a probable solution and cause. I couldn't work out where the call for heat to the boiler was coming from. The Nest 3rd Gen thermostat was set to off for both central heating and hot water, but the boiler would regularly fire up and burn briefly and then switch off and the light on the boiler would flash green to say that the heating request had been satisfied from the last burn. A few minutes later the light on the boiler would then turn to flashing orange and green and then the boiler would fire up again. The hot water in the cylinder for use in showers and taps is heated by a solar diverter with 'free' electricity from my solar panels to 58C via the hot water tank immersion heater - so there shouldn't have been heat calls from the hot water when hot water wasn't being extracted from the tank.

I will turn up the boiler temperature in the autumn and winter as this control knob affects the temperature of the water fed to the radiators.

Thanks again for your logical approach and process to help me. 

Best Regards

Steve

[Paul_R]

Hi there @stevetwood! I'm glad that the conversation with my colleague has helped you determine the possible culprit. How are things going? Was that the issue in the end, would there be anything else we can do for you?

[stevetwood]

@Paul_R @AlexD 

Thanks everyone, you can close/lock this query for others to benefit from.

I think the issue is with my boiler, even though I have turned off the boiler at the temperature control on the boiler, it sits there flashing orange and green which translates to a request for heat for the boiler to satisfy. I suspect there is a thermometer within the boiler which is overreacting because the local water temperature is lower than the 55C-82C temperature control on the the boiler temperature control.  The ambient temperature is currently 18-22C way above the permanently set 9C ECO setting on the 3rd Gen Thermostat and the hot water is switched off at the 3rd Gen Thermostat with no heating schedule currently set - I'm using a solar panel diverter to heat the water through my hot water tank immersion heater. I'll get the boiler service people out again to check whether the boiler is too sensitive for a call for heat from the localised water temperature.

Thanks again

[Paul_R]

It's always our pleasure to help. We'll go ahead and lock this thread, but if anything else comes up, please feel free to reach out again. Have a wonderful day ahead!