Hot water circulating pump does not stay on

[Gavdaddy]

Circulating pump on hot water system turns off when water in tank is at temperature. We have a four story house and a Worcester system boiler and we want the pump to stay on circulating during hot water demand periods. Nest display 3.4 and Heat Link Amber-2.5. Is it a setting or wiring problem ? I saw @DragosC response to the opposite issue of the pump staying on.

[Jenelyn_O]

Hi Gavdaddy,

Thanks for reaching out. I'm sorry for the delay. A few questions: do you see any messages or codes in your Nest Learning Thermostat or in the Nest app? In what states are you located? 

Best,

Jenelyn

[Gavdaddy]

No messages or codes 

Located in Europe

[Gavdaddy]

My guess is that it is a wiring issue in the Heat Link

[AlexD]

Thank you for all the information @Gavdaddy . Just to clarify, you have a hot water tank and even though you have the hot water scheduled to be on, when the temperature set on the hot water tank is reached, it turns off, correct? 

[Gavdaddy]

Yes the circulating pump turns off. We have a system boiler on the ground floor and hot water tank and circulating pump on the 3rd floor. We want the water to circulate during the set period and heated as necessary.

[UanaC]

Hello there! Thanks for the information! When the hot water tank temperature is reached, it will turn off. This is how the hot water tank is designed to work. You can set the hot water to be on all day, in the Nest App, but the thermostat on the tank will turn it off when the temperature is reached. 

Many thanks, Oana.

[Gavdaddy]

Oana,

Thanks, I’m aware of how the thermostat and tank work which is fine. What I need is that the circulating pump, which is also connected to the same heat link as the tank, continues to run during the hot water on period irrespective of the tank temperature/thermostat.

[OannaCG]

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

[Gavdaddy]

I did and the message above is my response

[OannaCG]

This installation guide should be useful: https://goo.gle/2pTMYLC . Should you have any questions, feel free to ask me.

[Gavdaddy]

Installation guide is not useful as it does not address how to configure to control a house with a system boiler and hot water circulating pump. It seems N’est is intended only for small bungalows with combi boilers. What is your solution?

[Paul_R]

Hello @Gavdaddy! I checked the previous messages and I'm sorry that you've encountered this issue. From what you've told my colleagues, it seems that you have connected the circulation pump and the hot water tank to the same Heat Link. Connecting the circulating pump to the Heat Link is untested and we do not advise it, as there are no specifically designated terminals for it, and in consequence you might encounter situation like this, where it doesn't function as you would expect it. There are no steps available to troubleshoot on something like this, and I'd recommend you to get a professional heating engineer to take a look at your set-up. Please let me know if there is anything else besides this, that I can help you with.  

[Gavdaddy]

This was installed by a heating engineer. How would you recommend that the heating pump is controlled by Nest?

[OannaCG]

The Nest Thermostat (3rd generation) is also compatible with the system boiler, as you can see in the installation guide. As my colleague mentioned above, the Heat Link doesn't have any specifically designated terminals for the circulating pump, so we can't provide you with any troubleshooting steps for this situation. The Heat Link will send the signal for hot water heating as long as it's scheduled. If another part of the system, like a thermostat on your hot water tank turns it off, it's out of the Nest thermostat's control.

[Gavdaddy]

So basically a system boiler with a circulating pump cannot be controlled correctly by Nest. If that is the case Nest is obviously for small houses and apartments.

[AlexD]

The Nest thermostat can control a system boiler. It acts like an on/off switch for the hot water based on the schedule set. However, the hot water tank is governed by the thermostat mounted on it. It has to turn off the tank for safety reasons, else it would keep heating the water causing possible damage to the system. The thermostat sends the signal for the hot water heating to be on as long as it is scheduled, that is what is designed to do. Other parts of the system may have dependencies in their functionality with other components, not the thermostat. For example, the temperature of the water in the radiators from the boiler is set on the boiler itself and will determine how fast a room heats up, the thermostat just determines how long that heat has to be on to achieve the desired temperature. I would recommend you talk to your installer to see what the best course of action would be for that particular pump you wish to control. 

[Gavdaddy]

The zoned heating system works fine and heating water temperature is as required.

problem is that the heat link turns off the circulating pump when the tank is at temperature rather than continuing circulation for the period hot water is desired. Are you confirming that Nest is not suitable for larger houses with circulating pumps. The installer will ask Nest the same question. I wanted to get it clear that Nest is only interested in solutions for small properties before we go out to the wider community.

[AlexD]

The Heat Link does not stop the request as long as it is scheduled to be on. It is the thermostat on the hot water tank that stops the request. You can schedule the hot water to be on 24/7 but the hot water tank will still decide when to turn off based on its internal thermostat, that is not something the Heat Link controls. 

[LarisaL]

Hi there, just checking in! Did you see the message from my colleague? 

Thanks, Larisa

[Gavdaddy]

Certainly did. It is of no help and basically states that Nest is not a suitable solution for ansmedium to large house with a hot water circulating pump. Do you have a recommendation for a vendor/equipment that can used to address the Nest short comings or is it a case of dumping Nest and replacing all 4 units with a more capable system?

[Vladut]

In this situation my best recommendation would be to check with a local installer for another opinion. I can recommend you some of our Nest Certified installers for one. You can find one here: https://goo.gle/37Nwshb. Let me know how it goes!

[LarisaL]

Hi there, just checking in! Did you see the message from my colleague?

[Gavdaddy]

Yes, did you have something to add. Solution appears to be that Nest can't help for anything besides simple properties.

[AlexD]

While the thermostat is compatible with most systems it is certainly not compatible or convenient for all situations. I will go ahead and close this thread. If you have any other questions or anything else that comes up, make sure to open up a new thread.