Nest calling for hot water, but schedule and hot water disabled

[Discovery3]

HI there

I have two separate unlinked nest installations - both are doing the same thing.

The schdule is disabled and hot water is off. However both installations will call for hot water from the boilers.  They do this at random times.  I'm not sure how to disable this, but the safety temperature is set very low, and bacteria proteciton is off.  Not sure what else might be causing this problem.  

Any ideas ?

Rgds

Richard.

[Houptee]

Are you in USA?

Safety temp is if you turned off the Nest the heating system would turn back on if the house fell below the safety temp to keep pipes from freezing.

When you say they randomly turn on the boiler that is normal it keeps the house at whatever temperature you set the Nest for. If you have it set for 68 deg F it randomly turns on the heat to keep the house at 68.

Not sure I understand what the problem is.

[Discovery3]

Safety set at 4 Celsius and I'm in the UK. Outside temperature is greater than 9 Celcius outside. Something is calling for hot water (it is not turning the heat on to the radiators). I can't see why it is doing so. If:

- hot water is off

- nothing is scheduled

- ambient temperature is above safety; and

- bacteria setting is disabled

Why is the Nest calling for hot water ?

Rgds

[Houptee]

Sorry I am not familiar with the UK version of the Nest with heatlink etc.

Hopefully someone else can assist you.

[Frustratedddd]

A couple of questions to start off with.

Would this be a new install?

Both sets doing exactly the same thing, fault that is?

Have the old programmers/timers been left in the system?

You have 2 boilers and 2 Nest sets operating each boiler on their own?

[Discovery3]

Yes I have one that has been installed for a year, and this one about noon will fire the boiler. Has done since we installed in. No schedule etc set so no obvious reason for it to fire.  I have a second property and we've just put the nest in replacing a standard timer. Now that second install is doing the same. It had the hot water cylinder up to 40 degrees Celcius yesterday. All old timers have been removed.  Just seems odd.

[Frustratedddd]

OK, that makes more sense now, you have 2 stats is 2 houses.

I assume you have both set to System Boiler as you have a hot water tank? You have an icon in the app showing Thermostat and Hot Water?

Take a look in the App at the following: Open the app - open the water icon - top right click the cog - see if the slider is set to ''On''

Try also looking at this: open the water icon - touch schedule, and see if any orange icons there.

I would suggest a factory reset normally, but having both doing the same in seperate locations just sounds odd.

Using common sense, then for both to work exactly the same way means there could be a wiring issue. Do you have a picture of the Heat Link connections you can upload?

[AlexD]

Hi, thanks for reaching out to us here @Discovery3. I would be happy to try and assist. 

Thanks also for the input @Frustratedddd and @Houptee, always appreciated.

Do you happen to know about the Bacteria prevention feature and if it is enabled? 

You can read all the details about this feature here but in short, this will turn on the hot water if the schedule has been on for at least 2 consecutive hours across 2 days, to reduce the risk of Legionella bacteria growing in the water. The link also shows the steps to turn it off. Just to test, turn it off and see if the activation go away. If it does, then you can enable it back or keep it off, though I would recommend you leave it enabled. 

[Frustratedddd]

I think you will find he mentioned that in the first post.

The schdule is disabled and hot water is off. However both installations will call for hot water from the boilers. They do this at random times. I'm not sure how to disable this, but the safety temperature is set very low, and bacteria proteciton is off. Not sure what else might be causing this problem.

[AlexD]

You are correct @Frustratedddd I do see now that this was also mentioned. Seems to have slipped by me.

In that case it would be best next to proceed with a test on the Heat Link, to see how the internal relays behave @Discovery3.

With the Nest app, go next to the Heat Link, for any of the 2 units. 

1. Select the thermostat heating control and turn down the temperature to make sure the screen is black, heating is off. 

2. Turn the temperature up until the screen goes orange, heating on, and listen for a clicking noise from the Heat Link.  

3. Turn the temperature down until the screen goes black and listen for a clicking noise again,

4. Switch to the hot water control in the app and boost the hot water. Listen again for any clicking noise.

5. Stop the boost and listen for any clicking noise again.

This way we can test how the relays inside of the Heat Link behave. 

[Vladut]

Hello @Discovery, if you can catch them that would be great. Also is worth checking the wiring from the valves to the boiler (if you haven't done that already). Please keep me posted!

[Discovery3]

I've done that already.  The relays click and then do as expected. So for hot water the zone value to the hot water tank opens and the circulation pump comes on then the boiler fires.  For our central heating the zone value to the circulation pipes open and that pump starts and then the boiler fires. When you turn things off by the app or by the nest controller everything shuts down as you'd expect.

I've had nest controllers in previous properties and not seen this behaviour.

Rgds

[AlexD]

Thanks for checking. It is good to hear the relays are behaving as expected.

Did you happen to be at either of the locations when the behavior occurred?

I would be curious to see if first, the display was orange or black when this occurred and if there was any water drop icon on the thermostat display. 

[Frustratedddd]

Did you have a look at the parts I mentioned?

[Discovery3]

The wiring looks fine, and everything seems to be working fine, except that the nest appears to call for heat when not expected.  I'll see if I can catch the boilers on and then we can test the wiring to see what is calling for water.  The more you dig into it the less straight forward it is.  For instance my understanding is that if a zone value sticks open then that could create 240volts on the boiler demand wire.  

[Paul_R]

Hi there! Have you managed to check the last message?

[Discovery3]

Yes - but I am having to catch the boiler on when it should not be - bit trickybut will come back to you when I've got it.

[Paul_R]

Alright then. We're going to wait for your message.

[OannaCG]

Hey there! Just wanted to check if you managed to see our message above. 

[AlexD]

Hey there, I haven't heard from you in a while so I'll be locking this thread. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the community. Thanks, AlexD.