I have a Grundfos Alpha 3 pump in an underfloor heating manifold and Nest thermostat all connected up in a wiring centre. From what I understand the pump is wired with just a live and neutral.

 

Is the pump supposed to turn off when there is no demand from the thermostat? I still hear it turning and see that its using around 4 watts of power. How is the pump supposed to know when to turn off?

Edited July 27, 20233 yr by Rehan Saeed

The thermostat calls for heat, this should send a signal for the boiler to start and also tell the pump to start. When there is no call for heat the boiler and pump should be switched off.

 

Within the wiring centre there should be dedicated connection for the pump. If remember correctly pump has a slight delay in starting after a call for heat.

1 minute ago, JohnMo said:

The thermostat calls for heat, this should send a signal for the boiler to start and also tell the pump to start. When there is no call for heat the boiler and pump should be switched off.

 

Within the wiring centre there should be dedicated connection for the pump. If remember correctly pump has a slight delay in starting after a call for heat.

So the power to the pump is cut when this happens? This decision must be made from the Nest Heatlink and then sent to the pump and boiler demanding heat. Is there a reliable wiring diagram I can look at for this?

 

I don't think that is happening right now and my plumber didn't seem sure the wiring was correct.

29 minutes ago, Rehan Saeed said:

I have a Grundfos Alpha 3 pump in an underfloor heating manifold and Nest thermostat all connected up in a wiring centre. From what I understand the pump is wired with just a live and neutral.

Can you post a picture and more details of this "wiring centre"

 

Without knowing what is controlling the pump, nobody can say id it operating how the system was designed or not.

 

If designed properly, of course the pump will not run when there is no demand.

This bloke at the 8 minute mark mentions that in some systems the pump is always powered and turns on when it notices a flow of water from the zone valve opening while in other systems the pump is turned off when there is no demand.

 

In my case, the Alpha 3 pump has some features such as turning the pump on briefly in summer to stop it seizing, so I'm guessing that this pump requires power all the time?

 

 

Ah this is a "clever" pump, controlled by an APP.

 

Sorry I will bow out here, it is far too complicated and wants to make up it's own mind when and how to run. Not what I would want in my system.