Motorized valve on return

[Jamesplumber92]

When you have your MV on the return is there any danger of the first rad on that circuit heating up?

 

[SJB060685]

You mean the CH valve on the return and the first rad heating up? If the valve is closed then you won't get any circulation from the pump when HW is calling. You might however get whats called thermal drift, whereas the hotter less dense water travels up and towards the radiator and replacing the cooler and more dense water.

 

[Jamesplumber92]

Ok, is it enough of an issue to make you put your MVs on the flow?

 

[SJB060685]

Thermal drift can happen wherever the valves are. If you put the MV on the flow it should prevent this drift when HW is calling but you could still have the drift from HW return back up through, in which case use an NRV on the CH return.

 

[EvilDrPorkChop]

Won't make a difference if your system is piped correctly.

 

[EvilDrPorkChop]

In which case use an NRV on the CH return.

Tbh that would be bad practice IMO. I'm not convinced any NRVs are properly tested and rated for CH use. Then when something like this fails you'll have no flow round the system.

 

[SJB060685]

Tbh that would be bad practice IMO. I'm not convinced any NRVs are properly tested and rated for CH use. Then when something like this fails you'll have no flow round the system.

I do agree with you yes and technically, like you say if the system is piped correctly you shouldn't get any reverse circulation but reverse circulation and thermal drift are to different things and I have known the latter to occur.